Last class -

Creep, relaxation, recovery

silicones polycarbonate aramidPVC

epoxyToday –

H2C-C-C{-O- -C- -O-}nC-C-CH2

H-C-HH

H-C-HH

epoxy

H

H OO

H

H

hardenerH2N-R-NH2

Prepregs

Some specific polymers

Composites - overview

Example - carbide tools (previously discussed)

Co matrix phase

angular WC fragments

Composites - overview

Artificial combination of matrix phase & dispersed phase

Matrix:metal, alloyceramic mat'lpolymer

Dispersed phase:particulatefiber

Composites - metal matrix composites (MMCs) Particulates:

ThO2-dispersed Ni (TD Ni)sintered Al powder (SAP)

- except strengthening maintained at hi T

Improves:strengthcreep resistancehi T corrosion resistance

Works like precipitation hardening

Composites - metal matrix composites (MMCs) Fibers:

Conts - C, SiC, B, Al2O3

Disconts - C, Al2O3 , SiC whiskers

May get rxn betwn phases at hi T

Matrix mat'ls

Composites - ceramic matrix composites (CMCs)

Particulates, fibers:SiC, B, Al2O3 , C, SiC & Si3N4

whiskers

Improve fracture toughness:slow crack growth

deflect crack tipsredistribute stresses around crack

tipsbridge crack tips

Matrix

Composites - polymer matrix composites (PMCs)

Fibers:mainly - glass (GFRPs), carbon (CFRPs),

aramid,others - B, SiC, Al2O3

Composites - polymer matrix composites (PMCs) Matrix

Composites - polymer matrix composites (PMCs)

Very common - polyesters, vinyl esters

Composites

Role of matrix in FR composites:a. transfer stresses betwn fibersb. provide barrier to environmentc. protect fibers

Matrix/fiber bond:matrix must wet fiber physical & chemical bond desirablemechanical interlocking

Fibers frequently coated w/ coupling agent

non-coupled

Composites

coupled

Composites

Fibers - variablesamountfiber lengthdistributionorientation

Fiber orientation can berandom aligned intermediate