Textile Structural Composites

1
Textile Structural Composites

• Yiping Qiu
• College of Textiles
• Donghua University
• Spring, 2006

2
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.

3
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

4
Introduction

• What is a composite material?
• Two or more phases with different properties
• Why composite materials?
• Synergy
• History
• Current Status

5
Introduction

• Applications
• Automotive
• Marine
• Civil engineering
• Space, aircraft and military
• Sports

6
Applications in plane
7
Fiber reinforced composite materials

• Classifications according to
• Matrices
• Polymer
• Thermoplastic
• Thermoset
• Metal
• Ceramic
• Others

8
Fiber reinforced composite materials

• Classifications
• Fibers
• Length
• short fiber reinforced
• continuous fiber reinforced
• Composition
• Single fiber type
• Hybrid
• Mechanical properties
• Conventional
• Flexible

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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

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Comparison of specific gravities
8
6
Specific gravity
(g/cc)
4
2
0
Steel
Al alloy
Ti alloy
Kevlar/epoxy
Carbon/epoxy
materials
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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.

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Design of Composite Materials

• Property Maps
• Merit index

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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

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Design of Composite Materials

• How about for torsion beams and bending plates?
  Lets make the derivation of these our first
  homework.

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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

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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.

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Materials for fiber reinforced composites

• Mainly two components
• Fibers
• Matrices

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Materials for fiber reinforced composites

• Fibers
• Influences
• Specific gravity,
• Tensile and compressive strength and modulus,
• Fatigue properties,
• Electrical and thermal properties,
• Cost.

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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)

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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)

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Materials for fiber reinforced composites

• Most frequently used fibers
• Glass
• Carbon/graphite
• PPTA (Kevlar, etc.)
• Polyethylene (Spectra)
• Polyester (Vectra)

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Materials for fiber reinforced composites

• Carbon fibers
• Manufacturing processes
• Structure and properties

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Materials for fiber reinforced composites

• Carbon fibers
• Manufacturing processes
• Thermal decomposition of fibrous organic
  precursors
• PAN and Rayon
• Extrusion of pitch fibers

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Materials for fiber reinforced composites

• Carbon fiber manufacturing processes
• Thermal decomposition of fibrous organic
  precursors
• Rayon fibers
• Rayon based carbon fibers
• Stabilization at 400C in O2, depolymerization
  aromatization
• Carbonization at 400-700C in an inert atmosphere
• Stretch and graphitization at 700-2800C (improve
  orientation and increase crystallinity by 30-50)

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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 200-300C in O2,
  depolymerization aromatization, converting
  thermoplastic PAN to a nonplastic cyclic or
  ladder compound (CN groups combined and CH2
  groups oxidized)
• Carbonization at 1000-1500C in an inert
  atmosphere to get rid of noncarbon elements (O
  and N) but the molecular orientation is still
  poor.
• Stretch and graphitization at gt1800C, formation
  of turbostratic structure

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Materials for fiber reinforced composites

• Pitch based carbon fibers
• pitch - high molecular weight byproduct of
  distillation of petroleum
• heated gt350C, condensation reaction, formation
  of mesophase (LC)
• melt spinning into pitch fibers
• conversion into graphite fibers at 2000C

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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

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Materials for fiber reinforced composites

• Carbon fibers
• Disadvantages
• High cost
• Brittle

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Materials for fiber reinforced composites

• Carbon fibers
• Other interesting properties
• Lubricating properties
• Electrical conductivity
• Thermal conductivity
• Low to negative thermal expansion coefficient

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Materials for fiber reinforced composites

• Carbon fibers
• heat treatment below 1700C
• less crystalline
• and lower modulus (lt365 GPa)
• Graphite fibers
• heat treatment above 1700C
• More crystalline (80) and
• higher modulus (gt365GPa)

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Materials for fiber reinforced composites

• Glass fibers
• Compositions and properties
• Advantages and disadvantages

34
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

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Microscopic view of glass fiber
Cross polar
First order red plate
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Materials for fiber reinforced composites

• Glass fibers
• Types and Properties
• E-glass (for electric)
• draws well
• good strength stiffness
• good electrical and weathering properties

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Materials for fiber reinforced composites

• Glass fibers
• Types and Properties
• C-glass (for corrosion)
• good resistance to corrosion
• low strength

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Materials for fiber reinforced composites

• Glass fibers
• Types and Properties
• S-glass (for strength)
• high strength modulus
• high temperature resistance
• more expensive than E

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Materials for fiber reinforced composites

• Properties of Glass fibers

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Materials for fiber reinforced composites

• Glass fibers
• Production
• Melt spinning

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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

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Materials for fiber reinforced composites

• Glass fibers
• Advantages
• high strength
• same strength and modulus in transverse direction
  as in longitudinal direction
• low cost

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Materials for fiber reinforced composites

• Glass fibers
• disadvantages
• relatively low modulus
• high specific density (2.62 g/cc)
• moisture sensitive

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Materials for fiber reinforced composites

• Kevlar fibers
• Structure
• Polyamide with benzene rings between amide groups
• Liquid crystalline
• Planar array and pleated system

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Materials for fiber reinforced composites

• Kevlar fibers
• Types
• Kevlar 29, E 50 GPa
• Kevlar 49, E 125 GPa
• Kevlar 149, E 185 GPa

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Materials for fiber reinforced composites

• Kevlar fibers
• Advantages
• high strength modulus
• low specific density (1.47g/cc)
• relatively high temperature resistance

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Materials for fiber reinforced composites

• Kevlar fibers
• Disadvantages
• Easy to fibrillate
• poor transverse properties
• susceptible to abrasion

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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

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Materials for fiber reinforced composites

• Spectra fibers
• Disadvantages
• poor adhesion to matrix
• high creep
• low melting temperature

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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

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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

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Materials for fiber reinforced composites

• Particulate
• small aspect ratio
• high strength and modulus
• mostly cheap

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Materials for fiber reinforced composites

• The strength of reinforcements
• Compressive strength
• Fiber fracture and flexibility
• Statistical treatment of fiber strength

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Materials for fiber reinforced composites

• The strength of reinforcements
• Compressive strength
• (Mainly) Euler Buckling

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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 gtgt Kevlar

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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

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Materials for fiber reinforced composites

• The strength of reinforcements
• Fiber flexibility
• How easy to be bent
• Moment required to bend a round fiber

E Youngs Modulus d fiber diameter ?
curvature
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Materials for fiber reinforced composites

• The strength of reinforcements
• Fiber failure in bending
• Stress on surface
• Tensile stress

E Youngs Modulus d fiber diameter ?
curvature
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Materials for fiber reinforced composites

• The strength of reinforcements
• Fiber failure in bending
• Stress on surface
• Maximum curvature

? fiber tensile strength
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Materials for fiber reinforced composites

• The strength of reinforcements
• Fiber failure in bending
• When bent, many fibers fail in compression
• Kevlar forms kink bands

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Materials for fiber reinforced composites

• Statistical treatment of fiber strength
• Brittle materials failure caused by random flaw
• dont have a well defined tensile strength
• presence of a flaw population
• Statistical treatment of fiber strength
• Peirce (1928) divide a fiber into incremental
  lengths

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Materials for fiber reinforced composites

• Statistical treatment of fiber strength
• Peirces 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.

63
Materials for fiber reinforced composites

• Statistical treatment of fiber strength
• Peirces experiment
• Experimental verification

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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

The probability for the fiber to survive
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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

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Materials for fiber reinforced composites

• Statistical treatment of fiber strength
• Weibull distribution of fiber strength
• Weibulls assumption

m Weibull shape parameter (modulus). ?0
Weibull scale parameter, characteristic
strength. L0 Arbitrary reference length.
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Materials for fiber reinforced composites

• Statistical treatment of fiber strength
• Weibull distribution of fiber strength
• Thus

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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 ? lt?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.

69
Materials for fiber reinforced composites

• Statistical treatment of fiber strength
• Weibull distribution of fiber strength
• Plot of fiber strength or failure strain data
• let

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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

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Matrices

• Additional reading assignment
• Jones, F.R., Handbook of Polymer-Fiber
  Composites, sections
• 2.4-2.6, 2.9, 2.10, 2.12.

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Matrices

• Polymer
• Metal
• Ceramic

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Matrices

• Polymer
• Thermosetting resins
• Epoxy
• Unsatulated polyester
• Vinyl ester
• high temperature
• Polyimides
• Phenolic resins

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Matrices
Polymer Target net resin properties
75
Epoxy resins

• Starting materials
• Low molecular weight organic compounds containing
  epoxide groups

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Epoxy Resins

• Types of epoxy resins

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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

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Epoxy resins

• Types of epoxy resin (cont.)
• Trifunctional (glycidyl amines)
• Tetrafunctional
• higher functionality
• potentially higher crosslink densities
• higher Tg
• Less -OH groups ? ? moisture absorption

79
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

80
Epoxy resin

• Major ingredients epoxy resin and curing agent

81
Epoxy resin

• Chemical reactions

82
Epoxy resin

• Chemical reactions

83
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

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Epoxy Resins

• Reaction of homopolymerization

85
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

86
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)

87
Polyimides

• Types
• bis-imides (derived from monomers with 2
  preformed imide groups).
• Typical BMI (bismaleimides)
• Used for lower temperature range 200ºC

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Polyimides

• Properties (show tables)

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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

90
Phenolic resins

• Prepared through condensation polymerization
  between phenol and formaldehyde.
• Large quantity of Water generated (up to 25)
  leading to high void content

91
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

92
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

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Time-temperature-transformation diagrams for
thermosets resins
94
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 gt Tg, rubbery material
• Tcure lt Tg, glassy material
• After vitrification, conversion of monomer almost
  ceases.

95
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

96
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

97
Time-temperature-transformation diagrams for
thermosets resins

• Discussion
• Ungelled glassy state is good for commercial
  molding compounds
• Tgo gt Tprocessing, processed as solid
• Tgo lt Tprocessing, processed as liquid
• Store temperature lt gelTg to avoid gelation
• Resin fully cured when Tg Tg?
• Tg gt Tcure about 40ºC
• Full cure is achieved most readily by cure at T gt
  Tg? and slowly at T lt Tg?.

98
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

99
Unsaturated polyester
100
Unsaturated polyester
101
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.

102
Unsaturated polyester
103
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

104
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

105
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

106
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

107
Vinyl ester

• Resin
• Products of addition polymerization of epoxy
  resin and an unsaturated carboxylic acid (vinyl)
• unsaturated CC 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

108
Vinyl ester
109
Vinyl ester
110
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 )

111
Vinyl ester
112
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

113
Disadvantages of thermosetting resins

• Limited storage life
• Long time to cure
• Low strain to failure
• Low impact resistance
• Large shrinkage on curing

114
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

115
Thermoplastic matrices

• examples
• Conventional
• Nylon
• Polyethylene
• Polypropylene
• Polycarbonate
• Polyester
• PMMA

116
Thermoplastic matrices

• examples
• Advanced (e.g.)

117
Thermoplastic matrices

• examples
• Advanced (e.g.)
• Polyimide

118
Thermoplastic matrices
119
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)

120
Thermoplastic matrices
121
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

122
Metal Matrices

• Examples
• Al, Ti, Mg, Cu and Super alloys
• Reinforcements
• Fibers boron, carbon, metal wires
• Whiskers
• Particulate

123
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

124
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

125
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

126
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

127
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

128
Ceramic Matrices

• Increased toughness through deflected crack
  propagation on fiber/matrix interface.
• Example Carbon/carbon composites