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530.352 Materials Selection. Lecture #9: Structure and elastic properties of CMC’s Tuesday September 27 th , 2005. Composites. Matrix + Metal (MMC) Al (most widely used) and Ti Ceramic (CMC) Polymeric (PMC) Thermoset
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530.352 Materials Selection Lecture #9: Structure and elastic properties of CMC’sTuesday September 27th, 2005
Matrix + Metal (MMC) Al (most widely used) and Ti Ceramic (CMC) Polymeric (PMC) Thermoset Epoxy (most widely used), polyimides (max T stability), cyanate esters, etc. Thermoplastic Poly Ether Ether Keytone (PEEK) – can be remolded Reinforcement Particulate (in MMC) Whiskers (chopped fibers) Continuous fiber Fiberglass (cheap, most common) Kevlar Graphite Carbon Poly Acrylic Nitrile (PAN) Boron SiC Composites are:
Polymer Resin Comparison From “PrePreg Technology”, Hexcel Composites
Boron b-SiC Reaction Zone Reaction Zone W Filament C Monofilament SiC Non-Stoichiometric SiC Fiber Materials
SiC Fiber Carbon Core Coating SiC
800 700 600 500 400 300 200 100 0 10 20 30 40 50 60 70 80 Fiber Comparison Carbon Boron UHS SiC HS PAN IM HM UHM Tensile Strength (ksi) Aramid Glass Carbon MesoPitch Carbon Pitch Tensile Modulus (Msi) From “Composite Materials: Science and Engineering”, K.K.Chawla
Composite forms: • Prepreg Tape • Fibers are ‘pre-impregnated’ into matrix which is partially cured but tacky • All fibers aligned in single direction • Tape ~ 12” wide and any length • Prepreg Cloth • Fibers woven to provide strength/stiffness in 2 directions • Woven cloth “pre-impregnated” w partially cured resin • Cloth ~ 36” wide • Different weaves give different drape • Preform • Fibers stitched, woven, or braded into complicated 3D shapes
What is a Prepreg? From “PrePreg Technology”, Hexcel Composites
Composite Fabrication: Batch acceptance Lay up Bagging Assembly Inspect Cure
Voight Model Iso-strain A = B = Av. = VA A + VBB Av. E = Av. / = VAA / + VBB / Ecomposite = VA EA + VB EB A B
Reuss Model Iso-stress A = B = Av. = VA A + VBB Av. = VA A + VB B 1 / Ecomposite = VA / EA + VB / EB A B