cmcmmcpmc

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The bigger picture:ceramic (CMC)

metal (MMC)naturalpolymer (PMC)

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Upper continuousoperation temperature

from Hancox & Phillips, ICME-2, 1985

Composite matrix Upper continuousoperation

temperature

polymer 400C

metal (Al) 580C

ceramic 1000C

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Residual stresses

CMC and MMC are often manufactured athigh-temperatures

BEWARE: residual stresses

resulting from differences inthe coefficient of thermal expansion

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Ceramic matrix composites (CMC)

subscripts: f, p, wo eg SiCf, SiCp, SiCwo fibre, particle, whisker

reinforcement toughens matrixo minimal or negative effect on modulus

applications in

o radomeso armour

o cutting tools

o biomedical

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four principal groupso complex glass forming oxides

reinforcement by micro-crystalline phases, e.g. Pyrex

o engineering ceramics

SiC, Si3N4, SiMON (esp. SiAlON), Al2O3, ZrO2

o cement and concrete

(prestressed) reinforced concrete

pultrusions instead of rebars fibre-reinforced cements

o carbon/carbon composites

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Carbon-carbon compositeso applications in

aircraft and F1 braking

rocket motor nozzle throats and exit cones nosetips/leading edges

thermal protection systems

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Carbon-carbon composites

carbon fibre preform impregnate with organic liquid then pyrolysis

o phenolic or furfuryl resins

yield ~55% carbon at 1000C

o liquid pitch and high isostatic pressure (70 MPa)

yield ~85% carbon

chemical vapour deposition (CVD)o hydrocarbon precursor gas

o isothermal, thermal gradient ordifferential pressure conditions

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Metal matrix composites (MMC)

three principal (alloy) matrix systemso aluminium

o magnesium

o titanium

mostly particulate reinforcement

o boron-fibre/aluminium used in aerospace

little advantage to stiffness and strength

gains in creep performance, toughness,wear resistance, reduced thermal distortion

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Metal matrix composites (MMC)

generally high-temperature processes

interdiffusion of matrix/reinforcementproduces a (gradient) interphase

beware galvanic corrosion

o C fibres in Al/Mg matrix

opposite ends of electrochemical series

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MMC Liquid State processes I Liquid pressure forming (LPF)

including the Cray processo similar to RTM with molten metal

fed into an evacuated fibre-filled mould

from below by pressure.o gases and volatiles vented from mould top.

o high pressures

10-15 atm for Saffil preforms

70 atm for 50 v/o carbon fibre

o high clamping loads,

o massive dies for heat retention

o long solidification times.

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MMC Liquid State processes II Pressure infiltration casting (PIC),

including PCAST process

o as LPF, but mould is a cold thin walled vessellocated inside and clamped by pressure vessel

o low cost tooling.

Squeeze casting: high-quality casting

o pressurise to 1000-2000 atm during solidification

o collapses porosity ando increases thermal contact with unheated die wall

resulting in rapid solidification rate.

o high capital facility and tooling costs.

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MMC Liquid State processes III

Casting/semi-slurry techniqueo two phase process for (continuous) casting

o limited to short-fibre/particulate reinforcement

o Phase 1: dispersal of reinforcement in melto Phase 2: shear dilution

o produces ingots for subsequent reprocessing

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Osprey techniqueo liquid Al alloy atomised in N2 atmosphere

o fed with 5m (silicon carbide) particles

o sprayed onto collector surface.

MMC Liquid State processes IV

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MMC Solid State processes I Low temperature processes with diffusion

bonding.

Foil techniquesCompaction of fibre with foil matrix

below the solidus temperature:o foil plating by cold rolling

o explosion welding

o hot pressing (HP)

o hot isostatic pressing (HIP)

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Powder techniquesAluminium alloy matrix materialscanned and vacuum-degassed

prior to consolidation to minimise surfaceoxidation and contamination

MMC Solid State processes II

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MMC secondary processing extrusion, forging, rolling, stamping

superplastic forming

machining

o superhard cutting and grinding tools

AJM: abrasive waterjet cutting

CHM: chemical milling

EBM: electron beam machining

EDM: electro-discharge machining LBM: laser beam machining

PAM: plasma arc machining

USM: ultrasonic machining

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Natural composites Cellulose

o most abundant polysaccharide

o notably plant materials

Chitin/chitosan

o second most abundant polysaccharide

o found in:

crab and shrimp shells (the main commercial source)

various marine organisms, insect cuticle fungi and yeast cells

Proteins

o silk fibres

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Natural composites

wood

o timber .. plywood .. MDF .. chipboard

reinforcementso bast (plant stem) fibres: flax, hemp, jute

o leaf fibres: pineapple or sisal

o seed fibres: coir or cotton

bio-based resin systems

biomimetics

( b l / h f l)

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Nacre (abalone/mother-of-pearl)

CaCO3 aragonite crystals

hexagonal platelets: 10-20 m x 0.5 m thickarranged in a continuous parallel lamina.

layers separated by sheets of organic matrix

composed of elastic biopolymers(such as chitin, lustrin and silk-like proteins).

brittle platelets and thin elastic biopolymers

makes the material strong and resilientdue to adhesion by the "brickwork

arrangement of the plateletswhich inhibits transverse crack propagation.

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Nacre

Micrograph from Tomsia et al http://www.physorg.com/news10408.html

Schematic from http://en.wikipedia.org/wiki/Mother_of_pearl

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Natural composites

Arthur MacGregor book:Bone, antler, ivory, horn:the technology of skeletal materials since

the Roman PeriodBarnes and Noble, London, 1985.

o the definitive work on boneworkfrom Roman to medieval times.

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Polymer matrix composites (PMC)

ThermosetsoAFRP, CFRP, GFRP

Thermoplastics

oAFRTP, CFRTP, GFRTP sailcloths, tarpaulins, tensile structures (eg Frei Otto)

Elastomers

o cord-reinforced rubber cotton, rayon, nylon, steel, aramid fibres

tyres, hoses, conveyor belts

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