MEEN 431 Composite Materials HW: 1 (Due Date: 01/29/2018, Monday) 1. The modulus

Question

MEEN 431 Composite Materials HW: 1 (Due Date: 01/29/2018, Monday) 1. The modulus and tensile strength of a composite are reported as 15 GPa and 230 MPa, respectively. Assuming the density of the composite is 1.85 g/em2, calculate the strength- weight ratio and modulus to weight ratio for the composite 2. To reduce the material cost, an engineer decides to use a hybrid beam instead of an all- carbon fiber beam. Both beams have the same overall dimensions. The hybrid beam contain carbon fibers in the outer layers and either E-glass or Kevlar 49 fiber in the core. The matrix used is an epoxy. Costs of these materials are as follows: Carbon fiber - epoxy matrix $25.00/lb, density 1.55 g/cm E-glass fiber - epoxy matrix Kevlar 49 fiber - epoxy matrix:$8.00/lb, density 1.38 g/em :$1.20/1b, density 1.85 g/em3 The total carbon fiber - epoxy thickness in the hybrid beam is equal to the core thickness. Compare the percentage of weight penalty and cost savings for each hybrid beam over an all- carbon fiber beam.

Explanation / Answer

(1) solution ;-

Given data, ;- modules of elasticity (E) = 10 GPA = 15 ×10^9 pa

tensile strength = 230 MPa = 230 x 106 Pa

density = 1.85 g/cm3 = 1.85 x 10-3 kg / (10-6 ) m3 = 1850 kg/m3

strength weight ratio = strength / density = 230 x 106 Pa / ( 1850 kg/m3 ) = 124324.3243 Pa-m3 /kg

modulus weight ratio = 15 x 109 Pa / ( 1850 kg/m3 ) = 8108108.108 Pa-m3 /kg

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