View
4
Download
0
Category
Tags:
Preview:
DESCRIPTION
mech
Citation preview
MEK4540-2012-1.1
MEK4540 Komposittmaterialer og konstruksjoner Composite materials and structures
Innledning materialer ensrettede kompositter Introduction materials unidirectional composites
MEK4540-2012-1.2
MEK4540 Teaching schedule Normally lectures will be on Wednesdays from 12.15-14.00 and
practice sessions will be on Thursdays from 12.15-14.00.
However, there will be several deviations from this:
Lecture no. 2 will be held on Thursday 23.08.2012 in place of the practice session.
There will be no lecture on Wednesday 29.08.2012.
There will be a practice session on Thursday 30.08.2012.
There will also be deviations in September and early October.
The full schedule will be published within 1-2 days.
MEK4540-2012-1.3
Preliminaries Language:
PowerPoint presentations in English Text books in English Norwegian + English technical terms will be provided where possible Spoken language Norwegian or English Assignments (obligs) handed out in English Students may hand in solutions in English or Norwegian Written or oral examination in Norwegian or in English if requested
Text books: Main text:
B.D. Agarwal, L.J. Broutman and K. Chanrashekhara: Analysis and Performance of Fiber Composites, 3rd ed.
Composite plates additional material: D. Zenkert and M. Battley: Foundations of Fibre Composites Ch. 5 and parts of Ch. 8 to be handed out
Sandwich beams and plates: D. Zenkert: Introduction to Sandwich Construction (student edition KTH)
MEK4540-2012-1.4
Course content Kursets innhold Introduction and definitions Component materials Unidirectional composites Orthotropic lamina (plies)
and laminates Laminated plates (bending
and buckling) Composites in ANSYS Sandwich materials Sandwich beams and plates Joints Short fibre composites Production methods Mechanical testing Design criteria and rules
Innledning og definisjoner Materialkomponenter Ensrettede kompositter Ortotrope lag og laminater Laminerte plater (byning og
knekning) Kompositter i ANSYS Sandwichmaterialer Sandwichbjelker og -plater Sammenfyninger Kortfiberkompositter Produksjonsmetoder Mekanisk prving Dimensjonering og regelverk
MEK4540-2012-1.5
Definitions A composite material is a material that consists of one or more
discontinuous components (particles/fibres/reinforcement) that are placed in a continuous medium (matrix)
In a fibre composite the matrix binds together the fibres, transfers loads between the fibres and protects them from the environment and external damage.
The fibres carry the loads.
MEK4540-2012-1.6
Main classes
Particulate composites Various geometrical shapes (cubes, spheres, flakes, etc.) Various materials (rubber, metal, plastics, etc.) Have generally low strength. Will not be treated further in this course.
Fibre composites Discontinuous or Continuous
See next slide for further divisions
MEK4540-2012-1.7
Classification of composite materials From Agarwal, Broutman & Chanrashekhara
and multi-layered composites having same properties in each layer
Layers with different materials
MEK4540-2012-1.8
Microscopy
MEK4540-2012-1.9
Composites properties
UD = unidirectional = ensrettet
QI = quasi-isotropic
= kvasi-isotrop
MEK4540-2012-1.10
Applications
MEK4540-2012-1.11
Offshore/subsea Tension leg, tether
Riser
Subsea protection cover
MEK4540-2012-1.12
Offshore/subsea
MEK4540-2012-1.13
Ships/boats
MEK4540-2012-1.14
Naval ships
MEK4540-2012-1.15
Sports and leisure equipment
MEK4540-2012-1.16
Cars
MEK4540-2012-1.17
Trains (Flytoget)
MEK4540-2012-1.18
Aircraft
MEK4540-2012-1.19
Composites in Airbus designs
http://www.mscsoftware.com/events/vpd2007/emea/presentations/Session-2A-AIRBUS-Bold.pdf Source:
MEK4540-2012-1.20
Composites in Airbus designs
http://www.mscsoftware.com/events/vpd2007/emea/presentations/Session-2A-AIRBUS-Bold.pdf Source:
MEK4540-2012-1.21
Materials in Boeing 787 Dreamliner
http://www.boeing.com/commercial/aeromagazine/articles/qtr_4_06/article_04_2.html Source:
MEK4540-2012-1.22
Aircraft development over the years
MEK4540-2012-1.23
Wind energy
The blades can be as long as 62 m
MEK4540-2012-1.24
Buildings and bridges
MEK4540-2012-1.25
British naval vessels in GRP
HMS Wilton
HMS Sandown
GRP is used here for its non-magnetic properties
MEK4540-2012-1.26
Sandown class mine-hunter
Midship section
MEK4540-2012-1.27
Sandwich catamarans (SES)
Midship section
MEK4540-2012-1.28
Visby Class Swedish Navy
72 m long CFRP sandwich with PVC core
MEK4540-2012-1.29
Materials glass fibres
Types: E-glass (+ S-glass, C-glass and D-glass) Production method
Spun from molten glass
Properties Low cost Moderately high strength Low stiffness Low wear resistance Sensitive to moisture Sizing (coating / surface preparation): 2 types/purposes:
To protect the fibres and keep them together during further processing (weaving etc.). Removed before use.
To improve adhesion (also called coupling agents) organofunctional silanes
MEK4540-2012-1.30
Materials carbon fibres Carbon and graphite fibres
Graphite fibres: 99% Carbon Carbon fibres: 8095% Carbon
Production Organic fibres: PAN, rayon and pitch Stretched and stabilised at 200C Pyrolysis at 1500C (inert atmosphere) Grafitisation at 3000C (inert atmosphere)
strong covalent bonds in longitudinal direction of fibre.
Important to note Carbon fibres can be of several types, with widely differing
properties. Normally supplied with sizing for use with epoxy resins use
with polyester and vinylester requires special sizing.
MEK4540-2012-1.31
Materials other fibre types
Aramid (Kevlar, Twaron) Aromatic polyamide Spun from solution in acid
HPPE High performance polyethylene UHMW-PE ultra-high-molecular-weight polyethelene Spun from solution and then stretched Dyneema and Spectra Properties roughly similar to aramid
Boron, SiC
MEK4540-2012-1.32
Fibre properties
Tensile modulus [GPa]
Tensile strength [MPa]
Tensile strain at failure [%]
Density [g/cc]
E-glass 72 2000 -2500 3 2.5
High-stiffness carbon
500-800 2100 0.9-1.8 2
High-strength carbon
250-350 3100-4500 0.3-0.4 1.8
Kevlar 49 124 3600 1.4
UHMWPE 118 2500 0.97
NB: Carbon fibres are available with a wide range of properties!
MEK4540-2012-1.33
Reinforcement architecture UD fabric or tape Multiaxial non-crimp knitted fabric
straight fibres i layers with defined directions, stitched together
Woven fabric fibres in 0/90 directions, not straight
Chopped strand mat (CSM) short fibres randomly oriented
Continuous strand mat long fibres randomly oriented
MEK4540-2012-1.34
Matrix materials polymers
Poly = many Mer = part
E.g. polyethylene [- CH2 CH2 -]n
Linear
Branched
Cross-linked
MEK4540-2012-1.35
Matrix materials
Thermoplastics Polyethylene (PE), polypropylene (PP) (=polyolefin), PMMA, PVC,
PS, ABS, PC, POM, PET, TPU Linear or branched molecule chains (are not chemically bound to
each other) Can be melted down and re-used
Thermosets Polyester (unsaturated), Epoxy, Vinylester, Polyimide, Phenolic Cross linked chains are chemically bound to each other Cannot be melted down and re-used Supplied as prepolymer (resin) which hardens when initiator or
hardener is added.
MEK4540-2012-1.36
Polymer mechanical properties temperature dependence
Thermoplastic, amorphous Linear or branched chains Transparent PS, PC, PMMA Can only be used at T
MEK4540-2012-1.37
Unsaturated polyester Prepolymer: Linear chain dissolved in styrene
Styrene participates in curing process and reduces viscosity Addition of inhibitors and accelerators
Production of polyester resin Saturated dibasic acid
Phthalic acid anhydride most used, cheapest Isophthalic acid Adipin acid flexibility
Unsaturated dibasic acid Fumaric acid Maleic acid
Glycol Propylene glycol most used Ethylene or diethylene glycol
Curing: Styrene, retarded by inhibitor, addition of initiator results in cross linking
Addition polymerisation, no by-products, EXOTHERM Styrene HMS for open processes
Tighter cross-linking gives higher Tg, but a more brittle material
MEK4540-2012-1.38
Epoxy
Epoxy group Linear prepolymer (resin)
Ordinary Epichlorohydrin + Bisphenol A = DGEBA Curing system cross-linking Polyamines cured at room temperature
Curing by additive polymerisation no by-products Carboxyl acid anhydride cured at 100-180C
Complex reaction gives (small amounts) H2O as by-product but high temperature expels water.
Merkapto Low temperature, rapid curing
Exotherm HMS - allergies
MEK4540-2012-1.39
Vinylester
Chemical structure resembles epoxy, but cured as polyester
Prepolymer based on DGEBA + organic acid dissolved in styrene or other monomer
Also found as rubber-modified vinylester with high strain to failure.
MEK4540-2012-1.40
Properties of matrix materials
Tensile modulus [Gpa]
Tensile strength [MPa]
Density [g/cc]
Tmax [C]
Polyester 2-4 30 - 100 1.3 40-90
Vinylester 3.0-3.5 70 - 80 1.2 ~100
Epoxy 3-4 50 - 130 1.2
160
MEK4540-2012-1.41
Properties of fibre composites
MEK4540-2012-1.42
Properties of UD (uni-directional) composites
Following must be studied: Fibre content by both volume and weight Stiffness
E-modulus in both longitudinal and transverse directions G-modulus Poissons ratio
Strength tension, compression, shear various directions
MEK4540-2012-1.43
Nomenclature m matrix f fibre, reinforcement c composite 1 longitudinal direction 2 og 3 transverse direction 1,2,3 also denoted L,T,T
Laminate composite built up from several layers,
often with fibres in different directions UD ply layer with all fibres in same direction
Properties are different in transverse and longitudinal directions
UD composite all plies have same fibre direction Other possibilities:
Layers with fibres in 2 perpendicular directions (e.g. woven fabrics) cross-ply
Laminate with layers in several directions
laminate
ply
MEK4540-2012-1.44
UD composites: Volume and weight fractions Ratio between amounts of fibre and matrix can be described by use of
fibre volume fraction or fibre weight fraction
Has importance for mechanical properties
Volume fraction vc volume of composite vm volume of matrix vf volume of fibres Definition of volume fractions:
mfc vvv +=
c
mm
c
ff v
vV
vv
V ==
Weight fraction wc weight of composite wm weight of matrix wf weight of fibres Definition of weight fractions:
mfc www +=
c
mm
c
ff w
wW
ww
W ==
MEK4540-2012-1.45
Relationships between densities, volume and weight fractions
Relationship between densities c , f , m
=> =>
=> =>
Relationship between weight and volume fractions:
mfc www +=
mmffcc vvv +=
f
c
f
cc
ff
c
ff Vv
vww
W
===
m
c
mm VW
=
ct
cectvV
=
c
mm
c
ff v
vV
vv
V ==
c
mm
c
ff w
wW
ww
W ==
mmff
c
mm
c
ffc
VVvv
vv
+=
+=
m
m
f
f
c
c www
+=
mmff
m
cm
f
cf
c
WW
wwww
+=
+=1
We have also the void fraction
mfc vvv +=
MEK4540-2012-1.46
Strength and stiffness in longitudinal (fibre) direction Assumptions:
Fibres are uniform wrt. properties and diameter continuous and parallel through entire
composite Perfect adhesion between matrix and fibres. Pf, Pm, Pc are the respective forces Af, Am, Ac are the respective areas Respective strains are equal,
Then we have i.e.
=>
=> since
cmf ==
mfc PPP +=
mmffccc AAAP +==
c
mm
c
ffc A
AAA
+=
c
mm
c
ff A
AV
AA
V == mmffc VV +=
MEK4540-2012-1.47
Linear elastic case Differentiate wrt. strains:
contributions from fibres and matrix are proportional to volume fractions.
How much of the forces are taken up by the fibres?
mmffc VEVEE +=
c
c
m
m
f
f
EEE
==
( ) ( )fmmfmf
mmff
ff
c
f
VVEEEE
AAA
PP
+=
+=
cmf == =>
m
f
m
f
mm
ff
m
f
VV
EE
AA
PP
==
=>
c
f
c
f
m
f
m
f
EE
EE
==
=> and
and
m
mf
fc Vd
dV
dd
dd
+= =>
MEK4540-2012-1.48
Non-linear elastic case Generally a composite deforms according to linear theory. The deformation sequence is as follows:
1. Fibres and matrix undergo linear elastic deformation. Following still applies:
2. Fibres deform linearly while matrix enters a non-linear phase:
3. Both fibres and matrix deform non-linearly but following still applies:
4. Fibres fracture, resulting in fracture of the composite.
Several possible types of failure dependent on fibre fraction and fibre brittleness:
mmffc VEVEE +=
m
m
mffc Vd
dVEE
+=
mmffc VV +=
MEK4540-2012-1.49
To find Vmin we equate these, so that :
Strength and stiffness in longitudinal direction (contd.) Vmin = min. fibre volume fraction for composite
fracture to be determined by fibre fracture as opposed to matrix fracture
For : fibre fracture => composite
fracture because matrix cannot resist the load after fibres have failed. Then max. stress in composite is:
For : fibre fracture does not give composite fracture beause matrix can still resist the load. We assume the fibres do not carry forces when . Then max. stress in composite is:
minVV f >
minVV f f
( ) ( )fmffucu VVf
+= 1
( )( )
+
=
f
f
mmufu
mmuV
min
( )fmucu V= 1
*
MEK4540-2012-1.50
Strength and stiffness in longitudinal direction (contd.)
gives composite strength that is lower than matrix strength mu, while
can give either higher or lower.
More useful to define volume fraction Vcrit that gives lower strength limit mu : i.e. ( ) ( ) mufmffucu VV
f += 1
( )( )
=
f
f
mfu
mmuV
crit
minVV f < minVV f >
*
Recommended