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Influence of Moisture Degradation on Fibre-Epoxy
Interface in Pre-Preg Laminates
i
ABSTRACT
The effect of moisture absorption on the mechanical behaviour and on the fibre/matrix
interface of HTA/ 6376 composite material was investigated. In order to determine the
effect of stacking sequence on the moisture absorption, two different laminate
configurations, [08]s and [06 902]s, were considered. The specimens were immersed in de-
ionized water at room temperature (19°C ± 2). The absorption characteristics of carbon
fibre epoxy laminates were investigated by the measurement and analysis of the
weight change and hygrothermal induced expansion. The specimens exhibited Fickian
Diffusion behaviour and absorbed on average 0.8% moisture by weight over the complete
exposure period. It was found that the specimen lay-up sequence affected the overall
moisture absorbed, with a higher moisture content in the [06 902]s specimens. The
interlaminar shear strength (ILSS) of both dry and wet specimens was determined using a
double-notched test method (ASTM D3846-08). A statistical analysis of the results
determined that the absorbed moisture caused an increase in ILSS values by up to 18.7%.
The increase in ILSS is dependent on the exposure time, with the four month immersed
specimens having increased by a substantial amount.The results obtained have been found
to be in line with data reported in literature. The predominant reason for the increase in
ILSS is due to the increase in the flexibility of the resin due to an increase in moisture
content. Digital Image Correlation (DIC) was used in order to determine the strain and
displacement in the x- and y-directions. Fractography analyses were conducted to detect the
type of accumulated damage and to investigate the effect of moisture on the fibre/matrix
interface. This was investigated by Scanning Electron Microscopy (SEM).
Keywords: Moisture absorption, Hygrothermal, Moisture Diffusion, Diffusivity,
Interlaminar Shear Strength
ii
DEDICATION
To my dad, who taught me to climb as high as I can dream and that the best kind of
knowledge to have is that which is learned for its own sake.
iii
ACKNOWLEDGEMENTS
From the formative stages of this thesis, to the final draft, I owe an immense debt of
gratitude to my supervisor, Dr. Trevor Young, who has been the ideal supervisor. His sage
advice, insightful criticisms, and patient encouragement aided the writing of this thesis in
innumerable ways.
I would also like to thank Dr. Kali-Babu Katnam whose steadfast support and tireless help
for this thesis was greatly needed and deeply appreciated.
For their efforts and assistance, a special thanks as well to Mr. Adrian McEvoy and Mr.
Robert Telford.
Finally, I would be remiss without mentioning Dr. Walter Stanley, whose important
contribution of talent and time given unselfishly in proceeding with this work.
To each of the above, I extend my deepest appreciation.
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TABLE OF CONTENTS
ABSTRACT ........................................................................................................................ i
DEDICATION .................................................................................................................. ii
ACKNOWLEDGEMENTS ............................................................................................. iii
LIST OF FIGURES .......................................................................................................... vi
LIST OF TABLES ......................................................................................................... viii
NOMENCLATURE .......................................................................................................... ix
1 INTRODUCTION ...................................................................................................... 1
1.1 Background ......................................................................................................... 1
1.2 Outline of Thesis ................................................................................................. 3
1.3 Objectives ............................................................................................................ 3
2 LITERATURE REVIEW ........................................................................................... 4
2.1 Introduction ......................................................................................................... 4
2.2 Variables affecting Moisture Absorption ............................................................ 4
2.3 Effect of Water Temperature and Relative Humidity Variations ........................ 5
2.4 Effects on Mechanical Properties ........................................................................ 6
2.5 Mass-Gain Ratio and Alternative Measuring Techniques ................................ 12
2.6 Effect of Seawater in Preference to Conventional Methods ............................. 13
2.7 Mechanical Adhesion ........................................................................................ 14
2.8 Natural Fibres .................................................................................................... 15
2.9 Thermoplastic versus Thermoset polymers ....................................................... 16
2.10 Digital Image Correlation (DIC).................................................................... 16
2.11 Fractography studies ...................................................................................... 17
3 THEORETICAL ANALYSIS .................................................................................. 19
3.1 Diffusion and Fick‘s second law ....................................................................... 19
3.2 Interlaminar Shear Strength (ILSS) ................................................................... 22
3.2.1 Equation for calculating the ILSS .................................................................. 22
4 EXPERIMENTAL .................................................................................................... 23
4.1 Material ............................................................................................................. 23
4.1.1 Test specimens ............................................................................................... 23
4.1.2 Conditioning and Specimen Exposure ........................................................... 23
4.1.3 Measurements ................................................................................................ 24
v
4.2 Interlaminar Shear Strength (ILSS) Test ........................................................... 25
4.2.1 Experimental Apparatus and Procedure ........................................................ 26
4.3 Digital Image Correlation (DIC) ....................................................................... 27
4.4 Fractography Studies ......................................................................................... 30
5 RESULTS AND DISCUSSION ............................................................................... 31
5.1 Fickian Diffusion and Specimen Weight Gain .................................................. 31
5.2 Volumetric Expansion ....................................................................................... 35
5.3 Interlaminar Shear Strength (ILSS) ................................................................... 36
5.3.1 ILSS Results .................................................................................................. 36
5.3.2 Stress State ..................................................................................................... 38
5.3.3 Flexibility of Resin ........................................................................................ 39
5.3.4 Limitations and constraints during ILSS testing............................................ 43
5.4 Digital Image Correlation (DIC) ....................................................................... 46
5.5 Fractography Analysis ....................................................................................... 51
6. CONCLUSIONS AND FUTURE RESEARCH .......................................................... 61
6. 1 Conclusions ............................................................................................................... 61
6.2 Recommendations for Future Research ..................................................................... 63
6.2.1 Raman Spectroscopy ........................................................................................... 63
6.2.2 Thermoplastics versus Thermosets ..................................................................... 63
6.2.3 Relative Humidity Chamber ............................................................................... 63
6.2.4 Reversible/Irreversible Effects ............................................................................ 64
6.2.5 Epoxy Resin Toughness ...................................................................................... 64
REFERENCES ................................................................................................................. 65
Appendix A: Turnitin originality report……………………………………………….A1
Appendix B: Specimen Dimensions…..……………………………………………….B1
Appendix C: Drawing of clamp adapted from ASTM Standard D3846-08......….…....C1
Appendix D: Specimen Weight Gain Values....……………………………………….D1
Appendix E: Experimental data from ILSS Test…...……………………………….…E1
Appendix F: SEM Micrographs………………………………………………………..F1
vi
LIST OF FIGURES
Figure 3-1. Fickian Diffusion Curve (Shen and Springer, 1975; Greene, 2007) ............. 21
Figure 3-2. Specimen dimensions .................................................................................... 22
Figure 4-1. Explorer Analytical Balance ......................................................................... 24
Figure 4-2. Shadowgraph Projector ................................................................................. 25
Figure 4-3. Clamp used in ILSS Testing .......................................................................... 26
Figure 4-4. Tinius Olsen H25KS Model .......................................................................... 27
Figure 4-5. Speckled Specimen........................................................................................ 28
Figure 4-6. Strain Master experimental setup (adapted from La Vision, 2010) .............. 29
Figure 4-7. JEOL JCM 5700 (www.jeolusa.com) ........................................................... 30
Figure 5-1. Moisture content (w/w %) - [08]s configuration ........................................... 32
Figure 5-2. Moisture content (w/w %) - [06 902]s configuration .................................... 32
Figure 5-3. Force against Extension [08]s ........................................................................ 40
Figure 5-4. Force against Extension [06 902]s .................................................................. 40
Figure 5-5. Stress against Strain [08]s specimens ............................................................. 42
Figure 5-6. Stress against Strain [06 902]s specimens ....................................................... 42
Figure 5-7. Wet I [06 902]s x-displacement (a) At failure (b) After failure ...................... 46
Figure 5-8. Dry [08]s specimen y-displacement (a). Before failure (b) At failure ............ 47
Figure 5-9. Dry [06 902]s specimen y-displacement (a). Before failure (b) At failure ..... 47
Figure 5-10. Dry [08]s specimen - Strain Exx – (a) At start of load (b) At failure ........... 48
Figure 5-11. [06 902]s Specimen - Strain in the x-direction (a) Dry specimen (b) Wet
specimen ........................................................................................................................... 49
Figure 5-12. Fracture surface of a dry [08]s specimen - magnification x10 .................... 52
Figure 5-13. Fracture surface of a dry [08]s specimen - magnification x1000 ................ 53
Figure 5-14. Fracture surface of a wet [08]s specimen – 2month withdrawal - magnification
x10 .................................................................................................................................... 53
Figure 5-15. Fracture surface of a wet [08]s specimen – 2month withdrawal – magnification
x1000 ................................................................................................................................ 54
Figure 5-16. Fracture surface of a wet [08]s specimen – 4 month withdrawal - magnification
x10 .................................................................................................................................... 55
Figure 5-18. Fracture surface of a dry [06 902]s specimen - magnification x10 .............. 56
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Figure 5-17. Fracture surface of a wet [08]s specimen – 4 month withdrawal - magnification
x1000 ................................................................................................................................ 56
Figure 5-19. Fracture surface of a dry [06 902]s specimen - magnification x1000 .......... 57
Figure 5-20. Fracture surface of a wet [06 902]s specimen – 2month withdrawal -
magnification x10............................................................................................................. 58
Figure 5-21. Fracture surface of a [06 902] specimen - 2month withdrawal - magnification
x1000 ................................................................................................................................ 58
Figure 5-22. Fracture surface of a wet [06 902] specimen – 4 month withdrawal -
magnification x10............................................................................................................. 59
Figure 5-23. Fracture surface of a wet [06 902]s specimen - 4month withdrawal -
magnification x1000......................................................................................................... 60
viii
LIST OF TABLES
Table 2-1. Aspects of property deterioration in polymer-based composite materials (Hull,
1981). ............................................................................................................................... 10
Table 5-1. Moisture content (w/w %) .............................................................................. 34
Table 5-2. Volume Change (%) ....................................................................................... 35
Table 5-3. ILSS values ..................................................................................................... 37
Table 5-4. ILSS percentage increase values .................................................................... 37
Table 5-5. [08]s Specimen - Load and extension values ................................................... 41
Table 5-6. [06 902]s Specimen - Load and extension values ............................................ 41
ix
NOMENCLATURE
Symbol Description Units
D Diffusion Coefficient mm2/s
Dz Diffusion Coefficient in mm2/s
the z-direction
E Elastic Modulus N/m2
F Interlaminar Shear Strength MPa
GIIC Mode II Fracture Toughness MPa
M0 Initial moisture content %
M∞ Maximum moisture content %
P Load at failure N
Tg Glass Transition Temperature K
Vf Volume Fraction %
Vx Displacement in the x-direction mm
Vy Displacement in the y-direction mm
Mass of dry specimen g
Mass of wet specimen g
c0 Initial moisture absorption state -
c∞ Fully saturated moisture absorption -
state
w Width of specimen mm
l Distance between notches mm
Strain -
Strain in the x-direction -
Strain in the y-direction -
Stress N/m2
Stress in the z-direction N/m2
x
Abbreviations
ANOVA Analysis of Variance
CCD Charge Coupled Device
CFRP Carbon-Fibre Reinforced Plastic
DIC Digital Image Correlation
GFRP Glass-Fibre Reinforced Plastic
RH Relative Humidity
RPL Repeated Progressive Loading
SEM Scanning Electron Microscopy
UV Ultraviolet
Chapter 1
Introduction
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1 INTRODUCTION
1.1 Background
In the last two decades, advanced polymer-matrix composite materials have been widely
used as a substitute for traditional structural materials. As high specific strength and
stiffness ratios are required for aeronautical structural components, advanced polymer-
matrix composite materials provide several opportunities for lower structural weight than
conventional metallic components. Initially, composites were only used in secondary
structures, like the interior details and floor, and in less critical-load bearing components
with such examples as hatch doors of landing gear. At present they are being introduced
into primary structures of aircraft such as the wing, fuselage and control surfaces.
Composites also find an increasing use in non-aerospace structures. Marine applications
provide a sizeable growth potential, from sailboats to kayaks. Automobile and construction
applications are also profiting from their low specific mass and very high static strength.
Composites generally have long fatigue lives and are easily maintained and repaired.
However, cost and confidence remain obstacles towards the increased use of composite
materials in all industries. In this regard, for reliable structural design, a detailed
understanding is required related to: fastening methods, damage tolerance, hygrothermal
effects, lightning-strike protection and material compatibility. This thesis investigates the
influence of hygrothermal effects on shear strength of polymer-matrix composites.
The comprehensive understanding of hygrothermal effects is important in order to predict
service-life, maintainability and durability. It will also allow future designers to tailor for
specific applications by selecting the suitable physical and mechanical properties needed
and by choosing from a variety of fibres and resin available. In-service composites are
exposed to harsh environments for long periods of time and thus have a tendency to suffer
from hygrothermal effects. These are mainly due to environmental attacks such as
temperature, humidity, radiation and chemical exposure. In addition, the effect of moisture
should also be taken into account. Moisture is absorbed from the humidity in the
atmosphere. This causes degradation in the material properties and is therefore of much
concern especially in aeronautical applications. Consequently, moisture absorption in
composites has received a growing interest and a great deal of evidence has been collected
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to demonstrate that both physical and mechanical properties can be strongly affected;
thereby affecting the overall performance of the composite. These effects can be examined
from a microscopic point of view, on the scale of fibre diameter, or from the macroscopic
point of view; where the fibre/matrix interface is examined and the overall effects on the
lamina considered. A macroscopic point of view is approached here and the material is
assumed to be homogenous.
Moisture induced degradation in mechanical properties can be due to a number of reasons.
Fibres are insensitive to environmental changes; the susceptibility of the laminates is
mainly due to the matrix. Moisture diffuses through the matrix and fibre/matrix interface.
The absorbed moisture causes physical and/or chemical changes in the matrix, loss of
adhesion of fibre/resin interface, and/or loss of fibre strength and stiffness. The absorbed
water also softens the matrix resin and thus reduces the overall stiffness of the laminate. A
considerable reduction of tensile strength, fracture toughness and lowering of the glass
transition temperature (Tg) with increased moisture concentration has been reported (Selzer
and Friedrich, 1997; Choi et al., 2001; Akbar and Zhang, 2008). Compression strength also
decreases and this leads to a larger damage area.
To investigate the influence of moisture ingress on shear strength of polymer-matrix
composites, an existing test method (double-notched test method) was employed in the
current thesis work to characterize the inter-laminar shear properties of both dry and wet
composite specimens. Testing was conducted after two time periods - two and four months.
The manner in which composite materials absorb moisture is dependent on a number of
factors some of which include: temperature, fibre orientation, density, diffusivity and fibre
volume fraction etc. While not exhausted, several of these factors have been investigated
(Whitcomb and Tang, 2001; Bao and Yee, 2002; Vaddadi et al., 2003; Baker et al., 2004).
Two lay-up configurations were examined in order to determine the effects of different
stacking sequence on the diffusion parameters. The specimens were exposed to a 100% RH
environment, by fully immersing them in water. To utilize the full potential of the
carbon/epoxy laminates, their fracture mechanical behaviour under these conditions also
had to be determined. All specimens tested were examined visually and with the aid of
optical microscopes. In order to thoroughly detect the type of accumulated damage,
3
fractography studies were conducted. The effects of moisture on the fracture surfaces of the
specimens were examined using Scanning Electron Microscopy (SEM).
1.2 Outline of Thesis
The thesis follows a course, from a review of existing work, through to the presentation of
the results of the investigation. The purpose of this section is to provide a brief overview of
the chapters. Chapter 2 describes the concept of moisture diffusion, its variables and its
implication on in-service applications. It is written with the presumption that the reader has
a solid grasp of composites but is not familiar with the physical affects due to moisture
absorption. Chapter 3 investigates Fickian‘s Law of diffusion and the application in relation
to composite materials. Chapter 4 discusses the experimental work undertaken, its methods
and procedures. Implications of the assumptions made in Chapter 3 are discussed in
Chapter 5 where the results of Chapter 4 are also presented. In Chapter 6, overall
conclusions are drawn, limitations are discussed, and further research is proposed.
Appendix A-F contains the data compiled during the experiments, detailed drawings of
specimens, parts manufactured to aid in the testing procedures and SEM micrographs.
1.3 Objectives
The objectives of this project were:
1. To predict and analyse the maximum weight gain of carbon/fibre laminates as a
function of exposure time.
2. To determine the diffusion coefficient of the laminates.
3. To investigate the effect of moisture absorption on the fibre/matrix interface and
evaluate the overall effects on the laminate by performing interlaminar shear
strength tests.
4. To utilise Digital Image Correlation (DIC) to determine the stress and strain fields
on composite material subjected to hygrothermal effects.
5. To examine the difference of the fracture profiles of dry and wet specimens by
using Scanning Electron Microscopy (SEM).
Chapter 2
Literature Review
4
2 LITERATURE REVIEW
2.1 Introduction
The study of composite materials involves many topics, of which include manufacturing
processes, strength of anisotropic materials and micromechanics. Consequently, no single
individual can claim a complete understanding of all these areas. Therefore, in order to
establish a complete and comprehensive understanding of moisture absorption in composite
materials, it is necessary to evaluate and address critical points of the current knowledge of
researchers in this area. This also provides the gaps and limitations towards a more specific
topical area.
This literature review has three main themes, (1) the variables affecting moisture absorption
including; immersion temperature and the effect of seawater. More importantly, (2) its
effects on mechanical properties of composite materials, including, polymeric composites
most susceptible to moisture absorption. In order to fully establish the effect on the
specimens, (3) the use of Digital Image Correlation (DIC) and Scanning Electron
Microscopy (SEM) was investigated and the limitations of these methods established.
2.2 Variables affecting Moisture Absorption
Perreux and Suri (1997) highlighted that the degradation of the material is mainly
influenced by two things: mechanical and environmental stresses. These factors are
interrelated; if damage has occurred in the structure, this leads to an increase in the
moisture absorbed by the composite material. Equally, if the material has undergone
hygrothermal ageing it would be more easily susceptible to damage.
Akbar and Zhang (2008) reported that there exist critical factors which influences the way
in which composite materials absorb moisture. These factors include; temperature,
reinforcement orientation, fibre volume fraction, and the density, polarity and permeability
in regard to the fibre nature. The surface protection, diffusivity and area of the exposed
surface are also key points. Choi et al. (2001) investigated the effect of void content on the
hygrothermal behaviour of composite laminates. By observing the diffusion rate coefficient
and water absorption behaviour of unidirectional laminates containing different amounts of
5
void fraction, it was evident that laminates containing a higher number of voids, follows
non-Fickian diffusion characteristics at the initial stages of water absorption.
Bao and Yee (2002) highlighted that in theory, diffusion can be predicted solely from the
fibre volume fraction and the neat resin of a composite but that in reality the situation is
much more complicated. In advanced composites a large amount of interface is present, as
the fibre diameter and inter-fibre distance are both extremely small. Bao and Yee explained
the influence of inadequate wetting of the fibre/matrix interface; this is reviewed in Section
2.7. Similarly, Whitcomb and Tang (2001) studied how the effective diffusion varies with
fibre volume fraction (Vf). The effective diffusion for low to moderate fibre fractions (Vf <
40%) are essentially the same, following Fickian‘s Law, however a big difference exists for
higher fibre fractions (Vf >40%).
The effect of fibre orientation and variation in thickness of the specimens on the absorption
of water has been investigated by a number of experimentalists (Selzer and Friedrich, 1997;
Choi et al., 2001; Akbar and Zhang, 2008), all obtaining similar results. The diffusion rate
and the equilibrium water uptake are not influenced by the stacking sequence because the
penetration length of water molecules and the resin content are not changed. Judd and
Wright (1978) determined that irrespective of fibre and fibre surface treatment, or resin
type, the interlaminar shear strength of composite material decreases by about 7% for each
1% of voids up to a total void content of about 4%. It is important to characterize the void
content of composite materials as numerous properties are affected by this.
2.3 Effect of Water Temperature and Relative Humidity Variations
According to Akbar and Zhang (2008), the amount of moisture absorbed is found to be
independent of the exposure temperature, but directly proportional to the relative humidity
of the environment. Similar to the findings of Asp (1998), Selzer and Friedrich (1997)
experimentally examined the effect of moisture absorption on the fracture toughness of
carbon fibre-reinforced polymers by immersing specimens into three baths of different
temperatures: 23, 70 and 100°C. They found that the decrease in fracture toughness when
tested in mode I and mode II were independent of the temperature of the baths, but solely
related to the moisture content. Selzer and Friedrich (1997) noted a decrease of 8% in the
6
half saturated specimens in mode I and a decrease in the fully saturated specimens of
around 15% in the mode II fracture toughness ( values, when compared to the dry
specimens. However, the results are not consistent with the work obtained by Russel and
Street (1985) who observed a greater decrease in fracture toughness with an increase in
temperature. They found that the values obtained were significantly different at 100°C than
at lower temperatures, with the effect of moisture causing a decrease of up to 22% in the
fracture toughness at a 100°C. Later in the research work of Selzer and Friedrich (1998),
they confirmed their results obtained previously (1997) and also verified that an increase in
the water temperature only results in an increase in the absorbed moisture, leading to a
reduced time in saturation of the specimens. Similarly, Baker et al. (2004) anticipated an
increase in temperature of 10°C would cause the diffusion rate to double. The diffusion of
moisture into a composite matrix over time varies exponentially with temperature. Vaddadi
et al. (2003) varied the relative humidity from 50% to 85% in their chamber but kept it at a
constant temperature of 85°C. When plotting the relative weight gain (%) against time, they
noted that both curves were nearly equal at the diffusivity of the initial stage of exposure.
Choi et al. (2001) noted that the diffusion coefficient of a specimen immersed in a water
bath (100% RH) at 70°C is bigger than the one in a 95% RH chamber held at the same
temperature. They found that the equilibrium water uptake obtained in the humidity
chamber had a larger amount of saturated water uptake than that in the bath. These
conclusions are not consistent with the work completed by Hao et al. (1992), who observed
higher moisture content for carbon/PPS laminates when exposed to higher relative humidity
environments. For specimens exposed to a fixed relative humidity environment at high
temperatures, the moisture content is low. It can thus be concluded that a laminate exposed
to a low temperature/high relative humidity environment will have higher moisture content,
than when exposed to a high temperature/low relative humidity environment.
2.4 Effects on Mechanical Properties
Akbar and Zhang (2008) experimentally investigated the presence of moisture in a polymer
composite. Polymers undergo both dimensional and property changes when exposed to a
hygrothermal environment. When examining composites which utilize polymers as
matrices, the sensitivity to environmental changes was found to come from the matrix;
7
since fibres are insensitive to these changes. As a result, if a quasi-isotropic composite is
exposed to such an environment it affects the transverse, shear and longitudinal properties.
According to Choi et al. (2001) longitudinal properties dominated by fibre properties in
unidirectional composites may not drop so noticeably but such properties as compression
strength and interlaminar shear strength are significantly affected by the moisture absorbed,
especially at high temperatures. This is due to the fact that the influence of moisture and
temperature affects the matrix and interfacial performance. Longitudinal tensile strength is
a fibre dominated property and thus moisture and temperature will not cause adverse
effects. However, the longitudinal compressive strength and interlaminar shear strength are
dominated by the matrix of the composite and is therefore greatly affected.
At room temperature the reduction of interlaminar shear strength may not be significant but
when operating at temperatures between 100°C and 130°C these reductions can be up to
50-60%. Akbar and Zhang (2008) found a 13% decrease in the interlaminar shear strength
(ILSS) for carbon/epoxy laminates subjected 60°C/100% RH (immersion). They found that
the water absorbed by the epoxy laminates, causes reversible plasticization of the matrix
and combined with temperature effects, these factors cause significant changes in the
matrix toughness thereby affecting the laminate strength. When exposed to different
immersion time periods, the ILSS is seen to weaken over time. The epoxy matrix absorbs a
significant amount of moisture, where the fibres absorb little or no moisture. This leads to a
significant mismatch in moisture-induced volumetric expansion between matrix and fibres,
causing the evolution of localized stress and strain fields in the composite at the interfacial
region (Akbar and Zhang, 2008). According to Hull (1981) these stress and strain fields
have different gradients in the material; due to non-uniform water content and
concentration under non-equilibrium conditions. The build-up of internal stresses can also
occur even when the moisture content in the material is uniform due to different swelling
characteristics of adjacent laminae in a laminate.
Matthews and Rawling (1994) tested multidirectional laminates and observed the effects on
the dominant 0° load bearing layers. When tested in tension, temperature and moisture have
little effect on the failure of the dominant 0° load bearing layers. When tested in a resin
8
dominated situation, such as applied tension or where the resin is required to support the
fibres against buckling in compression, the effects due to temperature and moisture are
significant. For example, a ± 45° CFRP laminate, tested in tension at 130°C and 1.5%
moisture, shows a 40% drop in strength at room temperature. Selzer and Friedrich (1997)
observed the same effect; however they also found that the more the specimens absorbed
moisture, the bigger the reduction. The reduction in strength was up to 66% and they
concluded that the moisture effects were more predominant in tensile tests that were
dependent upon the strength of the matrix and interface.
It was found by Akay et al. (1997) that moisture has no influence on the elastic modulus
but causes a severe decrease on the flexural strength of Kevlar/epoxy resin laminates. This
was also confirmed by Perreux and Suri (1997). This is contrary to the predictions of Hull
(1981), who explained that moisture affects the flexibility of the epoxy resin, thus reducing
the elastic modulus. Changes in elastic modulus have no effect on longitudinal tensile
strength but the longitudinal compressive strength and the interlaminar shear strength are
greatly affected. Baker et al. (2004) predicted for a carbon/epoxy composite, cured at
180°C, moisture absorption causes a reduction of up to 10% in compressive strength for
subsonic aircraft and up to 25% for supersonic aircraft. These figures were surpassed by
Selzer and Friedrich (1997) who found that the compressive strength reduced by up to 35%
for carbon/epoxy 0° laminates and up to 37% for 90° laminates.
Matthews and Rawling (1994) reported that the absorbed moisture causes the resin to
soften, and therefore composites whose properties are resin dominated, will experience
severe reductions at elevated temperatures. This is particularly evident as the glass
transition temperature of the resin is approached. Other effects include; micro-cracking of
the resin or fibre-matrix interface, blistering or delamination.
Thermosetting resins cover a broad class of chemicals and a corresponding range of
physical and mechanical properties can be obtained. The curing agent plays a role in
determining the kinetics of water uptake and the degradation in mechanical properties.
However, in order to effectively explain the reduction in the glass transition temperature
(Tg), an epoxy matrix is considered. The water molecules attach by hydrogen bonding, the
9
water then acts as a plasticizer, thus reducing the Tg. However, when the environmental
conditions change and the moisture diffuses out, these effects are reversible, and some
properties such as the elastic modulus will return to its original value. Moisture absorption
also leads to irreversible effects on material properties, as listed in Table 2.1.
10
Table 2-1. Aspects of property deterioration in polymer-based composite materials (Hull, 1981)
Reversible changes Irreversible changes
Resin Water swelling (1) Chemical break-down by
hydrolysis
Temperature flexibilising (2) Chemical break-down by UV
radiation
Physical ordering of local (3) Chemical break-down by molecular
regions thermal activation
(4) Chemical break-down by stress
induced effects associated with
swelling and applied stress
(5) Physical ordering of local
molecular regions
(6) Chemical composition changes by
leaching
(7) Precipitation and swelling
phenomena to produce voiding and
cracks
(8) Non-uniform de-swelling to
produce surface cracks and crazes
(9) Chemical effect of thermoplastic
polymer content on long term stability
Interface Flexibilising interface (1) Chemical break-down as above
1,2,3,4
(2) Debonding due to internally
generated stresses associated with
shrinkage and swelling and the applied
stress
(3) Leaching of interface
Fibre - (1) Loss of strength due to corrosion
(2) Leaching of fibre
(3) Chemical break-down by UV
radiation
11
De Sá (2007) conducted a study on the ‗Influence of Moisture Absorption on QuasiStatic
and Long-Term Failure of a GFRP Pipe‘. De Sá saturated pipes in a water bath at 50ºC and
evaluated the effect of moisture absorption on numerous mechanical properties. Decreases
of 30% of flexural modulus in the longitudinal direction were observed. Creep tests were
also conducted on the GFRP pipes to determine the long-term circumferential modulus.
There was a strong influence on the initial stiffness and on the viscoelastic behaviour of the
GFRP pipes. Lateral deflections were similar in both dry and wet GFRP pipes. It is
however interesting to note that moisture had no influence on the failure of the GFRP pipes.
Rupture energy and strain at failure of the GFRP pipes under several loading conditions
were determined. This was also concluded by Faria (2005) who examined more exclusively
the failure behaviour of GRP pipes under compressive ring loads.
Perreux and Suri (1997) observed a decrease in viscous properties and glass transition
temperature (Tg). The rate of damage that occurs during fatigue also increases during
repeated progressive loading (RPL) tests. Contradicting these statements Jones et al. (1984)
showed that the rate of damage during fatigue tests of hygrothermally aged composites can
even be smaller than that of unaged composites. A decrease in the strength of the composite
was reported but the effect on fatigue was unchanged. This was also confirmed later by
Selzer and Friedrich (1997) who performed fatigue tests on carbon/epoxy laminates. Their
explanation was simple, carbon fibres generally exhibit good resistance to fatigue and
therefore the effects of moisture on polymers with high fibre content should be
insignificant.
Hao et al. (1992) found that during mode II interlaminar fracture toughness tests, the
critical load and displacement became larger with an increase in the absorbed moisture.
They effectively explained that moisture infuses into polymers; thereby causing the
polymer molecules to separate. The molecules can then easily move past the critical strain
levels, due to the reduction in their secondary bond attraction. This causes plasticization.
Except for the effect on the fibre/matrix interface, Perpelkin (2006) proposed that there is
another mechanism of action due to the exposure of composites to a liquid medium, this is
known as the Rehbinder effect. This effect is visible in the presence of even minute
amounts of surface-active impurities. Surface-active molecules that ‗enter into the region of
12
a growing crack reduce the surface energy of the newly formed surfaces in fracture and
thus decreases the mechanical stress required for crack growth (Perpelkin, 2006).‘ In brittle
bodies, such as composites that are based on thermosets, the Rehbinder effect is particularly
evident but it is also known to effect highly crystalline polyolefins.
The effect on electrical conductivity and resistivity are examined in a subsequent section
2.5.
2.5 Mass-Gain Ratio and Alternative Measuring Techniques
Majority of the studies conducted, estimate the rate of absorbed moisture by periodically
monitoring the weights of the specimens on exposure to different hygrothermal
environments. Tsai et al. (2006) noted that measuring the mass-gain ratio of thin specimens
completely immersed in water is not reliable. The data found from the process of extracting
a wet specimen from water is easily influenced and manipulated by the surroundings.
Firstly, after extraction the surface of the specimen must be wiped off in order to remove
any excess water and laid in the ambient air in order to ensure the remaining surface
moisture had evaporated before being weighed. Once the surface of the wet specimen
becomes dry, it can start to dewater and thereby changing its inner moisture distribution. If
a specimen is thick, the change happens locally and is therefore negligible but this is not the
case for thin specimens.
Other authors have also experienced some difficulty in experimentally determining the
specimen mass gain and have therefore found an alternative. By measuring the dielectric
properties of the ageing material, the mass of the absorbed water can be determined
(Bunsell, 1984). Stone (1969) effectively determined the presence of water at the interface
by measuring the electrical conductivity changes of glass fibres embedded in a polymeric
matrix. The conductivity increases as a result of a conductive layer forming due to the
presence of water. Belani and Broutman (1978) measured the resistivity changes of
carbon/epoxy specimens exposed to environments containing different levels of moisture.
To effectively ensure the elimination of any fluctuations caused by varying pressures of the
connector clamps, the ends of the specimens were coated with a conductive silver paint. It
was observed that the resistance increased with an increase in moisture and the square root
13
of the resistance varies linearly with moisture content. Desorption tests were also conducted
and it was apparent that the change in electrical resistance is reversible and that the material
regained its original properties.
Belani and Broutman (1978) suggested that in the presence of moisture the laminates swell
in the direction transverse to the fibre direction. The contact pressures between the fibres
are affected by the swelling, leading to a change in the length of the conducting path and
thereby increasing the resistivity. Banks et al. (2000) evaluated the influence of moisture
absorption on the permittivity of CFRP at high frequency range (300 kHz to 3GHz) and
also found an increase with increasing moisture content. In the longitudinal direction an
increase of 5% in electrical impedance for every 0.1% of moisture content was noted.
However, in the transverse direction there is a change of only 0.4% for 0.1% of moisture
content. During the initial stage of absorption the change is almost zero and only starts to
increase when voids in the matrix become filled with water.
Similarly to Belani and Broutman (1978), Banks et al. (2002) suggested that the increase in
electrical impedance is due to an increase in mutual inductance between the fibres and
matrix. Abram and Bowler (2005) studied the influence of water vapour during the curing
process on the electromagnetic properties of polyurea/polyurethane-based composites.
There was a substantial increase in the real relative permittivity of samples cured in
different RH environments. ‗The difference is caused primarily by water uptake into the
polymer matrix which alters the dielectric properties of the composite material due to its
strong polar nature and high value of real relative permittivity (Abram and Bowler, 2005).‘
More detailed research is necessary in this area but thus far it can be concluded that
electrical impedance of composite materials are sensitive to moisture absorption.
2.6 Effect of Seawater in Preference to Conventional Methods
Kootsookos and Mouritz (2004) investigated the effect of seawater on the durability of
GRP. The effect of seawater had no superior effect when compared to distilled or de-
ionised water. Seawater still caused the same effects, debonding of the fibre/matrix
interface as a result of swelling and plasticisation of the matrix. Glass/polyester and
carbon/polyester composites were immersed in seawater at 30°C. Gellert and Turley (1999)
14
reported that glass fibres chemically react with water, which causes alkali elements to leak
out. Carbon fibres do not absorb moisture and are therefore resistant to any corrosive
effects of water. If this holds true, then the mass gain curves of these two composites
should be significantly different; with the carbon/polyester curve much higher than the
glass/polyester. However, Kootsookos and Mouritz found that this was not the case,
speculating that the fibres were not solely responsible for the difference in the mass gain
curves. The emulsion sizing agent on the fibre reinforcement appeared to influence the
absorption behaviour. On glass fibres the emulsion size facilitated greater amounts of water
absorption at the fibre/matrix interface. The carbon/polyester interphase absorbed less
moisture and was due to the silane sizing agent. Mode I interlaminar fracture toughness
testing was performed and showed no variation on the property. A decrease of up to 40% in
flexural strength and a considerable decrease in flexural stiffness were found, similar to the
findings of Gellert and Turley (1999). The effects on mechanical properties are thus
equivalent to the ones obtained by the use of distilled or de-ionised water. To the author‘s
knowledge, this thesis is the first study on the influence of moisture on carbon fibre/epoxy
laminates using de-ionised water for exposure to a 100% RH at room temperature.
2.7 Mechanical Adhesion
Perepelkin (2006) effectively explains that the weak spot of fibre composites is found in the
surface of the adhesive contact between the fibres and matrix. The degree of adhesion is an
important aspect as the fracture properties of a composite is determined by fracture of the
matrix and/or destruction of the adhesive contact. It also determines their response to
aqueous and corrosive environments. A composite with a weak interface exhibit high
resistance to fracture but moderately low strength and stiffness. Similarly, composites with
a strong interface have high strength and stiffness but are very brittle. The relationship
between properties and interface characteristics are naturally complex, as other properties,
such as fatigue and creep, are also affected by the interface.
In advanced composites a large amount of interface is present, as the fibre diameter and
inter-fibre distance are both extremely small. Bao and Yee (2002) explained that an open
space at the interface may exist due to inadequate wetting of the fibre by the matrix,
causing fast diffusion in the fibre direction due to the capillary effect. The normalized
15
composite weight gain will be higher than that of the neat resin due to the filling of voids at
the interface. To improve adhesion and wetting, coupling agents and surface treatments
have been used. The rigidity of reinforcing fibres where strong adhesion is present leads to
the restriction on the matrix segmental motions near the interface. This has been verified by
research of supported polymer thin films on silicon substrate (DeMaggio et al., 1997; Lin
et al., 1999). Tsengolou et al. (2006) confirmed the theory presented by Bao and Yee
(2002) that water diffuses rapidly into composites along the fibre-matrix interface if wetting
of the fibres by the matrix is incomplete. They also supported the fact that by improving
adhesion and wetting, this will inhibit the environmental agents to penetrate and destroy the
interface, thereby suppressing subsequent hygrothermal degradation in composites.
2.8 Natural Fibres
The use of natural fibres as an effective alternative for glass fibres in engineering
composites is becoming increasingly important. Although, in this body of work more
conventional fibres1 are looked at, it is necessary to evaluate the knowledge accumulated
through research of moisture absorption of natural fibres. Natural fibres generally have
more disadvantages than conventional fibres including lower impact strength and higher
moisture absorption rates. The latter is of great importance in this study. Natural fibres also
suffer from dimensional changes, thermal instability and micro-cracking (Athijaymani et
al., 2009). A study conducted in order to assess the effect of different fibre loadings on the
absorption of moisture, found that with an increase in fibre content and length there is an
increase in moisture absorption (Bunsell, 1984). The transport of water via micro-cracks,
flow of water molecules through the fibre-matrix interface and diffusion through the bulk
matrix are almost identical in all fibres, and thus the capillarity mechanism is almost
indistinguishable. Decreases in tensile strength of natural fibres are also similar to those of
conventional fibres reported in literature. In dry conditions, an increase of tensile strength
with increasing fibre content is evident, however it is important to note that the decrease in
tensile strength of wet specimens are the same, irrespective of fibre content.
1 Carbon Fibre, Glass Fibre and Boron Fibres.
16
2.9 Thermoplastic versus Thermoset polymers
Epoxies are the most widely used matrix system in advanced composites, however epoxy
resin is most susceptible to moisture absorption (Daniel and Ishai, 1994). Epoxy resins
typically absorb over 4% moisture by weight, where thermoplastic resins absorb less than
1% by weight (Baker et al., 2004). As discussed in section 2.5, thermoset composites can
experience a decrease of up to 40% in a number of their mechanical properties. Conversely,
when exposing thermoplastic composites to similar environments their properties are not
adversely affected. Chen-Chi and Shih-Wen (1991), found that thermoplastic composites,
such as carbon fibre reinforced polyetheretherketone (PEEK/CF, trade name APC-2)
showed excellent retention of mechanical properties even at 80°C, 85% RH.
Polyphenylenesulfide composites (PPS/CF) showed a small decrease at the same
temperature and relative humidity; however this degradation was mainly due to thermal
effects. Similar findings were reported by Matthews and Rawling (1994) and Ma and Yur
(1991), who experimentally confirmed that PEEK, like many thermoplastic matrices, does
not absorb a significant amount of moisture. Even when used in wet conditions at elevated
temperatures as high as 120°C, PEEK still retains its mechanical properties.
2.10 Digital Image Correlation (DIC)
Digital image correlation (DIC) is a computer-based image analysis technique that enables
the measurement of strain and displacement over a virtual grid on a material‘s surface
(Haddadi and Belhabib, 2007). It is a non-contact method as it allows the strain to be
measured without any disturbance to the mechanical response of the material. It is low cost
and the experimental setup is relatively easy.
The technique is based on the comparison of images taken with a digital charge coupled
device (CCD) camera at different increments of the load applied (Dempsey, 2010). Before
testing the specimen must be coated with a random speckle pattern. This is done by
applying a white coat; a point airbrush can then be used to obtain a random speckle. The
quality of the applied speckle pattern has a great influence on the accuracy of the results.
Lecompte et al., (2005) completed extensive research on the quality of speckle patterns for
digital image correlation. The suggestions were used in section 4 of this thesis and therefore
a detailed analysis will not be included here. Other errors that influence the correlation
17
results include: size of the subset, distortion and systematic errors caused by gray-value
interpolation (Haddadi and Belhabib, 2007).
2D DIC utilizes one camera to take images of this pattern on the surface of the specimen.
These images and data are then post processed in order to determine the strains and
displacements (Yaofeng et al., 2007). During the post processing contour plots are
generated. These are useful to determine the areas of interest as any stress concentrations
would be visible.
2.11 Fractography studies
The use of scanning electron microscopy (SEM) as a method of analyzing the fracture
surfaces of composites has become increasingly important. Fractography studies can reveal
the mode of deformation for comparison and the exact mechanical deformation; it is thus
ideal for use in-service to determine the fracture of a real product. SEM is one of the most
versatile instruments available for the examination and analysis of the microstructural
characteristics of solid objects (Goldstein et al., 1981). SEM has a large depth of field; this
allows more of a specimen to be in focus at one time (Schweitzer, 2010). The degree of
magnification is also more controllable, as SEM utilizes electromagnets rather than lenses.
By using SEM, a better understanding of structure-property relations can be obtained.
Analysis on the microstructure characteristics such as fibre shape, diameter and structure
(e.g. crystal size, voids) can help determine the expected mechanical properties of the
material. Fibre dispersion or misalignment in the laminate during manufacture can also be
determined. Misaligned fibres can cause micro-buckling of fibres and is therefore important
(Nakanishi et al., 1997). The fibre-resin system, the mechanisms of the crack nucleation
and propagation and the temperature at which fracture occurred also affects the fracture
surface. Room temperature fracture causes deformation of soft or rubbery phases, while
fracture at colder temperatures causes less deformation. Fracture at colder temperatures
however tends to be less reproducible.
SEM conducted to observe the effect of moisture absorption on the fracture surfaces of
carbon-fibre/epoxy specimens showed that the fibre-matrix interface becomes poor with
increasing moisture content (Selzer and Friedrich, 1995). The effect was observed by
18
comparing micrographs of dry and wet specimens. Fracture surfaces of dry specimens
showed large scale hackling. Failure of the interface is evident at the wet specimens, which
show less hackling, with more bare fibres visible. Pantelakis et al., (2010) observed a
swelling at the fracture surface for wet specimens loaded in tension. This could indicate
extensive delamination and intralaminar cracking. An irregular fracture pattern was
observed in wet specimens loaded in fatigue; specifying a more gradual and less brittle
fracture mode occurred. Another observation that is particularly important is the degree of
fibre pull-out. Fibre ends will be present in the fracture surface depending on the degree of
fibre pull-out. Gilchrist and Svensson, (1995) have established a relationship between the
loading mode and the number of fibre ends found on the fracture surface, and thus will not
be further discussed herein. The degree of fibre pull-out also has a direct relationship to the
strength of the adhesion of the fibres to the matrix. The better the adhesion the more fibre
pull-out and vice versa.
Chapter 3
Theoretical Analysis
19
3 THEORETICAL ANALYSIS
This chapter describes the relevant theory associated with the evaluation of moisture
absorption on composite materials, when exposed to either a humid environment or fully
immersed in water. Section 3.1 outlines Fickian‘s Law of diffusion and derives the
equations necessary to determine the diffusion coefficient. Section 3.2 reviews the
interlaminar shear strength characteristics and the equation required in order to determine
the interlaminar shear strength of the material.
3.1 Diffusion and Fick’s second law
Polymer composites can exhibit both Fickian and Non- Fickian moisture absorption
characteristics with the diffusion process. The former being discussed here. Diffusion in
polymer composites is influenced by a variety of variables such as; loading, fibre
arrangement and interface characteristics. These variables have been thoroughly examined
by Bao and Yee (2002) and therefore will not be repeated here. Using Fick‘s second law,
which is applicable to homogenous and isotropic materials, the experimental data can be
rationalized. This method has been verified as being valid for carbon fibre-reinforced epoxy
resin composites (Shen and Springer, 1975).
Crank‘s (1987) theory of plate diffusion is followed here. It holds for a relatively large and
thin plate of composite material. In the z – direction being the thickness of the material, the
water concentration can be accumulated by the one-dimensional diffusion equation.
(3.1)
Where D is the diffusion coefficient and is considered to be constant in the direction of
diffusion z so that equation (3.1) can be rewritten as:
(0 z L, t > 0) (3.2)
The boundary conditions are:
c = c0 (0 < z < L, t < 0)
c = c∞ (z = 0, L, t > 0)
20
Where t is time; L, thickness of the specimen; z, distance measured from the bottom
surface; subscripts ‗0‘ and ‗∞‘ represent ‗initial‘ and ‗fully saturated‘ states, respectively;
and Dz is the moisture diffusion coefficient in the z-direction.
Equation (3.2) can then be solved and equation (3.3) is established.
∑
{
} {
} (3.3)
The percentage of water absorbed in the composite is defined as follows:
(3.4)
This can be abbreviated as:
(3.5)
Using equations (3.3) and (3.4) and estimating at a specified time t, this can be reduced to
(
) (3.6)
At the initial time t0, the absorbed water is then given by:
(
)
(3.7)
By plotting the percentage moisture content, M against the square root of time, √ the
resulting figure would be:
21
Figure 3-1. Fickian Diffusion Curve (Shen and Springer, 1975; Greene, 2007)
The following equation can then be used to determine the diffusion coefficient from the
experimental data plot (obtained from the slope) and the diffusion mechanism identified.
(
)
(
√ √ )
(3.8)
Where Mm on the graph represents the moisture content at saturation or M∞ in equation
(3.8).
22
3.2 Interlaminar Shear Strength (ILSS)
The interlaminar shear strength (ILSS) is dominated by the matrix and fibre/matrix
interface (Khan et al., 2010). Hull (1981) experimentally confirmed this by observing that
―crack propagation can occur entirely by shear of the matrix without disturbing or
fracturing‖ any of the surrounding fibres. It is thus a measure of the in situ shear strength of
the matrix layer between plies (Daniel and Ishai, 1994).
3.2.1 Equation for calculating the ILSS
The following equation was obtained from Daniel and Ishai (1994) in order to calculate the
interlaminar shear strength of the test specimens. The dimensions needed, can be seen in
Figure 3-2 below.
(3.9)
Figure 3-2. Specimen dimensions
The load at failure initiation (P) is divided by the product of the width of the specimen (w)
and the distance between the notches (l). Units of Pascals (Pa) or Newton per metres
squared (N/m2).
w
l h
Chapter 4
Experimental
23
4 EXPERIMENTAL
This section contains an in-depth explanation of the test methods used to obtain the data
discussed in Chapter 5. This section was imperative in the project, in order to verify
assumptions made and substantiate the results obtained by other researchers. This section
follows a sequence, or an order, in which the experimental studies were carried out. Section
4.1 outlines the material, manufacturing and the relative humidity environment the
specimens were immersed in. Section 4.2 describes the experimental procedure and
apparatus used in order to carry out the ILSS test. Section 4.3 outlines the DIC process and
analysis and finally section 4.4 describes the equipment and sample preparation needed in
order to carry out SEM on the fracture surfaces.
4.1 Material
4.1.1 Test specimens
Two symmetric laminates, with [08]s and [06 902]s configuration using HTA/6376, were laid
up and cured in an autoclave at 180°C for two hours, in accordance with Hexcel
recommended curing cycle. Using a diamond blade saw, the laminates were then grooved
and cut to manufacture single lap joints, with overall dimensions of 12.5mm x 179mm x
2mm. The notch depth of 1mm, width of 2mm and an overlap area of 5mm, are shown in
Appendix B. Actual dimensions of each specimen were measured using a Baty® R400XL
shadowgraph projector with a Metronics® Quadra Check 2000 monitor (Figure 4-2). For
each specimen the average of three measurements per dimension was used. A total of
twenty one specimens of each lay-up were manufactured and tested. Information on the
fibre treatment for improved fibre-matrix adhesion was not available. The average fibre
volume fraction (Vf) was 59.2%.
4.1.2 Conditioning and Specimen Exposure
The cut surfaces were carefully polished in order to remove possible edge damage effects;
due to the cutting operation. The specimens were then dried in an oven at 120°C for 60
minutes. The dry specimens were stored in a dessicator to control the relative humidity and
the wet samples immersed in a bath of de-ionized water and kept at room temperature (19 ±
2°C) in a sealed plastic container. Exposing the specimens to a 100% RH environment, by
fully immersing them in water, is the worst possible moisture attack (Selzer and Friedrich,
24
1995). All samples were orientated in a vertical direction to permit water diffusion to occur
from both sides of the samples during the process of water absorption. After two time
periods - two and four months, the specimens were subjected to interlaminar shear strength
tests.
4.1.3 Measurements
The specimens underwent weekly measurements where the specimens were quickly
removed from the container, wiped down with a microfibre cloth, in order to remove any
excess water or surface condensation, and weighed on an Explorer® Analytical Balance
(Figure 4-1) with a resolution of 1 x 10-4
g. For each measurement a minimum of three
replicates were used. To ensure minimization of any discontinuity in the moisture
absorption process, the weighing process was completed in a relatively short time frame
and the effect of this removal on weight gain determination was negligible.
The thickness and notch width of the specimens were measured using a Baty® R400XL
shadowgraph projector (1) with a Metronics® Quadra Check 2000 monitor (2) (Figure 4-
2). This process was repeated for the entire immersion period. All specimen weight gain
values can be found in the corresponding tables in Appendix D, where the mass gain due to
moisture absorption is measured in terms of the percentage of the dry mass of the material.
Figure 4-1. Explorer Analytical Balance
25
Figure 4-2. Shadowgraph Projector
4.2 Interlaminar Shear Strength (ILSS) Test
A standard test method (double-notch) for interlaminar shear strength of the material was
carried out. To avoid out-of-plane bending a clamp (Figure 4-3) for the interlaminar shear
test was manufactured, adapted from ASTM Standard D3846-08. A detailed drawing of the
clamp is illustrated in Appendix C. This test method only requires a small amount of
material and this allowed for several specimens to be tested which provided a reliable
statistical description of the data. Testing was performed under three conditions: Dry,
withdrawal I (2 months) and withdrawal II (4 months). Seven specimens of each condition
and lay-up configuration were tested. The tests were performed at room temperature in a
laboratory air environment. When testing the wet specimens care had to be taken in order to
ensure the environment did not affect the specimens. The specimens were removed 30
minutes prior to testing and stored in a plastic bag to minimize interference in the moisture
content and were then immediately tested. During the testing procedure, a distinct
difference between the dry and wet specimens was observed.
2
1
26
Figure 4-3. Clamp used in ILSS Testing
4.2.1 Experimental Apparatus and Procedure
The experimental tests were performed using a Tinius Olsen H25KS mechanical testing
machine. The experiment was set up as shown in Figure 4-4 using a 25kN Load Cell (1).
The specimen (2) was placed in the clamp (3) so that it is flush with the base and centred.
The screws were torque finger tight. Using the control panel (4) the load and extension was
zeroed. The specimen assembly was gripped at both ends using serrated wedges (5). The
specimen was then tested in increments of 1mm/min at the cross head. Upon failure, the
maximum load carried by the specimen during the test was recorded. A force against
extension graph was plotted. After failure occurred the specimens were unloaded at a
constant cross head rate of 25mm/min. The interlaminar shear strength was determined
using equation (3.9) and compared with published values for the material.
27
Figure 4-4. Tinius Olsen H25KS Model
4.3 Digital Image Correlation (DIC)
The three main steps in the correct usage of DIC include; (1) Acquisition, which involves
the surface preparation of specimens and correct illumination. (2) Interrogation, relating to
the correlation and estimation process. (3) The validation or the analysis of the results.
Preparation of Specimens
The area of interest on the specimens was sprayed using a coat of acrylic white paint. Using
a Badger Airbrush model 200-3, a finely dispersed, non-uniform pattern coat of black was
then applied. A fully prepared specimen can be seen in Figure 4-5.
1
Lo
ad
Cel
l
5
Lo
ad
Cel
l
3
Lo
ad
Cel
l
2
4
Cel
l
28
Figure 4-5. Speckled Specimen
Equipment
A high magnification camera (1) was attached to a horizontal rail (2) using mounts (3)
(Figure 4-6). The tripod (4) setup was positioned in front of the Tinius Olsen. Two LED‘s
(5) were connected and used as gated light sources. The procedure in section 4.2.1 was then
followed to prepare the test. The 2D DIC was started simultaneously with the Tinius Olsen.
The loading was continued until failure occurred. The DIC was then stopped and the test
specimen was unloaded. Before each test, the focus of the camera was adjusted in order to
ensure a sharp, focused view of the speckle pattern. In the Da Vis 7.4.0.99 software, the
number of images to capture was set to 2500 and the frequency of the image acquisition
was set to 3Hz. This procedure was carried out on 3 specimens of each lay-up configuration
for dry and withdrawal I time periods.
29
Figure 4-6. Strain Master experimental setup (adapted from La Vision, 2010)
Validation and Analysis
Using the strain master DIC system, the movement of the surface pattern applied to the
specimen under stress was traced. This was used to determine the strain and displacement
in the x- and y-direction, εxx, Vx, εyy and Vy respectively.
5 1
2
3
4
30
4.4 Fractography Studies
All specimens tested were examined visually and with the aid of a TRAVELER Universal
Serial Bus (USB) Microscope (1.3 Megapixel). Any cracks or delamination which occurred
during the handling or testing of the specimens were also recorded.
Thorough investigations on the effects of moisture on the fracture surfaces of the specimens
were examined by Scanning Electron Microscopy (SEM). The specimens had to be
prepared with a conductive coating prior to imaging. Using Argon gas, the specimens were
sputter coated with gold in a vacuum chamber. Using a Deposition Rate against Deposition
Current graph, suitable values were selected for the specimens. The specimens were then
mounted on an aluminium stub for analysis. A JEOL JCM 5700 (Figure 4-7) was used at
magnifications ranging from x100 to x3000.
Figure 4-7. JEOL JCM 5700 (www.jeolusa.com)
Chapter 5
Results and Discussion
31
5 RESULTS AND DISCUSSION
This section analyses the results from the present work. The analysis begins with Fickian
diffusion and specimen weight gain and its subsequent effects on the volumetric expansion
of the laminates. The effect of moisture on the ILSS is discussed in section 5.2.
Displacement and strain contour plots obtained using Digital Image Correlation (DIC) is
examined in section 5.3. The findings of the investigation into the fibre/matrix interface
using Scanning Electron Microscopy (SEM) are discussed in section 5.4.
5.1 Fickian Diffusion and Specimen Weight Gain
In order to ensure that saturation of the specimens occurred, the key factors affecting
diffusion were optimized. Selzer and Friedrich (1995) and Hao et al. (1992) demonstrated
that specimens absorbed more moisture at low temperature/high relative humidity than at
high temperature/low relative humidity conditions. This was taken into account and due to
the time constraint and the inability to control the water temperature; the specimens were
immersed for a maximum of four months in a 100% RH environment. The specimen
dimensions and laminate configurations were also optimized in order to guarantee
saturation. The thickness was reduced by using the smallest number of plies, however still
maintaining a sufficient thickness in order to ensure good ILSS test results (section 5.3.4).
By following the weekly weigh-in procedure outlined in section 4.1.3 and by using
equation (3.4) and (3.5), the moisture gain percentage was plotted against the square root of
time (Figures 5-1 and 5-2).
The results shown in the subsequent graphs were averaged from the measurements of 7
specimens. The curves have not been fitted and no points have been excluded. Some scatter
of the data points were observed during the accumulation of the moisture absorption data.
This can be due to a number of reasons; the variation of voids on the different specimens,
as they were cut from different parts of the panel. The fibre dispersion was also assumed to
be the same within each specimen; however from the SEM (section 5.4) it was evident that
this was not the case.
32
Figure 5-1. Moisture content (w/w %) - [08]s configuration
Figure 5-2. Moisture content (w/w %) - [06 902]s configuration
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
0 2 4 6 8 10 12
Mo
istu
re g
ain
pe
rce
nta
ge (
Wga
in %
)
Sq. root time(t1/2) days
Withdrawal I
Withdrawal II
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 2 4 6 8 10 12
Mo
istu
re g
ain
pe
rce
nta
ge (
Wga
in %
)
Sq. root time(t1/2) days
Withdrawal I
Withdrawal II
33
As mentioned earlier, due to the time constraint on the immersion time, the specimens were
only immersed for a maximum of 4 months. As evident from Figures 5-1 and 5-2, this only
allowed for the first diffusion stage to be documented. The second stage, which is
dominated by the deterioration and relaxation processes, could not be assessed. During the
initial stage of immersion the weight of the specimens increased rapidly. The rate of weight
gain decreased with time; however the average slope remained constant. This verified Shen
and Springer (1975) findings that carbon fibre-reinforced epoxy composites follow Fickian
diffusion behaviour. This also indicates that at 4 months (withdrawal II) the specimens,
although closer to saturation than at 2months (withdrawal I), had not reached a state of full
saturation upon withdrawal. On average the room temperature varied from 19°C ± 2, while
the water temperature varied from 19°C ± 3. One week both temperatures fell significantly
below the average, with the room temperature being 14°C and the water temperature as low
as 11°C. This affected the rate of diffusion of the specimens; a direct relationship between
the temperature and moisture uptake was established, with a decrease in temperature
causing a lower weekly absorption rate. This is illustrated in Appendix D, where the
specimen weight gain values, room and water temperature data is presented as well as
additional notes.
The maximum mass content varied slightly depending on the lay-up configuration. The
maximum mass content was higher for the [06 902]s specimens (Table 5-1). This could be
explained by the residual stress that developed in the laminates during the cool down period
of the material after curing. The residual stress is a function of a number of properties
including stacking sequence and ply orientation (Hull, 1989). Subsequently, the residual
stress is higher if the thermally anisotropic plies are oriented along different directions. The
residual stress in the [06 902]s specimens was thus higher than that in the [08]s specimens.
According to Perlevliet et al. (1996), the higher the residual stress, the higher the moisture
uptake. The effect of residual stress in the laminates is discussed further in section 5.2.
34
Table 5-1. Moisture content (w/w %)
Exposure
Time
2 months 4 months
[08]s [06 902]s [08]s [06 902]s
Moisture Gain 0.626% 0.762% 0.784% 0.906%
The moisture level obtained compared well with those reported in literature. Matthews and
Rawlings (1994) predicted that epoxy resins absorb between 1% and 10% by weight of
moisture, so a typical composite with 60% fibre volume fraction (Vf) will absorb around 0.3
to 3% moisture. The average Vf for HTA/ 6376 was 59.2% and therefore the moisture level
obtained compared well with those obtained from other authors using similar Vf ratios.
As previously stated, this thesis has studied moisture absorption from a macroscopic point
of view. Whereby the fibre/matrix interface is examined and the overall effects on the
lamina are considered. The work obtained here is a good starting point for the design and
manufacturing considerations necessary when selecting composite material for certain
applications. To effectively consider these results for industry applications the differences
are important to note. It is important to note that both faces of the specimens were exposed
to de-ionized water, where in-service conditions only expose one face to the atmospheric
environment. In addition, the specimens did not have a protective coat and thus different
paint schemes on aircraft could have an effect. The specimens were exposed to a constant
100% RH environment for the specified time period. In-service, the level of moisture in the
material is known to fluctuate as the material may dry during flight where the humidity is
low. Due to this, the time to reach saturation or equilibrium will be longer. Materials that
are fully exposed or shaded can lose mass due to erosion and ultraviolet (UV) degradation
of surface matrix or paint layers. There are thus a number of variables that have to be
considered, including different exposure conditions with the respect to where the aircraft is
operating. Therefore, the results illustrated in this thesis represent an usually severe
condition. Typical equilibrium moisture contents for epoxy-based composites were found
to range from 0.7% to approximately 0.9% after long-term outdoor exposure (Hull, 1981;
Vodicka et al., 1999; Zagainov and Lozino-Lozinski, 1996). The percentage achieved in
this short-term constant exposure study fell within this region with [08]s specimens having
values of 0.78% in specimen weight gain and the [06 902]s specimens having values of
0.9%. Another key parameter is the specimen thickness. The specimen thickness was
optimized in this study in order to maximise the rate of diffusion. In-service panel
35
thicknesses and lay-up configuration may differ considerably. Although, the zero
dominated lay-up configurations used in this study is representative of lay-ups suitable for
composite aircraft wing skins (O‘Higgins et al., 2004).
5.2 Volumetric Expansion
As well as the weekly weigh-in, the specimen dimensions were closely monitored with the
distance between the notches, thickness and width of each specimen noted (Appendix D).
In the initial stage of the immersion, it was found that even with an increase in the total
mass there was no overall volume change, this is due to the fact that water may occupy pre-
existing space in the material first, therefore resulting in no overall volume change during
the initial stage of diffusion. On the other hand, water may force its way into the material
by opening pre- existing cracks and structural imperfections thereby leading to an increase
in the total mass and an increase in the overall volume. The overall volume change for both
configurations can be seen in Table 5-2.
Table 5-2. Volume Change (%)
Specimen Configuration
Volume Change (%)
Withdrawal I Withdrawal II
[08]s 8.7% 10.2%
[06 902]s 7.2% 8.7%
It is important to note that the volume change in all directions was not equal. The greatest
dimensional change occurred in the laminate thickness, at the region between the notches.
The main reason for this is that in the area between the notches, diffusion not only occurs
through the surface of the specimen but also diffuses into the region in between the notches,
thereby causing the rate of diffusion in that area to be the highest. The fibres absorb little or
no moisture and it is mostly only the resin matrix that absorbs moisture (Matthews and
Rawlings, 1997; Daniel and Ishai, 1994; Cervenka et al., 1989). The absorbed water softens
the epoxy resin, causing it to swell, therefore increasing the laminate thickness. The volume
change was found to be in line with Belani and Broutman (1978), who suggested that, due
to the presence of moisture the laminates swell in the direction transverse to the fibre
direction.
36
Some deviation between the moisture and volume change between specimens were also
found (Appendix D). This could be due to a number of different types of manufacturing
defects such as voids, delaminations, resin starvation, resin-rich pockets, damaged fibres or
fibre-matrix debonding (Hyer, 1998). The specimen weight gain and volume change also
fluctuated from week to week. This could be due to the weight measurement process, as the
data found from extracting a wet specimen from water is easily influenced and manipulated
by the surroundings (Bunsell, 1984; Stone, 1969). Great care was taken to ensure minimal
interference, by using a weighing scale with a resolution of 1 x 10-4
g and using a minimum
of three replicates of each measurement. During the process, the specimens were quickly
removed from the container, wiped down with a microfibre cloth, in order to remove any
excess water from the surface. However, once the surface of the wet specimen becomes
dry, it can start to dewater and thereby changing its inner moisture distribution. If a
specimen is thick, the change happens locally and is therefore negligible however this is not
the case for the thin specimens used in this study (Tsai et al., 2006).
5.3 Interlaminar Shear Strength (ILSS)
The main objective of this thesis was to investigate the effect of moisture on the
fibre/matrix interface of carbon fibre/epoxy laminates and consequently its effect on the
mechanical properties. It is well known that the fibres do not absorb moisture but only the
resin. Therefore it is the strength of the fibre/matrix interface which needs to be tested. A
simple tensile test would not suffice, as it measures the strength of the fibres. The ILSS test
was therefore chosen. The ILSS is a matrix dominated property and is dependent on factors
such as moisture and temperature and is ideal for the analysis (Daniel and Ishai, 1994;
Khan et al., 2010). The visible changes in the fibre/matrix interface will be discussed in
section 5.5.
5.3.1 ILSS Results
Table 5-3 shows a comparison between the ILSS values for dry, two month (Wet I) and
four month (Wet II) withdrawal specimens. The ILSS values are seen to increase over time
when exposed to moisture. In literature it has mostly been reported that moisture causes
degradation in mechanical properties; however, when examining these reports closely it is
evident that this only occurs when laminates are exposed to moisture at elevated
37
temperatures. Matthews and Rawlings (1994), Choi et al. (2001) and Akbar and Zhang
(2008) also validated this with their research and found a decrease in ILSS only occurs at
elevated temperatures.
Table 5-3. ILSS values
Lay- up
Configuration
Interlaminar Shear Strength (MPa)
Dry Wet I Wet II
[08]s 36.1 ± 2.9 37.5 ± 2.6 40.2 ± 3.30
[06 902]s 19.8 ± 0.9 23.0 ± 1.8 23.2 ± 1.19
Table 5-4 shows the percentage increase in ILSS values as a function of exposure time. The
influence of moisture is predominant in the [06 902]s laminates, with increases of up to
18.73% after four month immersion. The [08]s laminates obtained increases of almost half
the percentage of the [06 902]s laminates, with a maximum value of 11.3% after four month
immersion. The effects of moisture on the mechanical properties of composite materials
have been well documented in previous literature, however the magnitude of the effect is
not agreed upon. The results found in this thesis compared well to published values by
Vodicka et al. (1999), who confirmed that at temperatures below the Tg, the presence of
moisture increases the ILSS by about 15%.
Table 5-4. ILSS percentage increase values
Lay-up Configuration Withdrawal – 2 months Withdrawal – 4 months
Percentage Increase (%)
[08]s 3.76 11.30
[06 902]s 17.65 18.73
From the results it is evident that the interlaminar shear strength of a material is a function
of the laminate stacking sequence (Daniel and Ishai, 1994). The [08]s laminates have higher
ILSS values than the [06 902]s laminates. However, the [06 902]s laminates obtained a higher
increase in ILSS due to the absorbed moisture. The design criteria for certain applications
can thus be fulfilled by controlling the stacking sequence of the laminates.
38
5.3.2 Stress State
The interlaminar shear strength of a resin matrix is dependent on the stress concentration
effects associated with the presence of fibres and voids and on the strength of the interfacial
bond (Hull 1981). Therefore, in order to effectively explain the phenomena of the ILSS
increase over time due to moisture absorption, two factors have to be considered. (1) The
stress state in the material before immersion and (2) the stress state in the material after
immersion in de-ionized water.
Before immersion
A laminate is considered to be stress free at a certain temperature during the curing process.
This temperature is normally taken as the glass transition (Tg) temperature of a polymer
matrix. When the laminate cools down to room temperature after being cured at an elevated
temperature, residual stress develops in the laminate (Lubin, 1998). Similar to hygrothermal
effects, residual stresses are a function of certain parameters including ply orientation,
stacking sequence and fibre volume ratio (Daniel and Ishai, 1994). Subsequently, the
residual stress is higher if the thermally anisotropic plies are oriented along different
directions (e.g. [06 902]s configuration laminates). This can also be verified by looking at the
[06 902]s moisture gain results. According to Perlevliet et al. (1996), the higher the residual
stress, the higher the moisture uptake. This was verified in section 5.1 with the [06 902]s
laminates absorbing more moisture than the [08]s laminates. The effect of curing cycle on
the development of residual stresses has been studied by a number of researchers and will
thus not be included herein (Kawata and Akasaka, 1981; Parlevliet et al., 2006). The
residual stress in the laminate is non uniform and this leads to stress concentrations
developing in the laminate. The cut notches also caused some stress concentrations at the
notch root vicinity (Zagainov and Lozino-Lozinski, 1996).
After immersion
The matrix expands or swells during moisture absorption and this leads to a change in the
stress state in the material. The swelling of the matrix has caused the stress (residual stress
and stress concentrations due to the notches) to distribute over a bigger volume of the
material, subsequently causing the laminate to fail at a higher load. The stress and strain
fields within the material also changed due to the mismatch in moisture-induced volumetric
expansion between matrix and fibres, as the epoxy matrix absorbs a significant amount of
39
moisture, where the fibres absorb little or no moisture (Akbar and Zhang, 2008; Selzer and
Friedrich, 1995).
The effect of the redistribution of the stress (residual stress and stress concentrations due to
the notches) is only a possible explanation and a more precise analysis of the effect on the
residual stress is necessary.
5.3.3 Flexibility of Resin
An important observation was that when the specimens were tested, the extension (or
elongation) of the specimens were higher with an increase in immersion time. This can
clearly be seen on the Force against Extension graphs (Figure 5-3 and 5-4). With an
increase in exposure time, the increase in the attainable load is coupled with higher
extension values. The higher extension values are mainly due to the softening of the resin
with an increase in moisture content (Selzer and Friedrich, 1997; Matthews and Rawlings,
1994). This was also observed by Hull (1981) and Hamerton (1996) who explained that
moisture affects the flexibility of the epoxy resin, reducing the basic hardness and rigidity,
thereby also decreasing the brittleness and increasing the ductility. This would also mean
that the more the specimens absorbed water, the more the stiffness decreased and the
toughness increased. Plasticization of the matrix is also a contributing factor to the increase
in ILSS values. Moisture infuses into the polymer; thereby causing the polymer molecules
to separate. The molecules can then easily move past the critical strain levels, due to the
reduction in their secondary bond attraction. This causes plasticization of the matrix and
would result in a lower glass transition temperature Tg (Hao et al., 1992; Huang and Sun,
2007).
40
Figure 5-3. Force against Extension [08]s
Figure 5-4. Force against Extension [06 902]s
0
500
1000
1500
2000
2500
3000
3500
0 0.5 1 1.5 2
Forc
e (
N)
Extension (mm)
Dry
Wet I
Wet II
0
200
400
600
800
1000
1200
1400
1600
0 0.2 0.4 0.6 0.8 1 1.2
Forc
e (
N)
Extension (mm)
Dry
Wet I
Wet II
41
Table 5-5 and 5-6 illustrate more exact values including the standard deviation between the
load and extension values for both laminate configurations. It is evident that the increase in
ILSS is directly coupled with the increase in elongation. The increase in elongation is
higher for the [06 902]s specimens with an increase of 4%, compared to an increase of 2.7%
for the [08]s specimens.
Table 5-5. [08]s Specimen - Load and extension values
[08]s specimen Load (N) Extension (mm)
Dry 2336 ±195 1.402 ±0.19
Wet I 2553 ±193 1.442 ±0.22
Wet II 2687 ±224 1.445 ±0.15
Table 5-6. [06 902]s Specimen - Load and extension values
[06 902]s specimen Load (N) Extension (mm)
Dry 1311 ±121 0.94 ±0.20
Wet I 1477 ±104 0.98 ±0.05
Wet II 1484 ±74 0.98 ±0.24
The increase in extension values does not mean a subsequent increase in the elastic
modulus (E). The elastic modulus can either be reduced or could even remain unaffected
(Akay et al., 1997). A decrease in E can clearly be seen in Figures 5-5 and 5-6, where the
Stress against Strain was plotted. The elastic modulus is determined by the slope of the
graph. With an increase in immersion time, an increase in elongation values is found with a
subsequent decrease in elastic modulus. As discussed previous, moisture has the effect of
flexibilising the epoxy resin, reducing the elastic moduli (Hull, 1989). It is therefore
important to note, that while an apparent increase in ILSS values are found other
mechanical properties degrade due to the absorbed moisture.
42
Figure 5-5. Stress against Strain [08]s specimens
Figure 5-6. Stress against Strain [06 902]s specimens
0
5000000
10000000
15000000
20000000
25000000
30000000
35000000
40000000
45000000
50000000
0 0.5 1 1.5 2
Stre
ss (
N/m
^2)
Strain
Dry
Wet I
Wet II
0
5000000
10000000
15000000
20000000
25000000
0 0.2 0.4 0.6 0.8 1 1.2
Stre
ss (
N/m
^2)
Strain
Dry
Wet I
Wet II
43
Reversibility/Irreversibility
The reversibility/irreversibility of the effects on the mechanical properties has not been
experimentally investigated in this thesis, however it is worth mentioning. The most
deleterious effects on stiffness and strength are produced by a combination of elevated
temperatures and high moisture concentration. It is known that only at high temperatures,
the effects on the mechanical properties would be irreversible (Selzer and Friedrich, 1997).
Akbar and Zhang (2008) found that the water absorbed by the epoxy laminates at low
immersion temperatures (≤ 20°C), causes reversible plasticization of the matrix. However,
when combined with temperature effects, these factors cause significant changes in the
matrix toughness which would be irreversible. Similarly, Matthews and Rawlings (1994)
and Khan et al. (2010) proposed that the flexibility of the resin and the decrease in the
elastic modulus values will return to its original value, when the environmental conditions
change and the moisture diffuses out. Recommendations for future research in this area are
discussed in more detail in section 6.2.
5.3.4 Limitations and constraints during ILSS testing
The ILSS test had some limitations; however, the non-expensive method and the
reproducibility of the results proved to be an accurate measure of the integrity of the
fibre/matrix interface. The principal criticism of the test is that severe stress concentrations
are induced in the specimen at the notch root vicinity, making the determination of the
shear strength questionable. Another limitation is that the shear modulus is not obtained.
Tinius Olsen
The Tinius Olsen was used to carry out the ILSS tests. Some slippage of the wedge grips
occurred particularly at the start of the test. This can be seen in the obtained Force against
Extension graphs (Appendix E). Perfect vertical alignment between the grips was also
found to be difficult during the testing procedure. Misalignment of the specimens in the
grips could also have occurred. This caused some scatter in the results obtained; however
this is not likely to be the governing factor, as the misalignment would not be repeatable.
Deviation from linearity on the graphs could also be due to the properties of the resin (Hull,
1989).
44
During testing of the [06 902]s laminates, there was a difficulty in determining the exact
strength, as the complete failure of the laminate was preceded by fracture of individual
laminae. This was evident at around 800-900 Newtons, where a ‗cracking noise‘ was heard.
It is therefore important to note, that while the laminate can sustain an increasing load,
incipient failure has already occurred.
Effect of Notch depth
During experimentation it was evident that the double notch shear test is very sensitive to
the accuracy of the depth of the notches. According to Shokrieh and Lessard (1998),
bending stresses will occur in the gauge area if the depth of the notch is overcut or more
than half the specimen. Similarly, compressive stresses will occur in the gauge area, if the
depth is undercut or less than half the specimen. During manufacture it was very difficult to
control the notch depth and consequently, some scatter in the results was found. It was
necessary to find a suitable method in order to eliminate any points that were out of scope
and a statistical analysis was used in order to eliminate this. The lay-up configuration also
needed to be considered due to the limitations of the double-notched shear test. As a tensile
load applied to a double-notch specimen with a 90° lay-up would result in a tensile matrix
failure prior to failure in interlaminar shear (Shokrieh and Lessard, 1998). A [06 902]s
configuration was used and the experiments showed that the failure for this configuration
occurred between the 0° and 90° lay-up.
Thickness of Specimen
Shokrieh and Lessard (1998) also suggested that in order to complete a better shear test, the
number of plies should be as high as possible. However, due to the difficulty in
manufacturing the specimens, as a thicker lay-up is more prone to human error in the
alignment of the plies and the constraint in exposure time, more than 32 plies would not
have been feasible. Less than 16 plies would also be undesirable due to the sensitivity of
external effects including out-of-plane deformation.
45
Statistical Analysis
Three approaches were used in order to eliminate any results that fell outside of the range
of data. Initially, an Analysis of Variance (ANOVA) approach was used in order to
determine whether the means of the groups were all equal. However, after closer
examination, too many variables were present such as the effect of notch depth, length
between the notches and the width of the specimen. An analysis of the variables affecting
the ILSS results was thus conducted on the seven specimens for each lay-up configuration
and for each immersion period. The ILSS results were examined and the outliers identified.
As the specimens were clearly marked, each outlier and corresponding specimen was then
looked at collectively.
Carbon-fibre reinforced epoxy laminates, or composite laminates in general, comprise of
mechanically dissimilar phases. Therefore, depending on the type of mechanical test,
different failure modes will occur. When the matrix or fibre/matrix interface is tested, such
as the tests conducted in this thesis, failure normally occurs by matrix cracking or shearing
of the fibre/matrix interface. Fibres are normally stiff and brittle and this results in fibres
rupturing in tension or buckling in compression (Hull, 1981; Hart-Smith, 2004). The
fracture surfaces of the specimens therefore had to be examined for specimens with severe
fibre pull out or breakage. This would indicate that during the ILSS test, the fibres might
have taken the load and therefore the values would be higher. This would signify that pure
shear did not occur and the values will therefore be invalid and could not be included in the
analysis. A direct relationship was established with the [08]s specimen outliers and the
degree of fibre rupture or breakage. Specimens that had significantly higher values were
correlated to a higher degree of fibre breakage. As mentioned previous, the double-notch
shear test is very sensitive to the accuracy of cutting the notches (Chiao et al., 1977).
Specimens with notches overcut or undercut were also identified and there corresponding
values examined. Specimens with notches undercut had lower values. Shokrieh and
Lessard (1998) explained this by illustrating that undercutting causes higher positive zz
inside the notch location leading to premature failure. Failure did not occur at the interface
between the two layers and therefore the ILSS test was invalid. After eliminating the
outliers, a standard statistical analysis was used whereby the standard deviation and mean
average between the groups were determined (Appendix E).
46
5.4 Digital Image Correlation (DIC)
The evaluation of the displacement and strain in the region in between the notches were of
focus during the analysis. This data was collected and analysed using various tools from the
Da Vis 7.4.0.99 software (Section 4.3).
It was assumed that the best approach was to start the analysis at the specimen
displacement in the x- and y-direction, as certain criterion was expected. Minimal to zero
displacement in the x-direction (Vx) was detected this is due to the clamp and the Tinius
Olsen wedge grips (Figure 5-7).
(a) (b)
Figure 5-7. Wet I [06 902]s x-displacement (a) At failure (b) After failure
Figure 5-8 (a) and (b) present the maximum and minimum displacement in the y-direction
(Vy) during loading and at failure. The plots indicate that the area of maximum positive Vy
occurred at the right hand edge of the specimen. This was as expected; as the specimen was
gripped in serrated wedges with the left hand side of the specimen underneath the notch
held stationary as the right hand side moved up as shear occurred. The left hand side should
therefore show minimal displacement (0.325mm) with the maximum value at the right hand
side of the specimen (0.6mm).
47
(a) (b)
Figure 5-8. Dry [08]s specimen y-displacement (a). Before failure (b) At failure
The dry [06 902]s specimens obtained displacement values similar to that of the dry [08]s
specimens (Figure 5-9).
(a) (b)
Figure 5-9. Dry [06 902]s specimen y-displacement (a). Before failure (b) At failure
48
Figure 5-9 verified the problems predicted by Shokrieh and Lessard (1998) discussed in
Section 5.3.4. The double notch shear test is very sensitive to the accuracy of the depth of
the notches. The notch was overcut at one side of the specimen; this caused the laminates to
shear but this did not occur in the mid plane of the specimen as intended. This also verified
the prediction that for a specimen with a [06 902]s configuration, failure occurs between the
0° and 90° plies.
Strain in the y-direction (εyy)
Contour plots of the strain fields were plotted. The contour plots are useful to determine the
areas of interest (i.e. stress concentrations). The size of the specimen (Section 4) only
allows for a small load to be taken and therefore a relatively small strain value to occur.
These values could thus easily go undetected. The εyy plots give a good indication of the
strain pattern but they are mainly for visualisation and approximation purposes (Figure 5-
10). They are not suitable for detailed analysis.
Figure 5-10. Dry [08]s specimen - Strain Exx – (a) At start of load (b) At failure
(a) (b)
49
At the start of the load, some strain in the y-direction can be seen. The εyy contour plots
exhibits a reasonable uniform distribution. There are some inconsistencies present but the
overall distribution of the strain values are small, between 0.006μ and 0.011μ, and was
therefore assumed to be negligible.
Strain in the x-direction (εxx)
The dry [06 902]s specimen showed a slightly higher value of εxx at the start of the load,
when compared to a wet specimen of the same lay-up configuration. The strain values for
both specimens in the x-direction were small (< 0.025ε).
(a) (b)
As discussed in section 5.2, when testing the [06 902]s specimens, failure of individual
laminae occurred before failure of the laminate. 2D DIC was consulted in order to establish
if this was evident during the analysis, however this could not be detected. There were
numerous reasons for not detecting the failure of the individual laminae. Foremost, DIC
only detects strains and displacement of the surface of the specimen and incipient laminate
failure was likely to have occurred at the middle laminae of the specimens. Another
Figure 5-11. [06 902]s Specimen - Strain in the x-direction (a) Dry specimen (b) Wet specimen
50
limitation of using the 2D DIC system was that it cannot account for any out of plane
displacement and hence εzz could not be assessed.
Errors relating to DIC
The DIC system is extremely sensitive to effects of the surrounding environment. Some
precautions were taken in order to eliminate this:
The system was regularly calibrated in order to ensure that the best results were
obtained.
Extreme care had to be taken in order to ensure that during the ‗specimen rotation‘
the camera and tripod set-up had not moved slightly.
Dust particles were evident on the lens; it was therefore removed and cleaned
during testing however some particles still remained. This caused some features in
the obtained images.
Care was taken in preparing the specimens, in order to ensure a suitable level of
contrast and to ensure good quality of the speckle pattern. This could have also had
an influence on the results.
A high resolution of 64x64 megapixels was used, which gave a precision of up to
0.01 per pixel for any 2D vectors calculated.
An extra light source was added to ensure uniform and sufficient lighting covered
the whole zone of interest on the specimen.
As discussed earlier, there was some misalignment in the grips. Assuming this was
negligible may have also affected the results.
51
5.5 Fractography Analysis
Nakanishi et al. (1997) and Perepelkin (2006) effectively explained that the microscopic
interfacial properties of a laminate determine its macroscopic mechanical properties. This
section was therefore imperative in order to understand the effect of moisture on the
interface of carbon-fibre reinforced epoxy laminates and subsequently the increase in ILSS
values. This was completed by the use of optical microscopy and scanning electron
microscopy (SEM).
Optical Microscopy
Some delamination of the surface of the laminates was noted during the weekly weigh-ins.
This is as a result of swelling stresses in the matrix due to the absorbed moisture
(Pantelakis, 2010). The specimens that experienced delamination were noted and the ILSS
values were examined after testing. The delamination was minor and had no effect on the
ILSS of the specimens. The lower magnification (x10) micrographs were taken using an
optical microscope.
Scanning Electron Microscopy
Various magnifications were used ranging from x100 to x3000. At the lower value
magnifications there were no visible differences (Appendix F). Magnifications at x1000
and x2000 at 10μm showed the best distinction between wet and dry specimens and
consequently these micrographs are the focus of analysis here. The main conclusions that
can be drawn from the analysis are outlined. The degree of alignment was assumed to be
the same in each specimen; however from the SEM this was clearly not the case. It was
evident that the fracture surfaces were greatly influenced by the amount of exposure, as this
determined the amount of failure present at the matrix. For the dry specimens, where the
bonding between the fibre and resin was good, the surface was fairly smooth. The texture
of the fracture surfaces varied depending on the exposure period. The difference from a
brittle matrix and a ductile matrix is clearly evident. These observations are discussed in
greater detail below.
52
Figure 5-12 depicts the fracture surface of a dry specimen of a [08]s laminate. The [08]s
laminate showed excellent fibre dispersion. The fibre distribution was uniform and the
matrix-fibre bonding good. The dry specimen exhibited brittle fracture (Figure 5-13). There
are no porosity cracks visible, indicating essentially a void free laminate (Botelho, 2006).
Fibre-pull out was observed at the dry specimens (Figures 5-12 and 5-13); this is due to
good bonding between the fibres and the resin. This effect was less, but better than what
was anticipated, at the wet specimens (Figure 5-15). This means that even in a wet state the
specimens still maintained good adhesion between the fibre and matrix. This minor
decrease was due to the moisture causing slight degradation at the interface and the
adhesive bond to be affected. It is also important to note that even the brittle matrix is
relatively smooth with only a small amount of debonding. This is a characteristic of a
strongly bonded carbon fibre-epoxy resin laminate. The amount of failure at the interface
determines the overall fracture surface morphology.
Figure 5-12. Fracture surface of a dry [08]s specimen - magnification x10
Fibre Pull-out
Area of analysis
conducted by SEM
53
Figure 5-13. Fracture surface of a dry [08]s specimen - magnification x1000
Minor delamination of the top surface of the specimens occurred during the cutting of the
notches. This however is confined to the notch root vicinity and therefore was assumed to
have no effect on the ILSS results. This is evident in most of the lower magnification (x10)
figures but is clearly indicated in Figure 5-14.
Figure 5-14. Fracture surface of a wet [08]s specimen – 2month withdrawal - magnification x10
Delamination
54
Micro-cracking of the matrix is evident at the 2month withdrawal specimens (Figure 5-15).
The crack propagated along the fibre axis. In the wet specimens, the fracture surface is
characterized by the presence of numerous bare fibres. This is due to the moisture
penetration through the fibre/matrix interface causing debonding of the fibre and matrix,
exposing the fibres. However, areas of fibres still covered by matrix are still evident. This
indicates that some degree of adhesion was retained in wet state. The difference from a
brittle matrix and a ductile matrix is clearly evident (Figures 5-13 and 5-15).
Figure 5-15. Fracture surface of a wet [08]s specimen – 2month withdrawal – magnification x1000
It was not entirely clear if the micro-cracking occurred at the fibre/matrix interface or if it
occurred solely at the matrix. Huang and Sun (2006) effectively explained that the water
absorbed can cause swelling and plasticisation of the polymer matrix and debonding at the
fibre/matrix interface. However, this debonding was not evident at all specimens. This
draws the conclusion that water molecules may have come into free space or macro voids
in the laminate, formed by cavities and cracks that developed due to the residual stresses
after curing. This could have induced more cavities and cracks, subsequently leading to
micro cracking occurring along the fibre direction.
Previously, no major differences were evident between the dry and two month withdrawal
specimens at low magnifications (Figures 5-12 and 5-14). However, at the four month
withdrawal specimens, a noticeable line was evident. This could be due to the fact that
when the laminates were pulled, the mismatch of ply properties caused a higher
interlaminar shear stress to develop in the ply interface near the free edge. This is often
Bare Fibres
Micro-cracking
55
referred to as the ‗Boundary Layer Effect‘ or ‗free edge effect‘ (Hayashi, 1967). These
visible lines were evident at all [08]s specimens tested after 4months but were not present at
the [06 902]s specimens. This is due to the fact that the fracture surface plies were orientated
differently in the [06 902]s specimens. Therefore, by alternating the laminate stacking
sequence and the fibre orientation of the plies, both interlaminar shear and normal stresses
could be reduced at the free edges. The diffusion characteristics discussed in section 5.1
showed that at the four month withdrawal the specimens were not fully saturated with
water. Delasi and Whiteside (1978) explained that epoxy resins absorb moisture, apparently
by instantaneous surface absorption and subsequent diffusion through the interior. This
means that at the point of half saturation the core of the specimen is nearly dry (Selzer and
Friedrich, 1995). This could be a possible explanation for why the line was only evident at
the four month withdrawal specimens, as the line occurs at the mid plane of the specimen.
However, due to the lack of previous reported knowledge this is merely an assumption.
Figure 5-16. Fracture surface of a wet [08]s specimen – 4 month withdrawal - magnification x10
The area was closely examined during SEM (Figure 5-17); however no noticeable
difference of the matrix or fibres could be concluded. A ductile matrix is even more evident
in the 4 month withdrawal specimens and no micro-cracking was visible (Figure 5-17).
Visible line
56
Analysis of the [06 902]s specimens, showed a less severe change of the fracture surface
with an increase in moisture content. Similarly to the [08]s specimens, no change at lower
magnification (x10) were evident. Figure 5-18 presents a fracture surface of a dry [06 902]s
specimen.
Figure 5-18. Fracture surface of a dry [06 902]s specimen - magnification x10
Figure 5-17. Fracture surface of a wet [08]s specimen – 4 month withdrawal - magnification x1000
57
Some problems arose during the coating of the specimen. Smooth, even surfaces are easily
coated while rough, uneven surfaces caused reflection problems. This is particularly
evident in Figure 5-19.
Figure 5-19. Fracture surface of a dry [06 902]s specimen - magnification x1000
The distribution of the fibres was non-uniform in the [06 902]s laminates. Fibres range from
being closed packed to being more loosely packed with larger areas of resin between them.
This can be compared to a [06 902]s wet specimen micrograph taken after 2months
immersion (Figure 5-20 and 5-21). Both dry and wet specimens show hackling and many
bare fibres. Hackling is less at the wet specimens which draws the conclusion that shear
failure of the resin occurred and fracture close to the fibre matrix interface (Selzer and
Friedrich, 1998).
Reflections
58
Figure 5-20. Fracture surface of a wet [06 902]s specimen – 2month withdrawal - magnification x10
A softening of the resin was observed (Figure 5-21) this is due to the increase in moisture
content. The fibre ends are also ill defined.
Figure 5-21. Fracture surface of a [06 902]s specimen - 2month withdrawal - magnification x1000
Fibre end
59
A particular thing to note was that no micro-cracking occurred at the [06 902]s specimens.
This could be due to the fact that the micro-cracking in the [08]s specimens occurred along
the fibre axis and occurred in the vertical direction, in other words, along the thickness of
the specimen. In the [06 902]s specimens, some 0° fibres from the adjacent plies are evident
at the fracture surface (Figure 5-21 and 5-22). The 0° fibres would thus have inhibited
micro-cracking in the through-the-thickness direction.
No major differences were found between the two month and four month withdrawal SEM
micrographs. This was expected, as the difference in percentage moisture content was
minimal. The percentage increase in ILSS values from two months to four months
immersion was also small (Section 5.2). However, more bare fibres and hackling are visible
at the four month withdrawal specimens (Figure 5-23).
Cohesive failure was evident at all interfaces. The occurrence of either cohesive or adhesive
failure will depend on the relative strengths of the interface and the fibre or matrix.
Cohesive failure involves fracture of either the fibre or the matrix, where true adhesive
failure occurs by separation at the interface (Gersappe and Robbins, 1996). The specimens
Figure 5-22. Fracture surface of a wet [06 902]s specimen – 4 month withdrawal - magnification x10
60
therefore seem to have maintained structural integrity, and there was no evidence of
complete breakdown of the matrix away from the fibre.
Although not as evident in these micrographs, a large amount of debris can be seen in
micrographs at lower magnifications (x100), these are illustrated in Appendix F. The
delamination visible by using optical microscopy and SEM may not necessarily be due to
the diffusion of water through the matrix. Interlaminar separation or delamination present at
the fracture surface could be due to the fact that during the interlaminar shear test, one
laminate tends to slide one lamina over adjacent ones, subsequently causing interlaminar
separation or delamination (Daniel and Ishai, 1994). These interlaminar stresses are a
function of the laminate stacking sequence, and thus can be controlled by proper design of
the stacking sequence (Daniel and Ishai, 1994).
Figure 5-23. Fracture surface of a wet [06 902]s specimen - 4month withdrawal - magnification x1000
Chapter 6
Conclusions and Future
Research
61
6. CONCLUSIONS AND FUTURE RESEARCH
This chapter summarizes the essential results, conclusions and deductions obtained from
this thesis. It also proposes future research topics and possible techniques that could be
used.
6. 1 Conclusions
A study on the effect of moisture absorption on the mechanical behaviour and on the
fibre/matrix interface of HTA/6376 composite material was conducted. This was
effectively examined by the investigation of the absorption characteristics of carbon fibre
epoxy laminates, the measurement and analysis of the weight gain and hygrothermal
induced expansion.
The major conclusions can be summarized as follows:
1. During the initial stages of absorption, the specimens exhibited Fickian Diffusion
behaviour. The second stage, the deterioration and relaxation stage, was not
documented due to the limitation on the immersion time.
2. Due to the time constraint the diffusion coefficient of the laminates could not be
calculated.
3. The specimen lay-up sequence affected the overall moisture absorbed, with a higher
moisture content of 0.9% for [06 902]s specimens, in comparison to 0.78% for the
[08]s specimens.
4. Hygrothermal induced volumetric expansion of up to 10.2 % for [08]s specimens and
8.7% for [06 902]s specimens were found.
5. The interlaminar shear strength values showed an increase of 11.3% and 18.7% for
[08]s and [06 902]s specimens respectively, when compared to the dry specimens.
6. The predominant reason for the increase in ILSS is due to the increase in flexibility
of the epoxy resin due to the absorbed moisture. This lead to higher elongation
values consequently increasing the attainable load.
7. The increase in ILSS is a function of exposure time, with the four month immersed
specimens having increased by a substantial amount.
8. The overall behaviour of composite material exposed to a 100% relative humidity
environment depends on the amount of moisture content present in the material.
62
9. No difference between the dry, two month and four month withdrawal strain fields
of the specimens were evident. This was mainly due to the limitation of the DIC, as
it is unable to detect such small values of strain.
10. SEM images showed a change from a brittle to a ductile fracture mode due to an
increase in moisture content. All SEM images showed resin adhering to fibres,
which indicated that good fibre/matrix adhesion was retained even in a wet state.
63
6.2 Recommendations for Future Research
There is no known publication which discusses the influence of moisture on carbon fibre-
reinforced polymer composites, which is immersed in de-ionized water at room temperature
in a very detailed way. Therefore the data generated in this thesis could be used as a
guideline for the design of components from this material under the influence of moisture.
However, after reflecting on the research questions addressed, several interesting future
research topics were noted. The author has tried to qualitatively purpose possible research
areas and techniques which could be used.
6.2.1 Raman Spectroscopy
Investigate the possibility of using Raman Spectroscopy in order to predict and follow the
effect of moisture absorption (Cervenka et al., 1989). This technique allows for a more
detailed analysis of the interfacial region and thereby will provide a greater insight into the
long-term effects due to moisture absorption.
6.2.2 Thermoplastics versus Thermosets
According to previous researchers (Daniel and Ishai, 1994; Baker et al., 2004; Chen-Chi
and Shih-Wen, 1991) thermoplastic matrices are less susceptible to moisture effects than
thermosets. Thermoplastics are also more easily amenable to mass production and repair
and therefore may become more favourable to use than thermosets. It may prove to be
beneficial to exclusively assess the difference in the diffusion coefficients and degradation
of the mechanical properties of these polymers.
6.2.3 Relative Humidity Chamber
Investigate the possibility of testing in a chamber where the temperature and humidity are
controlled. This would involve purchasing expensive equipment perhaps exceeding the
budget of a final year project; however the use of this method would greatly increase the
accuracy of the results as almost no interference would occur with the environment.
A limitation of this thesis was the time constraint on the immersion period. Through
purchase of a relative humidity chamber, this limitation would be eliminated as the
temperature could be controlled. Baker et al. (2007) predicted that an increase of 10% in
64
temperature would cause the diffusion rate to double. Therefore the level of saturation
would be reached quicker and an accurate determination of the diffusion coefficient could
be attained.
6.2.4 Reversible/Irreversible Effects
Literature has reported a great deal on the reversibility of the effects of moisture absorption
on composite materials (Matthews and Rawlings, 1994; Khan et al., 2010). It has been
reported that at low temperature, high relative humidity, the decrease in mechanical
properties is reversible once the material has dried. However, at high temperature, high
relative humidity the influence of moisture absorption causes irreversible effects (Selzer
and Friedrich, 1998). Therefore, in order to accurately predict the performance of a
composite structure, the reversibility or irreversibility of the effects due to moisture should
be investigated.
6.2.5 Epoxy Resin Toughness
Following the findings of this thesis, a clear relationship is evident between the increase in
moisture absorption and the change in toughness of the epoxy resin. Consequently, by
investigating the possibility to determine the toughness of the epoxy resin with an increase
in moisture content, a greater understanding of the degradation mechanism of the laminates
could be achieved. This can be determined by a simple tensile test, as this would allow for a
documented change in tensile strength, elongation and hence the elastic modulus, with an
increase in moisture content (Perreux and Suri, 1997).
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Appendices
A1
Appendix A: Turnitin Originality Report
Turnitin Originality Report
Processed on 03-18-11 11:30 AM GMT ID: 176864416 Word Count: 16212
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< 1% match (publications) V. Alvarez. "Cyclic Water Absorption Behavior of Glass--Vinylester and Glass--Epoxy Composites", Journal of Composite Materials, 05/01/2007
29
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30
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31
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33
A4
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34
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35
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36
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37
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38
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39
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40
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41
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42
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43
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44
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45
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A5
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48
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55
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A6
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70
A7
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75
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76
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77
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78
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79
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82
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83
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A8
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84
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85
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88
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89
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90
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92
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96
A9
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99
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100
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101
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102
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103
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104
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106
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110
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111
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112
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114
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115
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116
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117
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118
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119
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120
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121
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A11
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122
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123
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124
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125
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126
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127
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128
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129
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130
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131
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132
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133
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A12
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134
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135
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136
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137
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138
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144
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145
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A13
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146
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147
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148
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149
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150
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151
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155
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156
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A14
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160
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161
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162
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163
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164
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165
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169
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177
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178
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paper text:
B1
Appendix B: Specimen Dimensions
This appendix contains the specimen configuration and dimensions details. The data was
used during the manufacturing of the specimens.
Number of plies: 16
Thickness: 2mm
Notch width: 2mm
Notch depth: 1mm
All dimensions on diagram in millimetres.
Specimen A: [06 902]s
179
85 5
Specimen B: [08]s
179
85 5
Figure B-1. Specimen A - Configuration and dimensions
Figure B-2. Specimen B - Configuration and dimensions
C1
Appendix C: Drawing of clamp
This appendix contains the drawing of the clamp adapted from ASTM Standard D3846-08.
All dimensions on drawing in millimetres (mm).
D1
Appendix D: Mass gain and change in dimensions of specimens
This appendix contains the data obtained by the weekly weigh in procedure outlined in
section 4.1.3.
Appendix D1. Dry specimen dimensions
Table D1. Dry specimen dimensions [08]s
[08]s Section thickness Width (mm) Width (mm) Thickness(mm) Weight (g)
Dry 1 12.52 4.94 2.00 7.4821
Dry 2 12.65 5.39 2.02 7.5627
Dry 3 12.65 5.21 2.00 7.4821
Dry 4 12.71 5.21 2.01 7.5393
Dry 5 12.67 5.00 2.01 7.8369
Dry 6 12.64 5.22 2.00 7.7696
Dry 7 12.52 5.14 2.00 7.4388
Table D2. Dry specimens dimensions [06 902]s
[06 902]s Section thickness Width (mm) Width (mm) Thickness(mm) Weight (g)
Dry 1 12.65 5.63 2.00 7.593
Dry 2 12.42 5.27 2.01 7.5929
Dry 3 12.67 5.00 2.00 7.6847
Dry 4 12.62 5.27 2.00 7.5375
Dry 5 12.50 5.14 2.00 7.4965
Dry 6 12.53 5.01 2.00 7.5304
Dry 7 12.58 5.00 2.00 7.4807
D2
Appendix D2. Immersed [08]s specimen dimensions Table D3. Before immersion dimensions [08]s
[08]s Before Immersion
Withdrawal I
Section thickness (mm)
Width (mm)
Thickness (mm)
Weight (g)
Volume (mm3)
I-1 12.33 5.17 2.00 7.3817 127.4922
I-2 12.67 5.36 2.00 7.5258 135.8224
I-3 12.68 5.17 2.00 7.5321 131.1112
I-4 12.49 5.50 2.01 7.3638 138.0769
I-5 12.63 5.08 2.00 7.5499 128.3208
I-6 12.64 5.26 2.00 7.5384 132.9728
I-7 12.63 5.21 2.01 7.8069 132.2626
Withdrawal II
Section thickness (mm)
Width (mm)
Thickness (mm)
Weight (g)
Volume (mm3)
II-1 12.32 5.15 2.00 7.4158 126.89600
II-2 12.63 4.93 2.02 7.5998 125.77711
II-3 12.74 5.23 2.00 7.5940 133.26040
II-4 12.59 5.48 2.00 7.5252 138.13748
II-5 12.67 5.53 2.01 7.7774 140.83085
II-6 12.71 5.28 1.99 7.5268 133.54651
II-7 12.55 5.54 2.00 7.4723 139.05400
Room Temperature: 19°C
Water Temperature: 19°C
Notes: -------
D3
Table D4. Specimen Dimensions [08]s – Week 1
[08]s Week 1
Withdrawal I
Section thickness (mm)
Width (mm)
Thickness (mm)
Weight (g)
% Weight gain
Volume (mm3) % ∆V
I-1 12.40 5.12 2.07 7.3968 0.2045 131.42 3.0809
I-2 12.59 5.39 2.06 7.5424 0.2205 139.79 2.9224
I-3 12.78 5.37 2.06 7.5476 0.2057 141.37 7.8282
I-4 12.59 5.44 2.08 7.3802 0.2227 142.66 3.3248
I-5 12.75 4.93 2.06 7.5675 0.2331 129.48 0.9083
I-6 12.64 5.30 2.07 7.5548 0.2175 138.67 4.2870
I-7 12.88 5.20 2.05 7.8245 0.2254 137.30 3.8092
Withdrawal II
Section thickness (mm)
Width (mm)
Thickness (mm)
Weight (g)
% Weight gain
Volume (mm3) % ∆V
II-1 12.36 5.19 2.07 7.4309 0.2036 132.78 4.6425
II-2 12.85 5.09 2.06 7.6153 0.2039 134.73 7.1239
II-3 12.74 5.24 2.07 7.6110 0.2238 138.18 3.6978
II-4 12.80 5.31 2.08 7.5431 0.2378 141.37 2.3425
II-5 12.60 5.33 2.05 7.7933 0.2044 137.67 2.2416
II-6 12.56 5.57 2.04 7.5412 0.1913 142.71 6.8667
II-7 12.58 5.56 2.06 7.4896 0.2315 144.08 3.6189
Room Temperature: 19°C
Water Temperature: 19°C
Notes: --------
D4
Table D5. Specimen Dimensions [08]s – Week 2
Room Temperature: 19°C
Water Temperature: 18°C
Notes: -------
[08]s Week 2
Withdrawal I
Section thickness (mm)
Width (mm)
Thickness (mm)
Weight (g)
% Weight gain
Volume (mm3) % ∆V
I-1 12.40 5.14 2.07 7.4020 0.2750 135.40 6.2069
I-2 12.59 5.44 2.12 7.5460 0.2684 146.21 7.6541
I-3 12.78 5.31 2.12 7.5520 0.2642 142.49 8.6841
I-4 12.59 5.50 2.10 7.3860 0.3014 144.34 4.5437
I-5 12.75 5.08 2.08 7.5710 0.2794 136.12 6.0830
I-6 12.64 5.31 2.07 7.5590 0.2732 140.83 5.9067
I-7 12.88 5.12 2.06 7.8300 0.2950 146.37 10.670
Withdrawal II
Section thickness (mm)
Width (mm)
Thickness (mm)
Weight (g)
% Weight gain
Volume (mm3) % ∆V
II-1 12.40 5.37 2.14 7.4360 0.2723 142.47 10.295
II-2 12.85 5.09 2.13 7.6200 0.2657 134.90 7.1239
II-3 12.80 5.29 2.17 7.6160 0.2899 146.93 10.261
II-4 12.67 5.31 2.16 7.5480 0.3029 143.41 10.281
II-5 12.63 5.33 2.16 7.7980 0.2648 161.22 14.486
II-6 12.56 5.57 2.14 7.5460 0.2550 149.39 11.868
II-7 12.58 5.56 2.21 7.4940 0.2904 154.02 10.764
D5
Table D6. Specimen Dimensions [08]s – Week 3
Room Temperature: 19°C
Water Temperature: 18°C
Notes: -------
[08]s Week 3
Withdrawal I
Section thickness (mm)
Width (mm)
Thickness (mm)
Weight (g)
% Weight gain
Volume (mm3) % ∆V
I-1 12.40 5.14 2.07 7.4073 0.3468 135.50 6.3109
I-2 12.59 5.44 2.12 7.5525 0.3547 146.21 5.6110
I-3 12.78 5.31 2.12 7.5600 0.3704 142.49 7.5194
I-4 12.59 5.50 2.10 7.3898 0.3530 144.34 4.5612
I-5 12.75 5.08 2.08 7.5759 0.3443 138.51 6.0830
I-6 12.64 5.31 2.09 7.5645 0.3462 140.90 5.9067
I-7 12.88 5.12 2.25 7.8352 0.3624 146.37 10.670
Withdrawal II
Section thickness (mm)
Width (mm)
Thickness (mm)
Weight (g)
% Weight gain
Volume (mm3) % ∆V
II-1 12.40 5.37 2.18 7.4421 0.3546 142.47 10.295
II-2 12.85 5.09 2.15 7.6260 0.3447 134.90 7.1239
II-3 12.80 5.29 2.15 7.6201 0.2899 146.93 10.261
II-4 12.67 5.31 2.17 7.5529 0.3029 143.41 10.281
II-5 12.63 5.33 2.18 7.8034 0.2648 161.22 14.486
II-6 12.56 5.57 2.09 7.5496 0.2550 149.39 11.868
II-7 12.58 5.56 2.23 7.4974 0.2904 154.02 10.764
D6
Table D7. Specimen Dimensions [08]s – Week 4
Room Temperature: 19°C
Water Temperature: 17°C
Notes: -------
[08]s Week 4
Withdrawal I
Section thickness (mm)
Width (mm)
Thickness (mm)
Weight (g)
% Weight gain
Volume (mm3) % ∆V
I-1 12.41 5.04 2.1 7.4094 0.375252 131.3474 3.023903
I-2 12.49 5.42 2.17 7.5562 0.403944 146.8999 8.155861
I-3 12.67 5.34 2.15 7.5622 0.399623 145.4643 10.94725
I-4 12.55 5.49 2.13 7.395 0.423694 146.7559 6.285615
I-5 12.85 5.05 2.11 7.5801 0.400005 136.9881 6.754375
I-6 12.86 5.36 2.15 7.5722 0.448371 148.1986 11.45034
I-7 12.80 5.17 2.29 7.837 0.385556 151.543 14.57737
Withdrawal II
Section thickness (mm)
Width (mm)
Thickness (mm)
Weight (g)
% Weight gain
Volume (mm3) % ∆V
II-1 12.64 5.17 2.14 7.4474 0.426117 139.8464 10.20555
II-2 12.88 5.05 2.12 7.6325 0.430274 137.8933 9.633042
II-3 12.90 5.23 2.15 7.6283 0.451672 145.0541 8.850078
II-4 12.84 5.24 2.08 7.5592 0.451815 139.9457 1.309021
II-5 12.85 5.37 2.05 7.8091 0.407591 141.4592 0.446191
II-6 12.73 5.44 2.18 7.5555 0.381304 150.9676 13.04497
II-7 12.72 5.54 2.18 7.5044 0.429587 153.622 10.47649
D7
Table D8. Specimen Dimensions [08]s – Week 5
Room Temperature: 19°C
Water Temperature: 19°C
Notes: -------
[08]s Week 5
Withdrawal I
Section thickness (mm)
Width (mm)
Thickness (mm)
Weight (g)
% Weight gain
Volume (mm3) % ∆V
I-1 12.44 5.04 2.10 7.4138 0.434859 131.665 3.272953
I-2 12.65 5.34 2.12 7.5638 0.50493 143.2081 5.437778
I-3 12.69 5.38 2.10 7.5626 0.404934 143.3716 9.351161
I-4 12.57 5.54 2.12 7.3989 0.476656 147.6321 6.920189
I-5 12.87 5.07 2.12 7.5826 0.433118 138.3319 7.801625
I-6 12.86 5.36 2.16 7.5723 0.449698 148.8879 11.96872
I-7 12.84 5.17 2.13 7.8424 0.454726 141.3954 6.905005
Withdrawal II
Section thickness (mm)
Width (mm)
Thickness (mm)
Weight (g)
% Weight gain
Volume (mm3) % ∆V
II-1 12.64 5.09 2.17 7.4476 0.428814 139.6126 10.02127
II-2 12.92 5.05 2.12 7.6348 0.460538 138.3215 9.973517
II-3 12.96 5.22 2.14 7.6275 0.441138 144.7736 8.639602
II-4 12.84 5.28 2.12 7.5575 0.429224 143.7258 4.045494
II-5 12.81 5.59 2.10 7.8098 0.416592 150.3766 6.778159
II-6 12.71 5.44 2.18 7.556 0.387947 150.7304 12.86737
II-7 12.72 5.54 2.20 7.5047 0.433601 155.0314 11.49004
D8
Table D9. Specimen Dimensions [08]s – Week 6
Room Temperature: 19°C
Water Temperature: 19°C
Notes: -------
[08]s Week 6
Withdrawal I
Section thickness (mm)
Width (mm)
Thickness (mm)
Weight (g)
% Weight gain
Volume (mm3) % ∆V
I-1 12.47 5.03 2.11 7.4152 0.453825 132.3479 3.808587
I-2 12.66 5.31 2.15 7.5601 0.455766 144.5329 6.413147
I-3 12.70 5.37 2.14 7.5661 0.451401 145.9459 11.31456
I-4 12.61 5.52 2.12 7.3989 0.476656 147.5673 6.873207
I-5 12.86 5.09 2.11 7.5854 0.470205 138.1151 7.632678
I-6 12.83 5.29 2.14 7.5753 0.489494 145.2433 9.227826
I-7 12.90 5.19 2.23 7.8452 0.490592 149.3007 12.88203
Withdrawal II
Section thickness (mm)
Width (mm)
Thickness (mm)
Weight (g)
% Weight gain
Volume (mm3) % ∆V
II-1 12.58 5.12 2.13 7.4511 0.476011 137.1924 8.114084
II-2 12.92 5.01 2.12 7.6343 0.453959 137.2259 9.102439
II-3 12.93 5.23 2.13 7.631 0.487227 144.0389 8.088305
II-4 12.91 5.23 2.11 7.5624 0.494339 142.4657 3.133286
II-5 12.84 5.62 2.12 7.8186 0.52974 152.9809 8.627403
II-6 12.77 5.45 2.18 7.5588 0.425147 151.7204 13.60864
II-7 12.73 5.56 2.16 7.5084 0.483118 152.8822 9.944488
D9
Table D10. Specimen Dimensions [08]s – Week 7
Room Temperature: 19°C
Water Temperature: 19°C
Notes: -------
[08]s Week 7
Withdrawal I
Section thickness (mm)
Width (mm)
Thickness (mm)
Weight (g)
% Weight gain
Volume (mm3) % ∆V
I-1 12.55 5.13 2.15 7.4237 0.568975 138.4202 8.571524
I-2 12.77 5.43 2.10 7.5723 0.617875 145.6163 7.210821
I-3 12.78 5.36 2.12 7.5738 0.55363 145.2217 10.76224
I-4 12.55 5.49 2.11 7.4086 0.608382 145.3779 5.287628
I-5 12.88 5.02 2.12 7.5978 0.634445 137.0741 6.821429
I-6 12.81 5.31 2.12 7.5831 0.592964 144.2047 8.446789
I-7 12.85 5.13 2.11 7.8555 0.622526 139.0923 5.16369
Withdrawal II
Section thickness (mm)
Width (mm)
Thickness (mm)
Weight (g)
% Weight gain
Volume (mm3) % ∆V
II-1 12.62 5.1 2.07 7.4636 0.64457 133.2293 4.990969
II-2 12.90 5.03 2.10 7.6389 0.514487 136.2627 8.336637
II-3 12.94 5.19 2.11 7.6388 0.589939 141.7046 6.336651
II-4 12.88 5.21 2.07 7.5676 0.56344 138.9069 0.557022
II-5 12.84 5.57 2.10 7.8227 0.582457 150.1895 6.645297
II-6 12.75 5.47 2.11 7.569 0.560663 147.1567 10.19133
II-7 12.72 5.56 2.19 7.5149 0.570106 154.8838 11.38393
D10
Table D11. Specimen Dimensions [08]s – Week 8
Room Temperature: 17°C
Water Temperature: 16°C
Notes:
Week 9 – Unable to take moisture gain and specimen dimensions due to Christmas
holidays.
[08]s Week 8
Withdrawal I
Section thickness (mm)
Width (mm)
Thickness (mm)
Weight (g)
% Weight gain
Volume (mm3) % ∆V
I-1 12.57 5.13 2.15 7.4267 0.609616 138.6408 8.744547
I-2 12.77 5.43 2.15 7.5743 0.64445 149.0834 9.763459
I-3 12.81 5.37 2.14 7.5768 0.59346 147.21 12.27871
I-4 12.56 5.51 2.11 7.4124 0.659985 146.0238 5.755389
I-5 12.88 5.05 2.14 7.5988 0.647691 139.1942 8.473576
I-6 12.83 5.31 2.13 7.5841 0.606229 145.1111 9.128445
I-7 12.87 5.18 2.12 7.8555 0.622526 141.3332 6.857999
Withdrawal II
Section thickness (mm)
Width (mm)
Thickness (mm)
Weight (g)
% Weight gain
Volume (mm3) % ∆V
II-1 12.62 5.10 2.09 7.4572 0.558267 134.5166 6.005374
II-2 12.90 5.03 2.12 7.6417 0.55133 137.5604 9.368415
II-3 12.92 5.22 2.14 7.6374 0.571504 144.3267 8.304294
II-4 12.88 5.27 2.10 7.5688 0.579387 142.543 3.189200
II-5 12.82 5.56 2.10 7.8181 0.523311 149.6863 6.288018
II-6 12.79 5.57 2.11 7.5701 0.575278 150.317 12.55781
II-7 12.71 5.56 2.20 7.5151 0.572782 155.4687 11.80457
D11
Table D12. Specimen Dimensions [08]s – Week 10
[08]s Week 10
Withdrawal II
Section thickness (mm)
Width (mm)
Thickness (mm)
Weight (g)
% Weight gain
Volume (mm3) % ∆V
II-1 12.59 5.14 2.13 7.4625 0.629737 137.8378 8.622682
II-2 12.91 5.01 2.13 7.6535 0.706598 137.7665 9.532231
II-3 12.98 5.22 2.14 7.6452 0.674216 144.997 8.807256
II-4 12.88 5.27 2.11 7.5772 0.691012 143.2217 3.680577
II-5 12.83 5.61 2.10 7.8236 0.594029 151.1502 7.327499
II-6 12.76 5.47 2.13 7.5710 0.587235 148.6680 11.32304
II-7 12.71 5.56 2.20 7.5181 0.61293 155.4687 11.80457
Room Temperature: 18°C
Water Temperature: 16°C
Notes: -------
Table D13. Specimen Dimensions [08]s – Week 11
[08]s Week 11
Withdrawal II
Section thickness (mm)
Width (mm)
Thickness (mm)
Weight (g)
% Weight gain
Volume (mm3) % ∆V
II-1 12.52 5.14 2.14 7.4656 0.671539 137.715 8.525873
II-2 12.95 5.04 2.09 7.6593 0.782915 136.4101 8.453845
II-3 12.96 5.22 2.15 7.6477 0.707137 145.4501 9.147264
II-4 12.88 5.27 2.11 7.5772 0.691012 143.2217 3.680577
II-5 12.85 5.61 2.13 7.8237 0.595315 153.5485 9.030446
II-6 12.77 5.47 2.15 7.5727 0.609821 150.1816 12.45639
II-7 12.71 5.57 2.20 7.5199 0.637019 155.7483 12.00565
Room Temperature: 19°C
Water Temperature: 18°C
Notes: -------
D12
Table D14. Specimen Dimensions [08]s – Week 12
[08]s Week 12
Withdrawal II
Section thickness (mm)
Width (mm)
Thickness (mm)
Weight (g)
% Weight gain
Volume (mm3) % ∆V
II-1 12.55 5.14 2.14 7.4656 0.671539 138.045 8.785919
II-2 12.95 5.04 2.13 7.6593 0.782915 139.0208 10.52952
II-3 12.96 5.22 2.15 7.6485 0.717672 145.4501 9.147264
II-4 12.88 5.27 2.11 7.5772 0.691012 143.2217 3.680577
II-5 12.89 5.61 2.13 7.8255 0.618459 154.0265 9.36984
II-6 12.77 5.47 2.15 7.5738 0.624435 150.1816 12.45639
II-7 12.71 5.57 2.2 7.5219 0.663785 155.7483 12.00565
Room Temperature: 19°C
Water Temperature: 17°C
Notes: -------
Table D15. Specimen Dimensions [08]s – Week 13
[08]s Week 13
Withdrawal II
Section thickness (mm)
Width (mm)
Thickness (mm)
Weight (g)
% Weight gain
Volume (mm3) % ∆V
II-1 12.57 5.14 2.14 7.4710 0.744357 138.265 8.959283
II-2 12.95 5.04 2.10 7.6593 0.782915 137.0628 8.972762
II-3 12.99 5.23 2.15 7.6506 0.745325 146.0661 9.609498
II-4 12.88 5.28 2.12 7.6000 0.993994 144.1736 4.369624
II-5 12.89 5.61 2.14 7.8286 0.658318 154.7496 9.883314
II-6 12.78 5.47 2.16 7.5765 0.660307 150.9983 13.06791
II-7 12.71 5.57 2.19 7.5240 0.691889 155.0404 11.49654
Room Temperature: 14°C
Water Temperature: 11°C
Notes: Decrease in the rate of percentage moisture gain, could be due to the severe drop in
temperature. Room temperature 1°C drop when compared to standard room temperature.
Water temperature 3°C colder than usual.
D13
Room Temperature: 15°C
Water Temperature: 11°C
Notes: Severe drop in temperature from original immersion temperature.
Table D 17. Specimen Dimensions [08]s - Week 15
[08]s Week 15
Withdrawal II
Section thickness (mm)
Width (mm)
Thickness (mm)
Weight (g)
% Weight gain
Volume (mm3) % ∆V
II-1 12.61 5.10 2.16 7.4725 0.764584 138.9118 9.468982
II-2 12.97 4.99 2.11 7.6547 0.722387 136.5598 8.572875
II-3 12.99 5.26 2.16 7.6534 0.782196 147.5872 10.75097
II-4 12.96 5.28 2.15 7.5824 0.760113 147.1219 6.503984
II-5 12.91 5.57 2.12 7.833 0.714892 152.4464 8.247904
II-6 12.79 5.48 2.16 7.5788 0.690865 151.3927 13.36325
II-7 12.77 5.55 2.24 7.5271 0.733375 158.7566 14.16906
Room Temperature: 19°C
Water Temperature: 17°C
Notes:
[08]s Week 14
Withdrawal II
Section thickness (mm)
Width (mm)
Thickness (mm)
Weight (g)
% Weight gain
Volume (mm3) % ∆V
II-1 12.61 5.12 2.14 7.4717 0.753796 138.1652 8.880696
II-2 12.96 5.04 2.13 7.6525 0.693439 139.1282 10.61487
II-3 12.99 5.23 2.16 7.651 0.750593 146.7454 10.11931
II-4 12.93 5.28 2.09 7.5812 0.744166 142.6851 3.292123
II-5 12.92 5.61 2.12 7.833 0.714892 153.6601 9.109718
II-6 12.78 5.47 2.12 7.5769 0.665622 148.202 10.97406
II-7 12.75 5.55 2.19 7.525 0.705271 154.9699 11.44582
Table D 16. Specimen Dimensions [08]s - Week 14
D14
Table D18. Specimen Dimensions [08]s - Week 16
[08]s Week 16
Withdrawal II
Section thickness (mm)
Width (mm)
Thickness (mm)
Weight (g)
% Weight gain
Volume (mm3) % ∆V
II-1 12.59 5.13 2.17 7.475 0.798296 140.1531 10.44725
II-2 12.97 5.04 2.13 7.656 0.739493 139.2355 10.70022
II-3 12.99 5.23 2.17 7.651 0.750593 147.4248 10.62912
II-4 12.93 5.26 2.15 7.60 0.993994 146.2254 5.854957
II-5 12.92 5.61 2.12 7.8338 0.725178 153.6601 9.109718
II-6 12.78 5.47 2.14 7.5808 0.717436 149.6001 12.02099
II-7 12.78 5.58 2.21 7.5294 0.764156 157.6004 13.33756
Room Temperature: 19°C
Water Temperature: 18°C
Notes:
D15
Appendix D3. Immersed [06 902]s specimen dimensions
Table D19. Specimen Dimensions [06 902]s - Before immersion
[06 902]s Before Immersion
Withdrawal 1
Section thickness (mm)
Width (mm)
Thickness (mm)
Weight (g)
Volume (mm3)
I-1 12.69 5.33 2.00 7.6918 135.2754
I-2 12.39 5.06 2.01 7.387 126.01373
I-3 12.71 5.03 2.02 7.581 129.14123
I-4 12.54 5.0 2.00 7.5139 125.4000
I-5 12.44 5.0 2.01 7.412 125.022
I-6 12.57 5.18 2.00 7.5261 130.2252
I-7 12.56 5.14 2.02 7.4927 130.40797
Withdrawal 2
Section thickness (mm)
Width (mm)
Thickness (mm)
Weight (g)
Volume (mm3)
II-1 12.58 5.00 2.00 7.5822 125.8000
II-2 12.71 4.99 2.00 7.591 126.8458
II-3 12.57 5.00 2.00 7.5178 125.7000
II-4 12.61 5.02 2.02 7.5143 127.87044
II-5 12.66 4.95 2.00 7.603 125.3340
II-6 12.58 5.12 2.01 7.4864 129.4633
II-7 12.52 5.07 2.00 7.5324 126.9528
Room Temperature: 19°C
Water Temperature: 19°C
Notes: -------
D16
Table D20. Specimen Dimensions [06 902]s – Week 1
[06 902]s Week 1
Withdrawal 1
Section thickness (mm)
Width (mm)
Thickness (mm)
Weight (g)
% Weight gain
Volume (mm3) % ∆V
I-1 12.69 5.27 2.10 7.710 0.23661561 140.44023 3.81801125
I-2 12.47 5.04 2.12 7.406 0.25720861 133.239456 5.73407498
I-3 12.71 5.06 2.13 7.601 0.26381743 137.072060 6.14121039
I-4 12.63 5.07 2.06 7.558 0.58691225 131.910246 5.19158373
I-5 12.49 5.06 2.08 7.433 0.28332433 131.454752 5.14529602
I-6 12.58 5.28 2.07 7.545 0.25112601 137.494368 5.58199795
I-7 12.58 5.18 2.05 7.512 0.25758404 133.58702 2.43777435
Withdrawal 2
Section thickness (mm)
Width (mm)
Thickness (mm)
Weight (g)
% Weight gain
Volume (mm3) % ∆V
II-1 12.64 4.96 2.11 7.602 0.26113792 132.285184 5.15515421
II-2 12.72 5.03 2.00 7.612 0.27664339 127.96320 0.8809121
II-3 12.61 4.94 2.10 7.536 0.2420921 130.81614 4.07011933
II-4 12.57 5.08 2.08 7.533 0.2488588 132.819648 3.87048315
II-5 12.68 4.96 2.06 7.622 0.2499013 129.559168 3.37112674
II-6 12.61 5.1 2.05 7.506 0.2618080 131.83755 1.83392055
II-7 12.51 5.26 2.01 7.555 0.3040199 132.263226 4.18299241
Room Temperature: 19°C
Water Temperature: 19°C
Notes: -------
D17
Table D21. Specimen Dimensions [06 902]s – Week 2
[06 902]s Week 2
Withdrawal 1
Section thickness (mm)
Width (mm)
Thickness (mm)
Weight (g)
% Weight gain
Volume (mm3) % ∆V
I-1 12.68 5.26 2.23 7.716 0.314620765 148.733864 9.94893676
I-2 12.35 5.03 2.20 7.412 0.338432381 136.66510 8.45254375
I-3 12.67 4.94 2.22 7.608 0.356153542 138.949356 7.59488685
I-4 12.68 5.04 2.16 7.567 0.706690267 138.039552 10.0793875
I-5 12.59 5.01 2.17 7.44 0.377765785 136.874703 9.48049383
I-6 12.58 5.21 2.17 7.551 0.330848647 142.225706 9.21519490
I-7 12.65 5.15 2.18 7.519 0.351008315 142.02155 8.90557699
Withdrawal 2
Section thickness (mm)
Width (mm)
Thickness (mm)
Weight (g)
% Weight gain
Volume (mm3) % ∆V
II-1 12.63 4.96 2.21 7.608 0.340270634 138.445008 10.0516756
II-2 12.68 4.52 1.90 7.619 0.368857858 108.89584 14.1510085
II-3 12.60 5.02 2.21 7.551 0.441618559 139.78692 11.2067780
II-4 12.60 5.00 2.20 7.54 0.342014559 138.60000 8.39095858
II-5 12.66 5.00 2.19 7.629 0.341970275 138.62700 10.6060606
II-6 12.67 5.07 2.18 7.513 0.355310964 140.036442 8.1669062
II-7 12.51 5.07 2.22 7.559 0.353141097 140.805054 10.9113418
Room Temperature: 19°C
Water Temperature: 19°C
Notes: -------
D18
Table D22. Specimen Dimensions [06 902]s – Week 3
[06 902]s Week 3
Withdrawal 1
Section thickness (mm)
Width (mm)
Thickness (mm)
Weight (g)
% Weight gain
Volume (mm3) % ∆V
I-1 12.62 5.26 2.19 7.7250 0.44943820 145.374828 7.4658274
I-2 12.31 5.05 2.09 7.4174 0.40100250 129.925895 3.10455128
I-3 12.66 5.13 2.04 7.6134 0.43120084 132.489432 2.59267013
I-4 12.55 4.96 2.12 7.5708 0.76767404 131.965760 5.2358532
I-5 12.42 5 2.14 7.4440 0.42518701 132.894000 6.29649181
I-6 12.53 5 2.10 7.5571 0.41373603 131.565000 1.02883312
I-7 12.58 5.1 2.14 7.524 0.41773993 137.298120 5.28353604
Withdrawal 2
Section thickness (mm)
Width (mm)
Thickness (mm)
Weight (g)
% Weight gain
Volume (mm3) % ∆V
II-1 12.47 5.03 2.05 7.6416 0.78250559 128.646274 2.26253895
II-2 12.64 4.96 2.17 7.6234 0.43097714 136.046848 7.25372696
II-3 12.56 5.04 2.18 7.5480 0.40190037 137.999232 9.78459188
II-4 12.50 5.01 2.11 7.5447 0.39984216 132.201375 3.38696798
II-5 12.65 4.93 2.13 7.6354 0.43278478 132.836385 5.98591363
II-6 12.53 5.19 2.14 7.5186 0.42748659 139.6859436 7.89617437
II-7 12.40 5.02 2.13 7.5654 0.43810737 132.588240 4.43900410
Room Temperature: 19°C
Water Temperature: 18°C
Notes: -------
D19
Table D23. Specimen Dimensions [06 902]s - Week 4
[06 902]s Week 4
Withdrawal 1
Section thickness (mm)
Width (mm)
Thickness (mm)
Weight (g)
% Weight gain
Volume (mm3) % ∆V
I-1 12.78 5.07 2.14 7.7327 0.51223 138.660 2.502335236
I-2 12.84 4.92 2.18 7.4220 0.47380 137.716 9.287059139
I-3 12.92 5.01 2.16 7.6194 0.50652 139.815 8.265250633
I-4 12.78 4.98 2.10 7.5787 0.86240 133.653 6.581531100
I-5 12.60 4.98 2.08 7.4523 0.54371 130.515 4.394298603
I-6 12.78 5.10 2.10 7.5652 0.51952 136.873 5.105463459
I-7 12.87 5.07 2.15 7.5299 0.49648 140.289 7.577349108
Withdrawal 2
Section thickness (mm)
Width (mm)
Thickness (mm)
Weight (g)
% Weight gain
Volume (mm3) % ∆V
II-1 12.79 4.91 2.13 7.6192 0.48798 133.761 6.328821145
II-2 12.88 4.94 2.09 7.6277 0.48346 132.980 4.83661895
II-3 12.76 4.97 2.10 7.5486 0.40969 133.176 5.947589499
II-4 12.70 5.01 2.13 7.5547 0.53764 135.525 5.986579667
II-5 12.91 4.95 2.12 7.6442 0.54189 135.477 8.093206951
II-6 12.78 5.01 2.12 7.5254 0.52094 135.738 4.847427954
II-7 12.68 5.01 2.10 7.5731 0.54033 133.406 5.083369567
Room Temperature: 19°C
Water Temperature: 17°C
Notes: -------
D20
Table D24. Specimen Dimensions [06 902]s - Week 5
[06 902]s Week 5
Withdrawal 1
Section thickness (mm)
Width (mm)
Thickness (mm)
Weight (g)
% Weight gain
Volume (mm3) % ∆V
I-1 12.92 5.17 2.12 7.7312 0.512234 141.6084 4.681537
I-2 12.86 4.92 2.19 7.7712 5.201029 138.5639 9.959386
I-3 12.92 4.95 2.12 7.6206 0.522359 135.5825 4.98776
I-4 12.79 4.98 2.13 7.5795 0.873049 135.6686 8.188713
I-5 12.61 4.94 2.09 7.4523 0.543713 130.1932 4.136237
I-6 12.8 5.11 2.08 7.5648 0.514211 136.0486 4.471823
I-7 12.77 5.07 2.15 7.5324 0.529849 139.1994 6.741472
Withdrawal 2
Section thickness (mm)
Width (mm)
Thickness (mm)
Weight (g)
% Weight gain
Volume (mm3) % ∆V
II-1 12.71 4.91 2.13 7.6218 0.522276 132.925 5.663746
II-2 12.89 4.94 2.11 7.6324 0.545383 134.3576 5.922014
II-3 12.75 5.01 2.09 7.5579 0.533401 133.504 6.208413
II-4 12.72 5.01 2.08 7.5553 0.545626 132.5526 3.661622
II-5 12.89 4.96 2.10 7.6443 0.543207 134.2622 7.123558
II-6 12.78 4.96 2.10 7.5264 0.534302 133.1165 2.821791
II-7 12.70 5.02 2.14 7.5751 0.566884 136.4336 7.467941
Room Temperature: 19°C
Water Temperature: 19°C
Notes: -------
D21
Table D25. Specimen Dimensions [06 902]s - Week 6
[06 902]s Week 6
Withdrawal 1
Section thickness (mm)
Width (mm)
Thickness (mm)
Weight (g)
% Weight gain
Volume (mm3) % ∆V
I-1 12.84 5.17 2.17 7.7373 0.591539 144.0507 6.486971
I-2 12.86 4.92 2.13 7.7764 5.271423 134.7677 6.9468
I-3 12.78 4.95 2.17 7.6274 0.612056 137.2764 6.299417
I-4 12.82 4.98 2.05 7.5889 0.99815 130.8794 4.369522
I-5 12.62 4.94 2.12 7.4564 0.599029 132.1667 5.714783
I-6 12.72 5.15 2.08 7.5689 0.568688 136.2566 4.631546
I-7 12.74 5.09 2.14 7.5369 0.589908 138.7717 6.413531
Withdrawal 2
Section thickness (mm)
Width (mm)
Thickness (mm)
Weight (g)
% Weight gain
Volume (mm3) % ∆V
II-1 12.73 4.91 2.12 7.6266 0.585582 132.5091 5.333161
II-2 12.93 4.93 2.12 7.6367 0.602029 135.1392 6.538165
II-3 12.76 5.03 2.10 7.5613 0.578627 134.7839 7.226635
II-4 12.68 4.95 2.11 7.5585 0.588212 132.4363 3.570658
II-5 12.90 4.96 2.12 7.6467 0.574773 135.6461 8.22768
II-6 12.78 4.98 2.11 7.5298 0.579718 134.2897 3.727997
II-7 12.66 5.03 2.12 7.5796 0.626626 135.0012 6.33966
Room Temperature: 19°C
Water Temperature: 19°C
Notes: -------
D22
Table D26. Specimen Dimensions [06 902]s - Week 7
[06 902]s Week 7
Withdrawal 1
Section thickness (mm)
Width (mm)
Thickness (mm)
Weight (g)
% Weight gain
Volume (mm3) % ∆V
I-1 12.90 5.20 2.17 7.7427 0.661744 145.5636 7.605374
I-2 12.87 4.93 2.17 7.7828 5.358061 137.6845 9.26154
I-3 12.93 4.98 2.11 7.6320 0.672734 135.8659 5.207189
I-4 12.81 5.02 2.07 7.5897 1.008797 133.1138 6.151383
I-5 12.64 4.97 2.10 7.4637 0.697518 131.9237 5.520372
I-6 12.78 5.13 2.10 7.5748 0.647081 137.6789 5.723731
I-7 12.75 5.09 2.10 7.5421 0.659308 136.2848 4.506459
Withdrawal 2
Section thickness (mm)
Width (mm)
Thickness (mm)
Weight (g)
% Weight gain
Volume (mm3) % ∆V
II-1 12.77 4.91 2.15 7.6351 0.697687 134.8065 7.159384
II-2 12.89 4.91 2.11 7.6434 0.690291 133.5417 5.278763
II-3 12.74 5.08 2.11 7.568 0.667749 136.5575 8.637639
II-4 12.75 4.97 2.09 7.5658 0.68536 132.4381 3.572077
II-5 12.81 4.97 2.13 7.6528 0.655005 135.6079 8.19725
II-6 12.79 4.99 2.12 7.5365 0.669214 135.3029 4.510588
II-7 12.71 5.02 2.09 7.5821 0.659816 133.3508 5.039651
Room Temperature: 19°C
Water Temperature: 19°C
Notes: -------
D23
Table D27. Specimen Dimensions [06 902]s - Week 8
[06 902]s Week 8
Withdrawal 1
Section thickness (mm)
Width (mm)
Thickness (mm)
Weight (g)
% Weight gain
Volume (mm3) % ∆V
I-1 12.95 5.2 2.17 7.7457 0.700746 146.1278 8.022449
I-2 12.91 4.93 2.17 7.7843 5.378367 138.1125 9.601126
I-3 12.93 4.98 2.11 7.6358 0.72286 135.8659 5.207189
I-4 12.83 5.02 2.06 7.5932 1.055377 132.6776 5.803506
I-5 12.67 4.99 2.12 7.4645 0.708311 134.0334 7.207848
I-6 12.80 5.13 2.14 7.5761 0.664355 140.521 7.90612
I-7 12.76 5.1 2.13 7.5467 0.720701 138.6119 6.290959
Withdrawal 2
Section thickness (mm)
Width (mm)
Thickness (mm)
Weight (g)
% Weight gain
Volume (mm3) % ∆V
II-1 12.81 4.9 2.13 7.6351 0.697687 133.698 6.278196
II-2 12.94 4.95 2.11 7.6462 0.727177 135.1518 6.548132
II-3 12.77 5.06 2.11 7.5687 0.67706 136.3402 8.464743
II-4 12.76 4.97 2.09 7.5684 0.719961 132.5419 3.65331
II-5 12.77 5.44 2.13 7.6554 0.689202 147.9685 18.05938
II-6 12.80 4.99 2.12 7.5391 0.703943 135.4086 4.592301
II-7 12.69 5.02 2.15 7.5829 0.670437 136.9632 7.885112
Room Temperature: 17°C
Water Temperature: 16°C
Notes: -------
Week 9 – Unable to take moisture gain and specimen dimensions due to Christmas
holidays.
D24
Table D28. Specimen Dimensions [06 902]s - Week 10
[06 902]s Week 10
Withdrawal 2
Section thickness (mm)
Width (mm)
Thickness (mm)
Weight (g)
% Weight gain
Volume (mm3) % ∆V
II-1 12.82 4.90 2.13 7.6421 0.790008 133.8023 6.361161
II-2 12.94 4.97 2.17 7.6503 0.781188 139.5566 10.02068
II-3 12.77 5.06 2.11 7.5788 0.811408 136.3402 8.464743
II-4 12.76 4.97 2.12 7.5707 0.750569 134.4445 5.141157
II-5 12.90 5.44 2.09 7.6592 0.739182 146.6678 17.02159
II-6 12.83 5.03 2.12 7.5470 0.809468 136.814 5.677819
II-7 12.71 5.03 2.15 7.5891 0.752748 137.4523 8.270393
Room Temperature: 18°C
Water Temperature: 16°C
Notes: -------
Table D29. Specimen Dimensions [06 902]s - Week 11
[06 902]s Week 11
Withdrawal 2
Section thickness (mm)
Width (mm)
Thickness (mm)
Weight (g)
% Weight gain
Volume (mm3) % ∆V
II-1 12.85 4.90 2.13 7.6422 0.791327 134.1155 6.610056
II-2 12.94 4.97 2.15 7.6518 0.800948 138.2704 9.00666
II-3 12.77 5.06 2.14 7.5788 0.811408 138.2787 10.0069
II-4 12.76 4.97 2.13 7.5736 0.789162 135.0786 5.637106
II-5 12.90 5.44 2.09 7.6655 0.822044 146.6678 17.02159
II-6 12.83 5.03 2.12 7.5472 0.812139 136.814 5.677819
II-7 12.71 5.03 2.15 7.5897 0.760714 137.4523 8.270393
Room Temperature: 19°C
Water Temperature: 18°C
Notes: -------
D25
Table D30. Specimen Dimensions [06 902]s - Week 12
[06 902]s Week 12
Withdrawal 2
Section thickness (mm)
Width (mm)
Thickness (mm)
Weight (g)
% Weight gain
Volume (mm3) % ∆V
II-1 12.85 4.91 2.14 7.6422 0.791327 135.0201 7.329165
II-2 12.94 4.97 2.15 7.6519 0.802266 138.2704 9.00666
II-3 12.89 5.06 2.14 7.5788 0.811408 139.5781 11.04063
II-4 12.76 5.01 2.14 7.5745 0.801139 136.8051 6.987244
II-5 12.90 5.44 2.13 7.6655 0.822044 149.4749 19.26124
II-6 12.83 5.03 2.14 7.5493 0.84019 138.1047 6.67478
II-7 12.76 5.01 2.15 7.5922 0.793904 137.4443 8.264127
Room Temperature: 19°C
Water Temperature: 17°C
Notes: -------
Table D31. Specimen Dimensions [06 902]s - Week 13
[06 902]s Week 13
Withdrawal 2
Section thickness (mm)
Width (mm)
Thickness (mm)
Weight (g)
% Weight gain
Volume (mm3) % ∆V
II-1 12.85 4.93 2.16 7.645 0.828256 136.8371 8.773514
II-2 12.89 4.97 2.15 7.6546 0.837834 137.7361 8.58546
II-3 12.89 5.06 2.12 7.5825 0.860624 138.2736 10.00287
II-4 12.78 5.01 2.16 7.5767 0.830417 138.3000 8.156384
II-5 12.85 4.92 2.15 7.6670 0.841773 135.9273 8.452056
II-6 12.81 5.03 2.14 7.5503 0.853548 137.8894 6.50849
II-7 12.76 5.04 2.18 7.5938 0.815145 140.1967 10.43212
Room Temperature: 14°C
Water Temperature: 11°C
Notes: Decrease in the rate of percentage moisture gain, could be due to the drop in
temperature. Room temperature 1°C drop when compared to standard room temperature.
Water temperature 3°C colder than usual.
D26
Table D32. Specimen Dimensions [06 902]s - Week 14
[06 902]s Week 14
Withdrawal 2
Section thickness (mm)
Width (mm)
Thickness (mm)
Weight (g)
% Weight gain
Volume (mm3) % ∆V
II-1 12.86 4.93 2.16 7.6453 0.832212 136.9436 8.858162
II-2 12.87 4.93 2.14 7.6563 0.860229 135.7811 7.044202
II-3 12.81 5.06 2.16 7.5825 0.860624 140.0082 11.3828
II-4 12.78 5.01 2.13 7.5777 0.843725 136.3792 6.654212
II-5 12.83 4.92 2.15 7.6678 0.852295 135.7157 8.283259
II-6 12.81 5.03 2.14 7.5505 0.856219 137.8894 6.50849
II-7 12.73 5.00 2.18 7.5949 0.829749 138.757 9.298101
Room Temperature: 15°C
Water Temperature: 11°C
Notes: -------
Table D33. Specimen Dimensions [06 902]s - Week 15
[06 902]s Week 15
Withdrawal 2
Section thickness (mm)
Width (mm)
Thickness (mm)
Weight (g)
% Weight gain
Volume (mm3) % ∆V
II-1 12.88 4.91 2.16 7.6494 0.886286 136.6001 8.585157
II-2 12.93 4.94 2.14 7.6588 0.893163 136.6908 7.761383
II-3 12.81 5.02 2.13 7.5849 0.892548 136.9722 8.967547
II-4 12.75 4.98 2.15 7.5813 0.891633 136.5143 6.759815
II-5 12.87 4.92 2.13 7.6695 0.874655 134.8725 7.610427
II-6 12.82 5.03 2.14 7.5529 0.888277 137.997 6.591635
II-7 12.75 5.05 2.15 7.5964 0.849663 138.4331 9.042987
Room Temperature: 19°C
Water Temperature: 17°C
Notes: -------
D27
Table D34. Specimen Dimensions [06 902]s - Week 16
[06 902]s Week 16
Withdrawal 2
Section thickness (mm)
Width (mm)
Thickness (mm)
Weight (g)
% Weight gain Volume (mm3) % ∆V
II-1 12.87 4.93 2.14 7.6507 0.903432 135.7811 7.934081
II-2 12.93 4.93 2.15 7.6602 0.911606 137.0515 8.045781
II-3 12.80 5.06 2.13 7.586 0.90718 137.9558 9.750072
II-4 12.78 5.01 2.16 7.5841 0.928896 138.3000 8.156384
II-5 12.90 4.93 2.17 7.6715 0.90096 138.0055 10.11018
II-6 12.81 5.03 2.14 7.555 0.916328 137.8894 6.50849
II-7 12.76 5.03 2.18 7.5986 0.87887 139.9185 10.21301
Room Temperature: 19°C
Water Temperature: 18°C
Notes: -------
E1
Appendix E: Experimental Data from ILSS Tests
This appendix contains the ILSS values obtained. The data was obtained using the
procedure outlined in section 4.2.1.
E1. ILSS Test Values
Table E-1. Interlaminar Shear Strength [08]s configuration – Withdrawal 2months
[08]s Shear Strength (N/m2) [08]s Shear Strength (N/m2)
Dry 1 39.1 x 106 Wet 1 52.2 x 106
Dry 2 46.8 x 106 Wet 2 41.4 x 106
Dry 3 38.0 x 106 Wet 3 34.4 x 106
Dry 4 35.7 x 106 Wet 4 35.7 x 106
Dry 5 31.5 x 106 Wet 5 38.3 x 106
Dry 6 36.2 x 106 Wet 6 37.7 x 106
Dry 7 48.0 x 106 Wet 7 28.7 x 106
Table E-2. Interlaminar Shear Strength [08]s configuration – Withdrawal 4months
[08]s Shear Strength (N/m2) [08]s Shear Strength (N/m2)
Dry 1 39.1 x 106 Wet 1 47.0 x 106
Dry 2 46.8 x 106 Wet 2 45.3 x 106
Dry 3 38.0 x 106 Wet 3 44.9 x 106
Dry 4 35.7 x 106 Wet 4 36.5 x 106
Dry 5 31.5 x 106 Wet 5 26.7 x 106
Dry 6 36.2 x 106 Wet 6 35.8 x 106
Dry 7 48.0 x 106 Wet 7 31.2 x 106
Average Dry [08]s Shear Strength = 36.14 x 106 N/m2
Average Wet II [08]s Shear Strength = 37.5 x 106 N/m2
Average Wet I [08]s Shear Strength = 40.23 x 106 N/m2
Increase of ± 3.76% in Interlaminar Shear Strength of [08]s
Increase of ± 11.3 % in Interlaminar Shear Strength of [08]s
E2
Table E-3. Interlaminar Shear Strength[06 902]s configuration – Withdrawal 2months
[06 902]s Shear Strength (N/m2) [06 902]s Shear Strength (N/m2)
Dry 1 18.4 x 106 Wet 1 28.9 x 106
Dry 2 19.3 x 106 Wet 2 23.8 x 106
Dry 3 19.1 x 106 Wet 3 21.6 x 106
Dry 4 23.4 x 106 Wet 4 21.7 x 106
Dry 5 21.1 x 106 Wet 5 25.9 x 106
Dry 6 20.2 x 106 Wet 6 21.9 x 106
Dry 7 19.3 x 106 Wet 7 30.9 x 106
Table E-4. Interlaminar Shear Strength [06 902]s configuration – Withdrawal 4months
[06 902]s Shear Strength (N/m2) [06 902]s Shear Strength (N/m2)
Dry 1 18.4 x 106 Wet 1 22.7 x 106
Dry 2 19.3 x 106 Wet 2 29.2 x 106
Dry 3 19.1 x 106 Wet 3 17.7 x 106
Dry 4 23.4 x 106 Wet 4 21.7 x 106
Dry 5 18.8 x 106 Wet 5 25.0 x 106
Dry 6 20.2 x 106 Wet 6 23.3 x 106
Dry 7 21.6 x 106 Wet 7 23.3 x 106
Average Dry [06 902]s Shear Strength = 19.5 x 106 N/m2
Average Wet I [06 902]s Shear Strength = 23 x 106 N/m2
Average Wet II [06 902]s Shear Strength = 23.22 x 106 N/m2
Increase of ± 17.65% in Interlaminar Shear Strength of [06 902]s to Wet I
Increase of ± 18.73% in Interlaminar Shear Strength of [06 902]s to Wet II
E3
E2. Force versus Extension graphs [08]s
Figure E-0-1. Force versus Extension graph [08]s configuration - Dry
Figure E-0-2. Force versus Extension graph [08]s configuration – Wet I – withdrawal 2 months
0
500
1000
1500
2000
2500
3000
0
0.05
4
0.10
8
0.16
2
0.21
6
0.27
0.32
4
0.37
8
0.43
2
0.48
6
0.54
0.59
4
0.64
8
0.70
2
0.75
6
0.81
0.86
4
0.91
8
0.97
2
1.02
6
1.08
1.13
4
1.18
8
1.24
2
1.29
6
1.35
1.40
4
Forc
e (
N)
Extension (mm)
0
500
1000
1500
2000
2500
3000
00.
056
0.11
20.
168
0.22
40.
280.
336
0.39
20.
448
0.50
40.
560.
616
0.67
20.
728
0.78
40.
840.
896
0.95
21.
008
1.06
41.
121.
176
1.23
21.
288
1.34
41.
41.
456
Forc
e (
N)
Extension (mm)
E4
Figure E-0-3. Force versus Extension graph [08]s configuration – Wet II – withdrawal 4 months
0
500
1000
1500
2000
2500
3000
3500
0
0.05
6
0.11
2
0.16
8
0.22
4
0.28
0.33
6
0.39
2
0.44
8
0.50
4
0.56
0.61
6
0.67
2
0.72
8
0.78
4
0.84
0.89
6
0.95
2
1.00
8
1.06
4
1.12
1.17
6
1.23
2
1.28
8
1.34
4
1.4
1.45
6
Forc
e (
N)
Extension (mm)
E5
E3. Force versus Extension graphs [06 902]s
Figure E-0-4. Force versus Extension graph [06 902]s configuration – Dry
Figure E-0-5. Force versus Extension graph [06 902]s configuration – Wet I – withdrawal 2 months
0
200
400
600
800
1000
1200
1400
0
0.04
8
0.09
6
0.14
4
0.19
2
0.24
0.28
8
0.33
6
0.38
4
0.43
2
0.48
0.52
8
0.57
6
0.62
4
0.67
2
0.72
0.76
8
0.81
6
0.86
4
0.91
2
0.96
1.00
8
1.05
6
1.10
4
1.15
2
1.2
1.24
8
1.29
6
Forc
e (
N)
Extension (mm)
0
200
400
600
800
1000
1200
1400
1600
0
0.03
6
0.07
3
0.10
9
0.14
5
0.18
1
0.21
8
0.25
4
0.29
0.32
6
0.36
3
0.39
9
0.43
5
0.47
1
0.50
8
0.54
4
0.58
0.61
6
0.65
3
0.68
9
0.72
5
0.76
1
0.79
8
0.83
4
0.87
0.90
6
0.94
3
0.97
9
Forc
e (
N)
Extension (mm)
E6
Figure E-0-6. Force versus Extension graph [06 902]s configuration – Wet II – withdrawal 4 months
0
200
400
600
800
1000
1200
1400
1600
1800
0
0.04
0.08
0.12
0.16 0.2
0.24
0.28
0.32
0.36 0.4
0.44
0.48
0.52
0.56 0.6
0.64
0.68
0.72
0.76 0.8
0.84
0.88
0.92
0.96
1
1.04
1.08
Forc
e (
N)
Extension (mm)
E7
E3: Statistical Analysis
This appendix contains the results included for analysis after a preliminary examination of
the fracture surfaces to exclude any outliers based on a number of variables such as depth
of the notches.
E.3.1. Standard deviation and mean values for [08]s specimens
Figure E-0-7. ILSS Values for [0] specimens - Dry
Standard Deviation: 2.9 x 106 N/m
2
Mean: 36.14 x 106
N/m2
0
5000000
10000000
15000000
20000000
25000000
30000000
35000000
40000000
45000000
1 2 3 4 5
Actual
Mean
E8
Figure E-0-8. ILSS Values for [0] specimens – Wet I - withdrawal 2 months
Standard Deviation: 2.6 x 106 N/m
2
Mean: 37.5 x 106
N/m2
FigureE-0-9. ILSS Values for [0] specimens – Wet II - withdrawal 4 months
Standard Deviation: 5.3 x 106 N/m
2
Mean: 41.95 x 106
N/m
31000000
32000000
33000000
34000000
35000000
36000000
37000000
38000000
39000000
40000000
41000000
1 2 3 4 5
Actual
Mean
0
5000000
10000000
15000000
20000000
25000000
30000000
35000000
40000000
45000000
50000000
1 2 3 4 5
Actual
Mean
E9
E.3.2. Standard deviation and mean values for [06 902]s specimens
Figure E-0-10. ILSS Values for [06 906]s specimens – Dry
Standard Deviation: 0.9 x 106 N/m
2
Mean: 19.55 x 106
N/m2
17000000
17500000
18000000
18500000
19000000
19500000
20000000
20500000
21000000
21500000
1 2 3 4 5 6
Actual
Mean
E10
Figure 0-11. ILSS Values for [06 906]s specimens – Wet I - withdrawal 2 months
Standard Deviation: 1.8 x 106 N/m
2
Mean: 23 x 106
N/m2
Figure 0-12. ILSS Values for [06 906]s specimens – Wet II - withdrawal 4 months
Standard Deviation: 1.2 x 106 N/m
2
Mean: 23.22 x 106
N/m2
0
5000000
10000000
15000000
20000000
25000000
30000000
1 2 3 4 5
Actual
Mean
20000000
21000000
22000000
23000000
24000000
25000000
26000000
1 2 3 4 5
Actual
Mean
F1
Appendix F: SEM Micrographs
This appendix contains the micrographs obtained using Scanning Electron Microscopy. The
procedure outlined in section 4.4 was used to obtain the images.
Appendix F1. Fracture surface of dry [08]s specimens at magnification
x100
Figure F-1. Fracture surface of a dry [08]s specimen - magnification x100
F2
Figure F-2. Fracture surface of a wet I [08]s specimen - magnification x100
Figure F-3. Fracture surface of a wet II [08]s specimen - magnification x100
F3
Appendix F2. Fracture surface [06 902]s specimens at magnification x100
Figure F-4. Fracture surface of a dry [06 902]s specimen - magnification x100
Figure F-5. Fracture surface of a wet I [06 902]s specimen - magnification x100
F4
Figure F-6. Fracture surface of a wet II [06 902]s specimen - magnification x100
F5
Appendix F3. Fracture surface of dry [08]s specimens at magnification
x500
Figure F-7. Fracture surface of a dry [08]s specimen - magnification x500
Figure F-8. Fracture surface of a wet I [08]s specimen - magnification x500
F6
Figure F-9. Fracture surface of a wet II [08]s specimen - magnification x500
F7
Appendix F4. Fracture surface [06 902]s specimens at magnification x500
Figure F-10. Fracture surface of a dry [06 902]s specimen - magnification x500
Figure F-11. Fracture surface of a wet I [06 902]s specimen - magnification x500
F8
Figure F-12. Fracture surface of a wet II [06 902]s specimen - magnification x500
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