the bigger picture: ceramic (cmc) metal (mmc) natural polymer (pmc) john summerscales
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The bigger picture:ceramic (CMC)metal (MMC)
naturalpolymer (PMC)
John Summerscales
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Upper continuousoperation temperature
from Hancox & Phillips, ICME-2, 1985
Composite matrix Upper continuous operation
temperaturepolymer 400°C
metal (Al) 580°C
ceramic 1000°C
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Residual stresses
• CMC and MMC are often manufactured at high-temperatures
• BEWARE: residual stresses resulting from differences in the coefficient of thermal expansion
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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
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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
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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
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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
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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
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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
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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 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.
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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.
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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
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• 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
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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)
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• Powder techniquesAluminium alloy matrix materialscanned and vacuum-degassedprior to consolidation to minimise surface oxidation 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/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
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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
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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.
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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 Period” Barnes and Noble, London, 1985.o the definitive work on bonework
from Roman to medieval times.
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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