textile structural composites yiping qiu college of textiles donghua university spring, 2006
TRANSCRIPT
Textile Structural Composites
Yiping Qiu
College of Textiles
Donghua University
Spring, 2006
Reading Assignment
Textbook chapter 1 General Information. High-Performance Composites: An Overview,
High-Performance Composites, 7-19, 2003 Sourcebook.
FRP Materials, Manufacturing Methods and Markets, Composites Technology, Vol. 6(3) 6-20, 2000.
Expectations At the conclusion of this section, you should be
able to: Describe the advantages and disadvantages of fiber
reinforced composite materials vs. other materials Describe the major applications of fiber reinforced
composites Classification of composites
Introduction What is a composite material?
Two or more phases with different properties
Why composite materials? Synergy
History Current Status
Introduction Applications
Automotive Marine Civil engineering Space, aircraft and military Sports
Applications in plane
Fiber reinforced composite materials
Classifications according to: Matrices
Polymer Thermoplastic Thermoset
Metal Ceramic Others
Fiber reinforced composite materials
Classifications Fibers
Length short fiber reinforced continuous fiber reinforced
Composition Single fiber type Hybrid
Mechanical properties Conventional Flexible
Fiber reinforced composite materials
Advantages High strength to weight ratio High stiffness to weight ratio High fatigue resistance No catastrophic failure Low thermal expansion in fiber oriented
directions Resistance to chemicals and environmental
factors
0
2
4
6
8S
pec
ific
gra
vity
(g
/cc)
Ste
el
Al a
lloy
Ti a
lloy
Car
bon/
epox
y
Kev
lar/
epox
y
materials
Comparison of specific gravities
0
200
400
600
800
1000
1200
1400
Te
ns
ile
str
en
gth
(M
Pa
)
Ste
el
Al a
lloy
Ti a
lloy
Ca
rbo
n/e
po
xy
Ke
vla
r/e
po
xy
Materials
Comparison of tensile strength
0
4
8
12
16M
od
ulu
s t
o w
eig
ht
rati
o (
109
m)
Ste
el
Al allo
y
Ti allo
y
Carb
on/e
poxy
Kevla
r/epoxy
Materials
Comparison of modulus to weight ratio
Fiber reinforced composite materials Disadvantages
Good properties in one direction and poor properties in other directions.
High cost due to expensive material and complicated fabrication processes.
Some are brittle, such as carbon fiber reinforced composites.
Not enough data for safety criteria.
Design of Composite Materials
Property Maps Merit index
Design of Composite Materials
Merit index Example for tensile stiffness of a beam
However, for a given tensile sample, tensile stiffness has nothing to do with length or L = 1 may be assumed
1 when
LA
W
AL
W
ALVW
W
FE
W
F
W
F
A
FE
Design of Composite Materials
How about for torsion beams and bending plates? Lets make the derivation of these our first homework.
Major components for fiber-reinforced composites Reading assignment:
Textbook Chapter 2 Fibers and matrices Fibers
Share major portion of the load Matrix
To transfer stress between the fibers To provide a barrier against an adverse environment To protect the surface of the fibers from mechanical
abrasion
Major components for fiber reinforced composites
Coupling agents and coatings to improve the adhesion between the fiber and the matrix to protect fiber from being reacted with the matrix or other
environmental conditions such as water moisture and reactive fluids.
Fillers and other additives: to reduce the cost, to increase stiffness, to reduce shrinkage, to control viscosity, to produce smoother surface.
Materials for fiber reinforced composites
Mainly two components: Fibers Matrices
Materials for fiber reinforced composites
Fibers Influences:
Specific gravity, Tensile and compressive strength and
modulus, Fatigue properties, Electrical and thermal properties, Cost.
Materials for fiber reinforced composites
Fibers Fibers used in composites
Polymeric fibers such as PE (Spectra 900, 1000) PPTA: Poly(para-phenylene terephthalamide)
(Kevlar 29, 49, 149, 981, Twaron) Polyester (Vectran or Vectra) PBZT: Poly(p-phenylene benzobisthiozol)
Materials for fiber reinforced composites
Fibers Inorganic fibers:
Glass fibers: S-glass and E-glass Carbon or graphite fibers: from PAN and Pitch Ceramic fibers: Boron, SiC, Al2O3
Metal fibers: steel, alloys of W, Ti, Ni, Mo etc. (high melting temperature metal fibers)
Materials for fiber reinforced composites
Most frequently used fibers Glass Carbon/graphite PPTA (Kevlar, etc.) Polyethylene (Spectra) Polyester (Vectra)
Materials for fiber reinforced composites
Carbon fibers Manufacturing processes Structure and properties
Materials for fiber reinforced composites
Carbon fibers Manufacturing processes
Thermal decomposition of fibrous organic precursors: PAN and Rayon Extrusion of pitch fibers
Materials for fiber reinforced composites
Carbon fiber manufacturing processes Thermal decomposition of fibrous organic
precursors Rayon fibers
Rayon based carbon fibers Stabilization at 400°C in O2, depolymerization &
aromatization Carbonization at 400-700°C in an inert atmosphere Stretch and graphitization at 700-2800°C (improve orientation
and increase crystallinity by 30-50%)
Materials for fiber reinforced composites
Carbon fiber manufacturing processes Thermal decomposition of fibrous organic
precursors PAN (polyarylonitrile) based carbon fibers
PAN fibers (CH2-CH(CN)) Stabilization at 200-300°C in O2, depolymerization &
aromatization, converting thermoplastic PAN to a nonplastic cyclic or ladder compound (CN groups combined and CH2 groups oxidized)
Carbonization at 1000-1500°C in an inert atmosphere to get rid of noncarbon elements (O and N) but the molecular orientation is still poor.
Stretch and graphitization at >1800°C, formation of turbostratic structure
Materials for fiber reinforced composites
Pitch based carbon fibers pitch - high molecular weight byproduct
of distillation of petroleum heated >350°C, condensation reaction,
formation of mesophase (LC) melt spinning into pitch fibers conversion into graphite fibers at ~2000°C
Materials for fiber reinforced composites
Carbon fibers Advantages
High strength Higher modulus Nonreactive
Resistance to corrosion High heat resistance high tensile strength at elevated temperature
Low density
Materials for fiber reinforced composites
Carbon fibers Disadvantages
High cost Brittle
Materials for fiber reinforced composites
Carbon fibers Other interesting properties
Lubricating properties Electrical conductivity Thermal conductivity Low to negative thermal expansion coefficient
Materials for fiber reinforced composites
Carbon fibers heat treatment below 1700°C
less crystalline and lower modulus (<365 GPa)
Graphite fibers heat treatment above 1700°C
More crystalline (~80%) and higher modulus (>365GPa)
Materials for fiber reinforced composites
Glass fibers Compositions and properties Advantages and disadvantages
Materials for fiber reinforced composites
Glass fibers Compositions and Structures
Mainly SiO2 +oxides of Ca, B, Na, Fe, Al Highly cross-linked polymer
Noncrystaline No orientation
Si and O form tetrahedra with Si centered and O at the corners forming a rigid network
Addition of Ca, Na, & K with low valency breaks up the network by forming ionic bonds with O strength and modulus
Microscopic view of glass fiber
Cross polar First order red plate
Materials for fiber reinforced composites
Glass fibers Types and Properties
E-glass (for electric) draws well good strength & stiffness good electrical and weathering properties
Materials for fiber reinforced composites
Glass fibers Types and Properties
C-glass (for corrosion) good resistance to corrosion low strength
Materials for fiber reinforced composites
Glass fibers Types and Properties
S-glass (for strength) high strength & modulus high temperature resistance more expensive than E
Materials for fiber reinforced composites
Properties of Glass fibers
fibers Tensilestrength(MPa)
TensileModulus(GPa)
Coeff. OfThermalExpension10-6/K
DielectricConst. (a)
E-glass 3450 72.5 5.0 6.3
S-glass 4590 86.0 5.6 5.1
Materials for fiber reinforced composites
Glass fibers Production
Melt spinning
Materials for fiber reinforced composites Glass fibers
sizing: purposes
protest surface bond fibers together anti-static improve interfacial bonding
Necessary constituents a film-forming polymer to provide protecting
e.g. polyvinyl acetate a lubricant a coupling agent: e.g. organosilane
Materials for fiber reinforced composites
Glass fibers Advantages
high strength same strength and modulus in transverse direction
as in longitudinal direction low cost
Materials for fiber reinforced composites
Glass fibers disadvantages
relatively low modulus high specific density (2.62 g/cc) moisture sensitive
Materials for fiber reinforced composites
Kevlar fibers Structure
Polyamide with benzene rings between amide groups
Liquid crystalline Planar array and pleated system
Materials for fiber reinforced composites
Kevlar fibers Types
Kevlar 29, E = 50 GPa Kevlar 49, E = 125 GPa Kevlar 149, E = 185 GPa
Materials for fiber reinforced composites
Kevlar fibers Advantages
high strength & modulus low specific density (1.47g/cc) relatively high temperature resistance
Materials for fiber reinforced composites
Kevlar fibers Disadvantages
Easy to fibrillate poor transverse properties susceptible to abrasion
Materials for fiber reinforced composites
Spectra fibers
Structure: (CH2CH2)n Linear polymer - easy to pack No reactive groups
Advantages high strength and modulus low specific gravity excellent resistance to chemicals nontoxic for biomedical
applications
Materials for fiber reinforced composites
Spectra fibers Disadvantages
poor adhesion to matrix high creep low melting temperature
Materials for fiber reinforced composites
Other fibers SiC and Boron
Production Chemical Vapor Deposition (CVD)
Monofilament Carbon or Tungsten core heated by passing an
electrical current Gaseous carbon containing silane
Materials for fiber reinforced composites
SiC Production
Polycarbosilane (PCS) Multi-filaments polymerization process to produce precursor PCS pyrolised at 1300ºC
Whiskers Small defect free single crystal
Materials for fiber reinforced composites
Particulate small aspect ratio high strength and modulus mostly cheap
Materials for fiber reinforced composites
The strength of reinforcements Compressive strength Fiber fracture and flexibility Statistical treatment of fiber strength
Materials for fiber reinforced composites
The strength of reinforcements Compressive strength
(Mainly) Euler Buckling
22
* 16
L
dEb
2L
EIcP
Materials for fiber reinforced composites
The strength of reinforcements Factors determining compressive strength
Matrix material Fiber diameter or aspect ratio (L/d) fiber properties
carbon & glass >> Kevlar
Materials for fiber reinforced composites
The strength of reinforcements Fiber fracture
Mostly brittle e.g. Carbon, glass, SiC
Some ductile e.g. Kevlar, Spectra
Fibrillation e.g. Kevlar
Materials for fiber reinforced composites
The strength of reinforcements Fiber flexibility
How easy to be bent Moment required to bend a round fiber:
64
4dEEIM
E = Young’s Modulus
d = fiber diameter
= curvature
Materials for fiber reinforced composites
The strength of reinforcements Fiber failure in bending
Stress on surface Tensile stress:
2
dE
E = Young’s Modulus
d = fiber diameter
= curvature
Materials for fiber reinforced composites
The strength of reinforcements Fiber failure in bending
Stress on surface Maximum curvature
Ed*
max
2
* = fiber tensile strength
Materials for fiber reinforced composites
The strength of reinforcements Fiber failure in bending
When bent, many fibers fail in compressionKevlar forms kink bands
Materials for fiber reinforced composites
Statistical treatment of fiber strength Brittle materials: failure caused by random
flaw don’t have a well defined tensile strength presence of a flaw population
Statistical treatment of fiber strengthPeirce (1928): divide a fiber into incremental
lengths
NLLLLL 321
Materials for fiber reinforced composites
Statistical treatment of fiber strength Peirce’s experiment
Hypothesis: The longer the fiber length, the higher the probability
that it will contain a serious flaw. Longer fibers have lower mean tensile strength. Longer fibers have smaller variation in tensile strength.
Materials for fiber reinforced composites
Statistical treatment of fiber strength Peirce’s experiment
Experimental verification:
variationoft Coefficien
oflength a fiber with ofStrength
oflength a fiber with ofStrength
)1(2.41/ 5/1
CV
l
nl
CVn
l
nl
lnl
Materials for fiber reinforced composites
Statistical treatment of fiber strength Weakest Link Theory (WLT)
define n = No. of flaws per unit length causing failure under stress .
For the first element, the probability of failure
11 LnPf
The probability for the fiber to survive
)1()1)(1( 21 fNffs PPPP
Materials for fiber reinforced composites
Statistical treatment of fiber strength Weakest Link Theory (WLT)
If the length of each segment is very small, then Pfi are all very small, Therefore (1-Pfi) exp(-Pfi)
The probability for the fiber to survive
)](exp[ 21 fNffs PPPP
)exp()](exp[ 21 LnLnLnLn N
Materials for fiber reinforced composites
Statistical treatment of fiber strength Weibull distribution of fiber strength
Weibull’s assumption:
m
nL
00
m = Weibull shape parameter (modulus).
0 = Weibull scale parameter, characteristic
strength.
L0 = Arbitrary reference length.
Materials for fiber reinforced composites
Statistical treatment of fiber strength Weibull distribution of fiber strength
Thus
m
f L
LP
00
exp1
Materials for fiber reinforced composites
Statistical treatment of fiber strength Weibull distribution of fiber strength
Discussion: Shape parameter ranges 2-20 for ceramic and many
other fibers. The higher the shape parameter, the smaller the
variation. When <0, the probability of failure is small if m is
large. When 0, failure occurs. Weibull distribution is used in bundle theory to predict
fiber bundle and composite strength.
Materials for fiber reinforced composites
Statistical treatment of fiber strength Weibull distribution of fiber strength
Plot of fiber strength or failure strain data let m
s L
LP
00
)ln(
m
s L
L
P
00
1ln
00 lnlnlnln1
lnln mmLLPs
Statistical treatment of fiber strength
Example Estimate number of fibers fail at a gage
length twice as much as the gage length in single fiber test
L/L0 = 2
Matrices
Additional reading assignment: Jones, F.R., Handbook of Polymer-
Fiber Composites, sections: 2.4-2.6, 2.9, 2.10, 2.12.
Matrices
Polymer Metal Ceramic
Matrices
Polymer Thermosetting resins
Epoxy Unsatulated polyester Vinyl ester high temperature:
Polyimides Phenolic resins
Matrices
Properties minimum desired Typicalepoxy
Tensile strength(MPa)
70 >100 ---
Modulus (GPa) 2.0 >3.0 3.8
Ultimate Strain(%)
5 >10 1 - 2
Glass transitiontemperature (C)
121 >177 121
PolymerTarget net resin properties
Epoxy resins
Starting materials: Low molecular weight organic compounds
containing epoxide groups
Epoxy Resins
Types of epoxy resins
Epoxy resins
Types of epoxy resin bifuctional: diglycidyl ether of bisphenol A
a distribution of monomers n is fractional: effect of n
molecular weight viscosity curing temp. distance between crosslinks Tg & ductility -OH moisture absorption
Epoxy resins
Types of epoxy resin (cont.) Trifunctional (glycidyl amines) Tetrafunctional
higher functionality potentially higher crosslink densities higher Tg Less -OH groups moisture absorption
Epoxy resins Curing
Copolymerization: A hardener required: e.g. DDS, DICY Hardeners have two active “H” atoms to add to the
epoxy groups of neighboring epoxy molecules, usually from -NH2
Formation of -OH groups: moisture sensitive Addition polymerization: No small molecules formed
no volatile formation Stoichiometric concentration used, phr: part per hundred
(parts) of resin
Epoxy resin Major ingredients: epoxy resin and curing
agent
Epoxy resin Chemical reactions
Epoxy resin Chemical reactions
Epoxy resins Curing
Homopolymerization: Addition polymerization: a catalyst or initiator required:
eg. Tertiary amines and BF3 compounds Less -OH groups formed Typical properties of addition polymers
Combination of catalyst with hardeners
Epoxy Resins Reaction of homopolymerization
Epoxy resins
Epoxy resins Mechanical and thermomechanical properties
Effect of curing agent on mechanical properties Heat distortion temperature (HDT)
measured as temperature at which deflection of 0.25 mm of 100 mm long bar under 0.455 MPa fiber stress occurs.
related but Tg
Moisture absorption: 1% decrease Tg by 20ºK
Polyimides Largest class of high temperature polymers in
composites Types
PMR (polymerization of monomeric reactants) polyimides are insoluble and infusible. in situ condensation polymerization of monomers in a solvent 2 stage process:
first stage to form imidized prepolymer of oligomer and volatile by-products removed using autoclave or vacuum oven.
Second stage: prepolymer is crosslinked via reaction of the norbornene end cap under high pressure and temperature (316ºC and 200 psi)
Polyimides
Types bis-imides (derived from monomers with 2
preformed imide groups). Typical BMI (bismaleimides) Used for lower temperature range ~ 200ºC
Polyimides Properties (show tables)
Polyimides
Advantages: Heat resistant
Drawbacks: toxicity of constituent chemicals (e.g. MDA) microcracking of fibers on thermal cycling high processing temperature
Typical ApplicationsEngine parts in aerospace industry
Phenolic resins Prepared through condensation
polymerization between phenol and formaldehyde.
Large quantity of Water generated (up to 25%) leading to high void content
Phenolic resins Advantages:
High temperature stability Chemical resistance Flame retardant Good electrical properties
Typical applications Offshore structures Civil engineering Marine Auto parts: water pumps, brake components pan handles and electric meter cases
Time-temperature-transformation diagrams for thermosets resins
Additional reading assignment: reserved: Gillham, J.K., Formation and
Properties of Thermosetting and High Tg Polymeric Materials, Polymer Engineering and Science, 26, 1986, p1429-1431
Time-temperature-transformation diagrams for thermosets resins
Time-temperature-transformation diagrams for thermosets resins
Important concepts Gelation
formation of an infinite network sol and gel coexist
Vitrification Tg rises to isothermal temperature of cure Tcure > Tg, rubbery material Tcure < Tg, glassy material After vitrification, conversion of monomer
almost ceases.
Time-temperature-transformation diagrams for thermosets resins
Important concepts Devitrification
Tg decreases through isothermal temperature of cure due to degradation
degradation leads to decrosslink and formation of plasticizing materials
Char or vitrification due to increase of crosslink and volatilization of
low molecular weight plasticizing materials
Time-temperature-transformation diagrams for thermosets resins
Important concepts Three critical temperatures:
Tg - Tg of cured system gelTg - Tg of gel Tgo - Tg of reactants
Time-temperature-transformation diagrams for thermosets resins
Discussion Ungelled glassy state is good for
commercial molding compounds Tgo > Tprocessing, processed as solid Tgo < Tprocessing, processed as liquid
Store temperature < gelTg to avoid gelation Resin fully cured when Tg = Tg Tg > Tcure about 40ºC Full cure is achieved most readily by cure at
T > Tg and slowly at T < Tg.
Unsaturated polyester Reading assignment Mallick, P.K., Fiber Reinforced Composites .
Materials, Manufacturing and Design, pp56-64. Resin:
Products of condensation polymerization of diacids and diols e.g. Maleic anhydride and ethylene glycol
Strictly alternating polymers of the type A-B-A-B-A-B At least one of the monomers is ethylenically
unsaturated
Unsaturated polyester
Unsaturated polyester
Unsaturated polyester Cross-linking agent
Reactive solvent of the resin: e.g. styrene Addition polymerization with the resin molecules:
initiator needed, e.g. peroxide Application of heat to decompose the initiator to start
addition polymerization an accelerator may be added to increase the
decomposition rate of the initiator.
Unsaturated polyester
Unsaturated polyester Factors to control
properties Cross-linking density:
addition of saturated diacids as part of the monomer for the resin: e.g phthalic anhydrid, isophthalic acid and terephthalic acid
as ratio of saturated acids to unsaturated acids increases, strength and elongation increase while HDT decreases
Unsaturated polyester Factors controlling properties
Type of acids Terephthalic acids provide higher HDT than the other two acids
due to better packing of molecules nonaromatic acid: adipic acid HOOC(CH2)4COOH, lowers
stiffness
Resin microstructure: local extremely high density of cross-links.
Type of diols larger diol monomer: diethylene glycol bulky side groups
Unsaturated polyester Factors to control
properties Type of crosslinking agent
amount of styrene: more styrene increases the distance of the space of neighboring polyester molecules lower modulus
Excessive styrene: self-polymerization formation of polystyrene polystyrene-like properties
Unsaturated polyester Advantages
Low viscosity Fast cure Low cost
Disadvantages lower properties than epoxy large mold shrinkage sink marks
an incompatible thermoplastic mixed into the resin to form a dispersed phase in the resin “low profile” system
Vinyl ester Resin:
Products of addition polymerization of epoxy resin and an unsaturated carboxylic acid (vinyl)
unsaturated C=C bonds are at the end of a vinyl ester molecule fewer cross-links more flexible
Cross-linking agent The polymer is dissolved in styrene Addition polymerization to form cross-links Formation of a gigantic molecule Similar curing reaction as unsaturated polyester resin
Vinyl ester
Vinyl ester
Vinyl ester Advantages
epoxy-like: excellent chemical resistance high tensile strength
polyester-like: Low viscosity Fast curing less expensive
good adhesion to glass fibers due to existence of -OH Disadvantages:
Large volumetric shrinkage (5 – 10 %)
Vinyl ester
Advantages of thermosetting resins
High strength and modulus. Less creep and stress relaxation Good resistance to heat and chemicals Better wet-out between fibers and matrix due to
low viscosity before cross-linking
Disadvantages of thermosetting resins
Limited storage life Long time to cure Low strain to failure Low impact resistance Large shrinkage on curing
Thermoplastic matrices
Reading assignment: Mallick, P.K., Fiber Reinforced Composites .
Materials, Manufacturing and Design, section 2.4 pp 64-69.
Types: Conventional: no chemical reaction during processing
Semi-crystalline Liquid crystal Amorphous
Pseudothermoplastics: molecular weight increase and expelling volatiles
Thermoplastic matrices
examples: Conventional
Nylon Polyethylene Polypropylene Polycarbonate Polyester PMMA
Thermoplastic matrices examples:
Advanced (e.g.)
Thermoplastic matrices examples:
Advanced (e.g.) Polyimide
Thermoplastic matrices
Thermoplastic matrices
Main descriptors: Linear Repeatedly meltable
Properties and advantages of thermoplastic matrices
High failure strain High impact resistance Unlimited storage life at room temperature Short fabrication time Postformability (thermoforming) Ease of repair by welding, solvent bonding Ease of handling (no tackiness)
Thermoplastic matrices
Disadvantages of thermoplastic matrices
High melt or solution viscosity (high MW) Difficult to mix them with fibers Relatively low creep resistance Low heat resistance for conventional
thermoplastics
Metal Matrices
Examples Al, Ti, Mg, Cu and Super alloys
Reinforcements: Fibers: boron, carbon, metal wires Whiskers Particulate
Metal Matrices
Fiber matrix interaction Fiber and matrix mutually nonreactive and
insoluble Fiber and matrix mutually nonreactive but soluble Fiber and matrix react to form compounds at
interface
Metal Matrices
Advantage of metal matrix composites (MMC) Versus unreinforced metals
higher strength to density ratio better properties at elevated temperature lower coefficient of thermal expansion better wear characteristics better creep performance
Metal Matrices
Advantage of MMC Versus polymeric matrix
better properties at elevated temperature higher transverse stiffness and strength moisture insensitivity higher electrical and thermal conductivity better radiation resistance less outgassing contamination
Metal Matrices
Disadvantage of MMC higher cost
high processing temperature relatively immature technology complex and expensive fabrication methods with
continuous fiber reinforcements
high specific gravity compared with polymer corrosion at fiber matrix interface (high affiliation
to oxygen) limited service experience
Ceramic Matrices
Glass ceramics glass forming oxides, e.g. Borosilicates and
aluminosilicates semi-crystalline with lower softening temperature
Conventional ceramicsSiC, Si3N4, Al2O3, ZrO2
fully crystalline Cement and concrete Carbon/carbon
Ceramic Matrices
Increased toughness through deflected crack propagation on fiber/matrix interface.
Example: Carbon/carbon composites