Composites Fiberglass increasing the modulus of epoxies Nacre brick ceramic and mortar biopolymer structure effective at deflecting cracks Tungsten carbide cobalt hard particles in a ductile matrix 1 Carbon fiber reinforced polymer CFRP composites drive weight savings in aerospace applications Boeing 777 1995 Boeing 787 2011 15 wt CFRP 55 wt Al alloys 10 wt Ti alloys 15 wt Steels 50 wt CFRP 80 vol 20 wt Al alloys 15 wt Ti alloys 10 wt Steels Particulate and short fiber composites are not as effective at strengthening and stiffening compared to continuous fiber composites Why is this and at what length can we assume that our fibers are long enough to act like continuous fiber composites 3 Fiber Reinforced Composites Key Concept No load is transferred at the extremities of the fiber Therefore one needs a fiber of critical length lc to transfer load from the matrix to the fiber lc minimum length such that the full benefit of fibers is obtained i e the matrix is able to transfer the load to the fibers 4 Fiber Reinforced Composites are inherently anisotropic properties are direction dependent The value of Young s modulus depends on the direction of applied loading 5 Rather than a fiber reinforced material we will consider a layered ceramic metal composite Transverse Loading With transverse loading we have an isostress condition the stress on each layer is the same but the amount of strain will be different for the metal and the ceramic unless they have the same Young s modulus Assumption The composite obeys Hooke s law e g we are considering small strains 6 Longitudinal Loading With longitudinal loading we have an isostrain condition the strain on each layer is the same but the amount of stress will be different for the metal and the ceramic unless they have the same Young s modulus Again we are assuming that the composite obeys Hooke s law 7 Estimating Calculating Composite Properties Consider a composite of 50 vol each of copper E 125 GPa and alumina Al2O3 E 390 GPa The highest possible upper bound Young s modulus is in longitudinal loading E comp E c X c E m 1 X c 390 0 50 125 0 50 257 5 GPa The lowest possible lower bound Young s modulus is in transverse loading E comp EcEm 390 125 189 3 GPa X c E m 1 X c E c 0 50 125 0 50 390 8 Modulus varying with different proportions of the two materials 9 Matrix and Fiber Properties of Fiber Reinforced Composites Fibers main strengthening and stiffening phase Common Fibers Specific Gravity Strength GPa Modulus GPa Specific Strength Kevlar Polymer Aramids Glass Carbon High Carbon Steel Wire Matrix transfer the load to the fibers Common Matrix Specific Gravity Strength MPa Modulus GPa Polyester Epoxy 10
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