a uniaxial composite material is made into a circular rod with a 1.27 cm diameter from 70 vol % continuous carbon fibers and 30 vol % epoxy. The rod is subject to an axial force of 100,000 N. The composite material in Example Problem 12.1 is to be replaced with a less expensive composite made of 70 vol % continuous E-glass fibers and 30 vol % epoxy. The elastic moduli are 5 GPa for the epoxy resin and 72.4 GPa for the E-glass.
(a) Compare the elastic modulus, composite strain, fiber and matrix stresses, and density of this composite with the carbon epoxy composite in Example Problem 12.1. Use the density of UHM carbon, and assume the density of the epoxy is 1.2 g/cm3.
(b) Can both the E-glass fiber and matrix withstand the applied force?
(b) This stress is in the midrange of the tensile strength of the epoxy matrix material, thus it is quite possible that the epoxy matrix will fracture in this design. In this composite the fibers only carry 14 times as much stress as the matrix; whereas in the carbon epoxy composite they carried 100 times the stress as the matrix.
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