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The bigger picture: ceramic (CMC) metal (MMC) natural polymer (PMC) John Summerscales Upper continuous operation temperature Composite matrix polymer Upper continuous operation temperature 400°C metal (Al) 580°C ceramic 1000°C from Hancox & Phillips, ICME-2, 1985 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, w eg SiCf, SiCp, SiCw o fibre, particle, whisker o • reinforcement toughens matrix o minimal or negative effect on modulus • applications in radomes o armour o cutting tools o biomedical o Ceramic matrix composites (CMC) • four principal groups o complex glass forming oxides o engineering ceramics o reinforcement by micro-crystalline phases, e.g. Pyrex SiC, Si3N4, SiMON (esp. SiAlON), Al2O3, ZrO2 cement and concrete (prestressed) reinforced concrete pultrusions instead of rebars fibre-reinforced cements o carbon/carbon composites Ceramic matrix composites (CMC) • Carbon-carbon composites o 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 pyrolysis o phenolic or furfuryl resins o yield ~55% carbon at 1000°C liquid pitch and high isostatic pressure (70 MPa) yield ~85% carbon • chemical vapour deposition (CVD) hydrocarbon precursor gas o isothermal, thermal gradient or differential pressure conditions o Metal matrix composites (MMC) • three principal (alloy) matrix systems aluminium o magnesium o titanium o • 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 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 process 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 o 10-15 atm for Saffil preforms 70 atm for 50 v/o carbon fibre high clamping loads, o massive dies for heat retention o long solidification times. o MMC Liquid State processes II • Pressure infiltration casting (PIC), including PCAST process as LPF, but mould is a cold thin walled vessel located inside and clamped by pressure vessel o low cost tooling. o • Squeeze casting: high-quality casting pressurise to 1000-2000 atm during solidification o collapses porosity and o increases thermal contact with unheated die wall resulting in rapid solidification rate. o high capital facility and tooling costs. o MMC Liquid State processes III • Casting/semi-slurry technique o o o o o two phase process for (continuous) casting limited to short-fibre/particulate reinforcement Phase 1: dispersal of reinforcement in melt Phase 2: shear dilution produces ingots for subsequent reprocessing MMC Liquid State processes IV • Osprey technique liquid Al alloy atomised in N2 atmosphere o fed with 5μm (silicon carbide) particles o sprayed onto collector surface. o MMC Solid State processes I • Low temperature processes with diffusion bonding. • Foil techniques Compaction of fibre with foil matrix below the solidus temperature: foil plating by cold rolling o explosion welding o hot pressing (HP) o hot isostatic pressing (HIP) o MMC Solid State processes II • Powder techniques Aluminium alloy matrix materials canned and vacuum-degassed prior to consolidation to minimise surface oxidation and contamination MMC secondary processing • extrusion, forging, rolling, stamping • superplastic forming • machining o superhard cutting and grinding tools AJM: CHM: EBM: EDM: LBM: PAM: USM: abrasive waterjet cutting chemical milling electron beam machining electro-discharge machining laser beam machining plasma arc machining ultrasonic machining Natural composites • Cellulose most abundant polysaccharide o notably plant materials o • Chitin/chitosan second most abundant polysaccharide o found in: o crab and shrimp shells (the main commercial source) various marine organisms, insect cuticle fungi and yeast cells • Proteins o silk fibres Natural composites • wood o timber .. plywood .. MDF .. chipboard • reinforcements bast (plant stem) fibres: flax, hemp, jute o leaf fibres: pineapple or sisal o seed fibres: coir or cotton o • 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) • Thermosets o AFRP, CFRP, GFRP • Thermoplastics o AFRTP, CFRTP, GFRTP sailcloths, tarpaulins, tensile structures (eg Frei Otto) • Elastomers o cord-reinforced rubber cotton, rayon, nylon, steel, aramid fibres tyres, hoses, conveyor belts