Textile Structural Composites - libvolume8.xyzlibvolume8.xyz/textile/btech/semester4/textile... ·...

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


• Classifications

� Fibers

� Length

� short fiber reinforced

� continuous fiber reinforced

� Composition

� Single fiber type

� Hybrid

�Mechanical properties

� Conventional

� Flexible


� 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

8 Specific gravity

(g/cc)

Steel

Al alloy

Ti alloy

Carbon/epoxy

Kevlar/epoxy

materials

Comparison of specific gravities

0

200

400

600

800

1000

1200

1400

Tensile strength (MPa)

Steel

Al alloy

Ti alloy

Carbon/epoxy

Kevlar/epoxy

Materials

Comparison of tensile strength

0

4

8

12

16Modulus to weight

ratio (109m)

Steel

Al alloy

Ti alloy

Carbon/epoxy

Kevlar/epoxy

Materials

Comparison of modulus to

weight ratio


� 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


� 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

ρ

ρρ

( )

ερ

ερ

ερεεσ

W

FE

W

F

W

F

A

FE

=∴

====Q


� 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


� Fibers � Influences:

• Specific gravity,

• Tensile and compressive strength and

modulus,

• Fatigue properties,

• Electrical and thermal properties,

• Cost.


� 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)


� 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)


� Most frequently used fibers

� Glass

� Carbon/graphite

� PPTA (Kevlar, etc.)

� Polyethylene (Spectra)

� Polyester (Vectra)


� Carbon fibers

� Manufacturing processes

� Structure and properties


� Carbon fibers

� Manufacturing processes

� Thermal decomposition of fibrous organic

precursors:

� PAN and Rayon

� Extrusion of pitch fibers


� 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%)


� 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


� 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


� Carbon fibers

� Advantages

� High strength

� Higher modulus

� Nonreactive

� Resistance to corrosion

� High heat resistance

� high tensile strength at elevated temperature

� Low density


� Carbon fibers

� Disadvantages

� High cost

� Brittle


� Carbon fibers

� Other interesting properties

� Lubricating properties

� Electrical conductivity

� Thermal conductivity

� Low to negative thermal expansion coefficient


� 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)


� Glass fibers

� Compositions and properties

� Advantages and disadvantages


� 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


� Glass fibers

� Types and Properties

� E-glass (for electric)

� draws well

� good strength & stiffness

� good electrical and weathering properties


� Glass fibers


� C-glass (for corrosion)

� good resistance to corrosion

� low strength


� Glass fibers


� S-glass (for strength)

� high strength & modulus

� high temperature resistance

� more expensive than E


� Properties of Glass fibers

f i b e r s T e n s i l e

s t r e n g t h

( M P a )

T e n s i l e

M o d u l u s

( G P a )

C o e f f . O f

T h e r m a l

E x p e n s i o n1 0 - 6 / K

D ie le c t r i c

C o n s t . ( a )

E - g l a s s 3 4 5 0 7 2 . 5 5 . 0 6 . 3

S - g l a s s 4 5 9 0 8 6 . 0 5 . 6 5 . 1


� Glass fibers

� Production

�Melt spinning


� 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


� Glass fibers

� Advantages

� high strength

� same strength and modulus in transverse direction

as in longitudinal direction

� low cost


� Glass fibers

� disadvantages

� relatively low modulus

� high specific density (2.62 g/cc)

�moisture sensitive


� Kevlar fibers

� Structure

� Polyamide with benzene rings between amide

groups

� Liquid crystalline

� Planar array and pleated system


� Kevlar fibers

� Types

� Kevlar 29, E = 50 GPa




� Kevlar fibers

� Advantages

� high strength & modulus

� low specific density (1.47g/cc)

� relatively high temperature resistance


� Kevlar fibers

� Disadvantages

� Easy to fibrillate

� poor transverse properties

� susceptible to abrasion


� 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


� Spectra fibers

� Disadvantages

� poor adhesion to matrix

� high creep

� low melting temperature


� 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


� SiC

� Production

� Polycarbosilane (PCS)

� Multi-filaments

� polymerization process to produce precursor

� PCS pyrolised at 1300ºC

� Whiskers

� Small defect free single crystal


� Particulate

� small aspect ratio

� high strength and modulus

� mostly cheap


� The strength of reinforcements

� Compressive strength

� Fiber fracture and flexibility

� Statistical treatment of fiber strength



� Compressive strength

� (Mainly) Euler Buckling

22

*16

=L

dEb

πσ

2L

EIcP =



� Factors determining compressive strength

�Matrix material

� Fiber diameter or aspect ratio (L/d)

� fiber properties

� carbon & glass >> Kevlar



� Fiber fracture

�Mostly brittle

� e.g. Carbon, glass, SiC

� Some ductile

� e.g. Kevlar, Spectra

� Fibrillation

� e.g. Kevlar



� Fiber flexibility

�How easy to be bent

� Moment required to bend a round fiber:

κπ

κ64

4dEEIM ==

E = Young’s Modulus

d = fiber diameter

κ = curvature



� Fiber failure in bending

�Stress on surface

� Tensile stress:

2

dEκσ =

E = Young’s Modulus

d = fiber diameter

κ = curvature




�Stress on surface

� Maximum curvature

Ed

*max

2σκ =

σ* = fiber tensile strength




�When bent, many fibers fail in compression

�Kevlar forms kink bands



� Brittle materials: failure caused by random

flaw

�don’t have a well defined tensile strength

�presence of a flaw population


�Peirce (1928): divide a fiber into incremental

lengths

NLLLLL ∆++∆+∆+∆= L321



� 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.



� 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

σ

σ

σσ



� Weakest Link Theory (WLT)

�define nσ = No. of flaws per unit length causing

failure under stress σ. �For the first element, the probability of failure

11 LnPf ∆= σ

The probability for the fiber to survive

)1()1)(1( 21 fNffs PPPP −−−= L



� 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 +++−= L

)exp()](exp[21 σσσσ LnLnLnLn

N−=∆++∆+∆−= L



� Weibull distribution of fiber strength

�Weibull’s assumption:

m

nL

=

0

0

σσ

σ

m = Weibull shape parameter (modulus).

σ0 = Weibull scale parameter, characteristic strength.

L0 = Arbitrary reference length.




�Thus

−−=

m

fL

LP

00

exp1σσ




�Discussion: � Shape parameter ranges 2-20 for ceramic and many other fibers.

� The higher the shape parameter, the smaller the variation.

� When σ <σ0, the probability of failure is small if m is large.

� When σ ≥σ0, failure occurs. � Weibull distribution is used in bundle theory to predict fiber bundle and composite strength.




� Plot of fiber strength or failure strain data

� let

m

sL

LP

−=

00

)ln(σσ

m

s L

L

P

=

00

1ln

σσ

( ) ( ) ( ) ( )00 lnlnlnln1

lnln σσ 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 transition

temperature (°C)121 >177 121

Polymer

Target 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 Applications

�Engine 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





� 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.




� 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




� Three critical temperatures:

� Tg∞ - Tg of cured system

� gelTg - Tg of gel

� Tgo - Tg of reactants



� 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




� 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 � 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


� 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


� 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


� examples:

� Conventional

� Nylon

� Polyethylene

� Polypropylene

� Polycarbonate

� Polyester

� PMMA


� examples:

� Advanced (e.g.)


� examples:

� Advanced (e.g.)

� Polyimide



� 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)


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 ceramics

�SiC, 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

Date post:	26-Mar-2020
Category:	Documents
Upload:	others
View:	7 times
Download:	1 times

Textile Structural Composites - libvolume8.xyzlibvolume8.xyz/textile/btech/semester4/textile... ·...

Documents