Engineering Board Exam Reviewer · Engineering Materials · medium

A unidirectional composite has 60% by volume carbon fibers (E = 230 GPa) in an epoxy matrix (E = 3.5 GPa). What is its longitudinal modulus (isostrain)?

1. 139.4 GPa
2. 8.55 GPa
3. 116.8 GPa
4. 94.1 GPa

Answer

A. 139.4 GPa

Solution

Rule of mixtures: Ec = VfEf + VmEm = 0.6(230) + 0.4(3.5) = 139.4 GPa.

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