Answer
$E = 194.50 GPa$
Work Step by Step
Given:
The modulus of elasticity for spinel $(MgAl_{2}O_{4})$ having 5 vol% porosity is 240 GPa ($35 \times 10 ^{6} psi$).
Required:
Modulus of elasticity for 15 vol% porosity.
Solution:
Using Equation 12.9:
$E =E_{0}(1 -1.9P + 0.9P^{2}) =(264.54 GPa)(1 -1.9(0.15) + 0.9(0.15)^{2}) = 194.50 GPa$