Impact and Flexural Strengths of Carbon-Carbon Composites ... · of the two properties points to one name, Carbon-carbon composites (CCC), which has proven to be the material of future,

The Journal of Advances in Mechanical and Materials Engineering 2018; 1(1): 1-11.

1

Research Article Open Access

Impact and Flexural Strengths of Carbon-Carbon Composites Prepared

by Preformed Yarn Method

Anilas K1, AO Surendranathan2*, Sunil Kumar BV3, J Gururaja Rao4

1PG scholar, 2Professor, Department of Metallurgical and Materials Engineering, National Institute of Technology

Karnataka, Surathkal, India. 3Assistant Professor, Department of Mechanical Engineering, Canara Engineering College, Mangalore, VTU,

Karnataka, India. 4Scientist ‘E’, High Temperature Composite Centre, Advanced Systems Laboratory, DRDO, Hyderabad, India.

Abstract

Carbon-carbon composites, due to their unique properties like high specific strength, stiffness and in plane

toughness as well as refractory properties like retention of mechanical properties at extremely high

temperatures of the order of 3000oC, find application as structural materials in space vehicles, heat shields,

rocket nozzles and aircraft brakes. Properties like biocompatibility and chemical inertness have led to new

applications in medicine industry. Advanced fabrication techniques like Preformed Yarn (PY) method showed

exceptional values for specific strength and fracture toughness than conventional methods already available.

The present study centres on the PY method where a PY (Preformed Yarn) machine is the backbone, to

synthesize preformed yarns (PYs). PYs were synthesised from carbon fibre filaments, used as reinforcement,

and coke and pitch, used as matrix. Upon fabrication of PYs of sufficient quantity, hot pressing, pitch

impregnation and heat treatment (carbonization and graphitization) were done at sufficiently higher

temperatures to get the final CCC. Characterization by XRD (X-Ray diffraction) and SEM (scanning electron

microscope) was done. Impact strength and flexural strength were tested and studied with reference to the

previous work in this field. The CCC fabricated by PY method was found to have superior properties than other

fabrication techniques, however, optimization of the method is still possible. Increasing the fibre content and

THE JOURNAL OF ADVANCES IN MECHANICAL AND MATERIALS ENGINEERING

Journal Home Page: https://uniquepubinternational.com/journal-advances-mechanical-

materials-engineering-jamme/

Copyright: © 2018 Unique Pub International (UPI). This

is an open access article under the CC-BY-NC-ND License

(https://creativecommons.org/licenses/by-nc-nd/4.0/).

Correspondence to: Surendranathan AO, Professor,

Department of Metallurgical and Materials Engineering,

National Institute of Technology Karnataka, Surathkal,

India.

Email: [email protected]

Funding Source(s): NA How to Cite: Anilas K, Surendranathan AO, Sunil Kumar

BV, Gururaja Rao J. Impact and Flexural Strengths of

Carbon-Carbon Composites Prepared by Preformed Yarn

Method. The Journal of Advances in Mechanical and

Materials Engineering 2018; 1(1): 1-11.

Editorial History:

Received : 16-09-2018, Accepted: 12-12-2018,

Published: 15-12-2018


2

attaining the maximum possible level of graphitization are the key points to be noted for the fabrication of best

CCC.

Key words: Carbon fibre, Coke, Pitch impregnation, Graphitization, Carbon-Carbon Composites.

1. Introduction

The night sky and space have always been a wonder to human beings. Humans have been curious about the

vast infinity they see above them. The realization of his most beautiful dream kick-started by the launch of

Sputnik 1 in 1957, followed by a series of milestones which included the first space expedition by a human

being, Yuri Gagarin in 1961 (first human to orbit earth, altitude of 327km). The prominent concern of scientists

then was to develop a safe material, to be used for the structural applications in aerospace. Aluminium was the

first material to serve the purpose, which over evolution, was replaced by superior materials. Aerospace

application demands the material to be light weight, yet strong enough to take up harsh loading. A combination

of the two properties points to one name, Carbon-carbon composites (CCC), which has proven to be the

material of future, with its exceptional properties. CCC, despite of their generally high cost, is a key material in

today's launch vehicles and heat shields for the re-entry phase of spacecraft. It is widely used in solar panel

substrates, antenna reflectors and yokes of spacecraft. It is also used in payload adapters, inter-stage structures

and heat shields of launch vehicles. Furthermore, disk brake systems of airplanes and racing cars use CCC, and

the composite material with carbon fibres and silicon carbide matrix has been introduced in luxury vehicles and

sports cars. The Boeing 787 and Airbus A350 structures including the wings and fuselage are composed largely

of composites mainly, CCC. CCC materials have also become more common in the realm of medicine like

orthopaedic surgery.

Conventional fabrication techniques of CCC used carbon fibres based on rayon/PAN/pitch as primary carbon. To

fill the small gaps between the fibres two routes were used - Gas phase impregnation or chemical vapour

deposition (CVD) process and liquid phase impregnation process [1]. Tongshik CHANG [2] fabricated CCC by

simple hot pressing of pulverized coke powders as matrix, carbonaceous bulk mesophase pitch as binder and

carbon fibres as reinforcements. A few modifications to the conventional liquid phase impregnation were done

by Windhorst [3] by pre-impregnating fibres with resin or pitch and performing hot isostatic pressure

impregnation carbonization (HIPIC). V. Ramani [4] developed CCC for nuclear reactors by impregnation method

by PAN preforms and phenol formaldehyde resin. A more efficient technique was developed by N. Hirotaka [5],

known as the Preformed Yarn method, which gave superior results than the above mentioned conventional

methods and their modifications. Property enhancement techniques used in the fabrication of CCC and different

carbon composites like application of temperature [6], densification [7], increasing the number of pitch/resin

impregnation cycles [8], using carbon nanotubes and carbon nanofibres as reinforcements [9], using carbon

fibre felt as reinforcements [10], using different fibre architecture [11], growing multi walled carbon nanotubes

on woven carbon fibre [12], graphene/graphite-based conductive polyamide12 interlayer between reinforcement

layers [13], microwave curing [14], dissolvable thermoplastic fibres in the reinforcement preform [15], silk

fibroin nanofibres as reinforcements [16] and fibre sizing [17] point out the probability of fabrication of superior

CCC in the future.


3

2. Experimental

2.1. Fabrication of Preformed Yarns

Preformed Yarn (PY) method was chosen over conventional manufacturing techniques, for the fabrication of

CCC, as this method had proven its worth with its exceptional results in terms of properties attained by the

fabricated CCC [18-20]. However, suitable optimization of the method was done for the betterment of results.

Figure 1. The PY machine.

Carbon fibre (reinforcement), coke and pitch (matrix) blended in powdered form and polyolefine heat shrinkable

tube as sleeve material were fed to the PY machine (Figure 1). A combination of 120 °C as a burner

temperature and 12 rpm as the machine operating speed yielded preformed yarns at a rate of 1metre per

minute. The PY machine was run for sufficient time to produce the required length of PYs. We managed to

produce about 300m of PYs. The composition of the prepared preform is as given in table 1.

Table 1. Composition of preformed yarn.

Description

Matrix (wt %) Fibre

(wt%)

Sleeve

(wt%) Pitch and Coke Together

(wt%) Pitch Fraction in Matrix

(wt%)

Preformed Yarn (PY) 54.13 50.00 35.49 10.37

PYs produced were taken for the next stage of fabrication, the steps of which are listed below. The processes

mentioned in these steps were arrived at, after suitable optimizations done to those followed by P. Naik [18-20].

1. Chopped PYs were kept uni-directionally in a mould and subjected to pressing in a 100-ton hydraulic

press. A pressure of 25 ton was applied at 350°C gradually in 4h. The sleeve material was burned off

(porosity might have occurred) at this stage and the pitch got softened and blended with coke, which then

got adhered to the carbon fibre more efficiently when pressure was applied.

2. Pitch impregnation was done at 250°C and 0.1 MPa for 24h. More pitch got penetrated into the pores

and voids created at step 1.


4

3. Carbonization: Hot Isostatic Pressing (HIP) was done at 800-1000°C and 90-100MPa. The peak

temperature was maintained for at least 1h. The conversion of pitch to coke was completed at this stage.

4. Graphitization: It was done above 2500°C and 1 atm, in which the peak temperature was maintained

for at least 1 h. Coke conversion to graphite was completed, yielding the final composite material.

The above mentioned steps were done at Advanced Systems Laboratory (ASL), Defence Research and

Development Organization (DRDO), Hyderabad, India.

2.2. Characterization of CCC

2.2.1. Scanning Electron Microscope (SEM)

The SEM micrographs of CCC samples fabricated were obtained using the scanning electron microscope (Model:

JSM-6380LA, Make: JEOL Japan). The surfaces of the samples were sputtered with an even thin film of gold

powder to improve the conductivity of the surface. The images were taken in secondary electron modes and

suitable accelerating voltage.

2.2.2. X-RD Analyzer

X-ray diffraction of the fabricated samples were performed using the diffractometer (Model: JDX 8P, Make: JEOL

Japan). X-RD patterns were recorded from 10o to 60o at a speed of 2o per minute using copper radiation, CuKα

(λ=1.542 A.U.), with an accelerating voltage of 40KV and 30mA.

2.3. Mechanical Properties

2.3.1. Flexural Properties

Three-point bending test was carried out using computerized universal testing machine (STM 50KN, Make:

United) in accordance with ASTM D 790 standard at a cross head speed of 2mm/min. The dimensions of test

specimen are 3.2 mm x12.7 mm x 125 mm, in accordance to ASTM D 790 (Figure 2(a)).

12.7 mm (a) 125mm 3.2mm

10 mm 55 mm 10mm (b)

Figure 2. ASTM specified standard dimensions for (a) Flexural test specimen (b) Impact test specimen.

2.3.2. Impact Strength

Un-notched Charpy impact tests were conducted on each specimen using impact tester (Make: JUSTY).

According to ASTM A 370 the standard dimension of test specimen is 10mm X 10mm X 55mm (Figure 2(b)).


5

2.4. Density as an Important Property

As far as CCC is concerned, in applications like aerospace, the density plays an important role. The expected

density of this class of materials is between 1.6-1.98g/cc and usually a density above 1.7g/cc is accepted for

aerospace applications.

3. Results and Discussion

3.1. SEM Analysis of CCC

In very few areas, we can see the absence of carbonaceous matrix around the fibre. This absence of binder

around the fibres can be due to factors like hot pressing, by which fibres get disoriented slightly.

Figure 3 (a) and (b). SEM micrographs showing good fibre-matrix bonding viewed at 2 different

magnifications.

Almost all the carbon fibres were oriented uni-directionally as shown in figure 4. Due to the effect of hot

pressing, some of the fibres can be seen to be aligned in other directions and some others in oval shape with a

difference in diameters. Further, breakage and elongation of fibres can also be seen as in figure 5.

Figure 4(a) and (b). SEM micrograph showing unidirectional orientation of carbon fibre viewed at 2 different

magnifications.


6

Figure 5(a) and (b). SEM micrograph showing difference in fibre diameter due to elongation in 2 different

samples.

The fractured surface of the CCC is as shown in figure 6, which clearly reveals a brittle behaviour of fracture.

Fracture can be explained to have occurred by energy consuming mechanisms like fibre pull-out and fibre

debonding, which are as shown in figure 7-8.

(6) (7) (8)

Figure 6. SEM micrographs of fractured surface under Charpy test; Figure 7. SEM micrograph showing fibre

pullout; Figure 8. SEM micrograph showing fibre debonding.

3.2. XRD Analysis of CCC

The XRD analysis of the fabricated sample

2ϴ (degree) = 26.228o

Full width half maximum (FWHM) (degree) = 0.312

d002 spacing (nm) = 0.3395

t (nm) = 4.567

The XRD patterns of raw materials are as shown in figures 9-11 and that of the fabricated sample in figure 12.

The amorphous carbon present in the raw materials was converted into crystalline graphite in the prepared

samples (Figure 12). By comparing with JCPDF it is concluded that carbon is present in graphite form for the

fabricated CCC sample at 26.228o with a ‘d’ spacing of 3.395 A.U. With this it can be concluded that

graphitization initiated is almost complete in the sample. The glassy phases reveal the presence of small

amounts of amorphous phase, which could be understood from XRD peak width and serration.


7

Figure 9. XRD pattern of the raw petroleum coke. Figure 10. XRD pattern of the raw coal tar pitch.

(11) (12) Figure 11. XRD pattern of as received fibre (6K) before processing; Figure 12. XRD pattern of CCC fabricated

sample.

3.3. Analysis of Properties

3.3.1. Density

Densities of the samples after different stages were calculated and are tabulated in Table 2. Fabricated samples

after two cycles of pitch impregnation, carbonisation and graphitization are as shown in (Figure 13).

Figure 13. Fabricated samples before machining.


8

Table 2. Density of PY at different stages.

Sample No Length (cm) Width (cm) Thickness (cm) Weight (g) Density (g/cc)

Moulded state

1 10.24 9.93 2.82 249.80 0.89

2 14.73 1.99 1.80 44.10 0.82

3 12.00 12.00 1.54 137.50 0.62

After first cycle of pitch impregnation, HIP and graphitization

1 10.09 8.94 1.79 217.86 1.35

2 15.01 1.87 1.55 49.46 1.23

3 12.01 10.93 1.09 159.69 1.12

After second cycle of pitch impregnation, HIP and graphitization

1 10.13 8.96 1.14 162.50 1.57

2 15.09 1.89 0.98 42.84 1.54

3 12.07 11.05 1.17 206.20 1.35

Closely observing the trend of increase of density, one can conclude that an extra cycle of pitch impregnation,

HIP and graphitization would give an increased density. Previously, P. Naik [19] achieved a density of 1.55 g/cc

after completing three cycles for fibre 30 wt%. Comparing with this, and taking into consideration that the

extend of graphitization is beyond the value that was previously achieved, we can conclude that the value of the

density would surely cross the value of 1.7g/cc to a reasonably excellent one, if a third cycle of pitch

impregnation is completed.

3.3.2. Flexural Strength

For an average load of 0.38KN and displacement 0.969mm, the average of the Flexural strength readings

obtained for different samples is 148.76 MPa and that of Flexural Modulus is 35.88 GPa. A sample test report is

as shown in figure 15 for one of the samples (Figure 14).

Figure 14. Test specimens for flexural test.

Previously, P. Naik [19] obtained a value of 184MPa. Considering the fact that the value obtained here is only

after two cycles of pitch impregnation, HIP and graphitization, the obtained value is appreciable while comparing

with the previously obtained value, which was after three cycles. Flexural modulus, which is now 35.88 GPa, is

very close to that obtained previously (35.39 GPa) by P. Naik [19].


9

(15) (16)

Figure 15. Test report for the sample’s flexural test. Figure 16. Samples after Charpy impact test.

3.3.3. Impact Strength

The average impact strength of the three samples (Figure 16) obtained is 20 KJ/m2. P. Naik [20] obtained an

impact strength value of 22 KJ/m2 for the fibre weight % of 30%. Comparing with the results obtained by P.

Naik [20], it is observed that the impact strength of the CCC is very much in the increasing trend. Thus it can be

concluded that an increase in the heat treatment temperature, especially the graphitization temperature, has a

positive effect on the impact strength of the fabricated CCC. Just in two cycles of pitch impregnation, HIP and

graphitization, a value close to that obtained after three cycles was managed. In general, in addition to the

amount of fibre content, as suggested by P. Naik [20], the extent of graphitization also enhances the impact

properties of CCC.

4. Conclusions

The optimization of the PY machine for the fabrication of preformed yarns was successfully done and CCC was

fabricated. Characterization and analysis of properties of the fabricated CCC were carried out. From the results

and discussion, the following conclusions are drawn:

With the successful completion of just two cycles of pitch impregnation, HIP at 800-1000oC and

graphitization at temperatures above 2500oC, CCC was successfully fabricated.

From the impact test, it is concluded that with a graphitization extending beyond 2500oC, CCC with

impact strength value of 20 KJ/m2 can be fabricated, which is very close to previously obtained value of

22 KJ/m2. The value can still be improved by completing the third cycle of pitch impregnation, HIP and

graphitization as well as by increasing the fibre weight%.


10

From the density, flexural and impact studies, it was observed that not only the fibre weight %

contributes to the improvement of the properties, but also the extent of heat treatment, especially

graphitization (above 2500oC), which was not attained in previous studies (it was below 2500oC).

Densification of CCC by pitch impregnation is vital in the fabrication as without proper pitch

impregnation, CCC with inferior density and properties would be fabricated.

5. Conflicts of Interest

The author(s) report(s) no conflict(s) of interest(s). The author along are responsible for the content and writing

of the paper.

6. Acknowledgments

NA

7. References

1. Rohini Devi G, Rama Rao K. Carbon-carbon composites: An overview. Defence Science Journal 1993;

43(4): 369-383.

2. Tongshik C, Akimitsu O. Fabrication of carbon-carbon composites using carbon fibres impregnated with

resin and their mechanical properties.Transactions ISIJ 1987; 27: 229-238.

3. Windhorst T, Blount G. Carbon-carbon composites: a summary of recent developments and

applications.Materials & Design1997; 18(1): 11-15.

4. RamaniV, Sathiyamoorthy D, Tyagi AK. Development of Carbon / Carbon Composites for Nuclear Reactor

applications. BARC Newsletter2012; 325: 16-20.

5. Hirotaka N, Takao N, Hidefumi H. Manufacture of unidirectional carbon fiber reinforced carbon composites

by Preformed-Yarn Method.1999; 1999(186): 7-12.

6. KenG, Hiroshi O, Hiroshi H, Hiroaki I, Yasua K. Tensile strength and creep behavior of carbon-carbon

composites at elevated temperatures. 16th International conference on composite materials, 2007, pp. 1-6.

7. Hatta H, Suzuki K, Shigei T, Somiya S, Sawada Y. Strength improvement by densification of C/C

composites. Carbon 2001; 39(1): 83-90.

8. Jan C, Stainislaw B, Powroznik A. Mechanical Properties of Carbon-Carbon Composites. Ceramic

international 1993; 19(4): 251-257.

9. Shinn-ShyongT, Yu-Hun L. Mechanical properties of carbon-carbon composites reinforced with carbon nano

tubes or carbon nanofibers. 16th International conference on composite materials, Tokyo, Japan, 2007, pp.

1-5.

10. Kurumada A, Iwaki H, Komatsu Y. Tensile Properties and Fracture Toughness of Carbon-Fiber Felt

Reinforced Carbon Composites At high temperature. 1989; 27(6): 791-801.

11. Neumeister J, Jansson S, Leckie F. The effect of fiber architecture on the mechanical properties of

carbon/carbon fiber composites. Acta Materialia 1996; 44(2): 573-585.

12. Kepple KL, Sanborn GP, Lacasse PA, Gruenberg KM, Ready WJ. Improved fracture toughness of carbon

fiber composite functionalized with multi walled carbon nanotubes. Carbon 2008; 46(15): 2026-2033.

13. Barjasteh E, Sutanto C, Reddy T, Vinh J. A graphene/graphite-based conductive polyamide 12 interlayer for


11

increasing the fracture toughness and conductivity of carbon-fiber composites. Journal of Composite

Materials2017; 51(20): 2879-2887.

14. Zhou J, Li Y, Li N, Hao X.Enhanced interlaminar fracture toughness of carbon fiber/bismaleimide

composites via microwave curing. Journal of Composite Materials 2017; 51(18): 2585-2595.

15. Wong DWY, Lin L, McGrail PT, Peijs T, Hogg PJ. Improved fracture toughness of carbon fibre/epoxy

composite laminates using dissolvable thermoplastic fibres. Composites Part A: Applied Science and

Manufacturing 2010; 41(6): 759-767.

16. Cuong VM, Hyoung JC. Enhancement of interlaminar fracture toughness of carbon fiber/epoxy composites

using silk fibroin electro-spun nanofibers. Polymer Plastics Technology and Engineering 2016; 55(10):

1048-1056.

17. Wen BL, Shu Z, Bichen L, Fan Y, Wei CJ, Li FH, Rong GW. Improvement in interfacial shear strength and

fracture toughness for carbon fibre reinforced epoxy composite by fibre sizing. Polymer composites 2014;

35(3): 482-488.

18. Naik P, Ibrahim M, Surendranathan A, Mujeebu M. Development and characterization of carbon-carbon

composite for aircraft brake pad using preformed yarn method. World Journal of Engineering 2011; 8(3):

259-266.

19. Naik P, Londe NV, Surendranathan AO, Jayaraju T. Carbon-carbon composites by preformed yarn

method.International Journal of Mechanical and Materials Engineering 2011; 6(1): 133-139.

20. Naik PS, Surendranathan AO, Ravishankar KS. Preparation of yarn based carbon-carbon composites and

their properties. International Journal of Science Technology and Management 2015; 4(1): 156-163.

Documents

Impact and Flexural Strengths of Carbon-Carbon Composites ... · of the two properties points to one name, Carbon-carbon composites (CCC), which has proven to be the material of future,