The bigger picture:ceramic (CMC)metal (MMC)

naturalpolymer (PMC)

John Summerscales

Upper continuousoperation temperature

from Hancox & Phillips, ICME-2, 1985

Composite matrix Upper continuous operation

temperaturepolymer 400°C

metal (Al) 580°C

ceramic 1000°C

Residual stresses

• CMC and MMC are often manufactured at high-temperatures

• BEWARE: residual stresses resulting from differences in the coefficient of thermal expansion

Ceramic matrix composites (CMC)

• subscripts: f, p, wo eg SiCf, SiCp, SiCw

o fibre, particle, whisker

• reinforcement toughens matrixo minimal or negative effect on modulus

• applications ino radomeso armouro cutting tools o biomedical

Ceramic matrix composites (CMC)• four principal groups

o 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

Ceramic matrix composites (CMC)

• Carbon-carbon compositeso applications in

aircraft and F1 braking rocket motor nozzle throats and exit cones nosetips/leading edges thermal protection systems

Carbon-carbon composites

• carbon fibre preform • impregnate with organic liquid then

pyrolysiso phenolic or furfuryl resins

yield ~55% carbon at 1000°C

o liquid pitch and high isostatic pressure (70 MPa) yield ~85% carbon

• chemical vapour deposition (CVD)o hydrocarbon precursor gaso isothermal, thermal gradient or

differential pressure conditions

Metal matrix composites (MMC)

• three principal (alloy) matrix systemso aluminiumo magnesiumo titanium

• mostly particulate reinforcemento boron-fibre/aluminium used in aerospace

• little advantage to stiffness and strength• gains in creep performance, toughness,

wear resistance, reduced thermal distortion

Metal matrix composites (MMC)• generally high-temperature processes• interdiffusion of matrix/reinforcement

produces a (gradient) interphase• beware galvanic corrosion

o C fibres in Al/Mg matrix opposite ends of electrochemical series

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 mouldfrom 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 retentiono long solidification times.

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

including PCAST processo as LPF, but mould is a cold thin walled vessel

located inside and clamped by pressure vesselo low cost tooling.

• Squeeze casting: high-quality castingo pressurise to 1000-2000 atm during

solidificationo collapses porosity and o increases thermal contact with unheated die

wall resulting in rapid solidification rate.o high capital facility and tooling costs.

MMC Liquid State processes III

• Casting/semi-slurry techniqueo two phase process for (continuous) castingo limited to short-fibre/particulate

reinforcemento Phase 1: dispersal of reinforcement in melto Phase 2: shear dilutiono produces ingots for subsequent reprocessing

• Osprey techniqueo liquid Al alloy atomised in N2 atmosphere

o fed with 5μm (silicon carbide) particleso sprayed onto collector surface.

MMC Liquid State processes IV

MMC Solid State processes I• Low temperature processes with

diffusion bonding.• Foil techniques

Compaction of fibre with foil matrixbelow the solidus temperature:o foil plating by cold rolling o explosion welding o hot pressing (HP) o hot isostatic pressing (HIP)

• Powder techniquesAluminium alloy matrix materialscanned and vacuum-degassedprior to consolidation to minimise surface oxidation and contamination

MMC Solid State processes II

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

Natural composites• Cellulose

o most abundant polysaccharide o notably plant materials

• Chitin/chitosano second most abundant polysaccharide o found in:

crab and shrimp shells (the main commercial source)

various marine organisms, insect cuticle fungi and yeast cells

• Proteinso silk fibres

Natural composites• wood

o timber .. plywood .. MDF .. chipboard

• reinforcementso bast (plant stem) fibres: flax, hemp, juteo leaf fibres: pineapple or sisalo seed fibres: coir or cotton

• bio-based resin systems

• biomimetics

Nacre (abalone/mother-of-pearl)• CaCO3 aragonite crystals

hexagonal platelets: 10-20 µm x 0.5 µm thick

arranged 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 resilient due to adhesion by the "brickwork“ arrangement of the platelets which inhibits transverse crack propagation.

Nacre

• Micrograph from Tomsia et al http://www.physorg.com/news10408.html• Schematic from http://en.wikipedia.org/wiki/Mother_of_pearl

Natural composites

• Arthur MacGregor book:“Bone, antler, ivory, horn: the technology of skeletal materials since the Roman Period” Barnes and Noble, London, 1985.o the definitive work on bonework

from Roman to medieval times.

Polymer matrix composites (PMC)

• Thermosetso AFRP, CFRP, GFRP

• Thermoplasticso AFRTP, CFRTP, GFRTP

sailcloths, tarpaulins, tensile structures (eg Frei Otto)

• Elastomerso cord-reinforced rubber

cotton, rayon, nylon, steel, aramid fibres tyres, hoses, conveyor belts