For polycrystalline magnesium the coef?cient of thermal expansion is 25.2 × 10-6/?C and Young's modulus is 68.4 GPa. Parallel to the c-axis of a single crystal the coef?cient of thermal expansion is 24.3 × 10-6/? and Young's modulus is 80.9 GPa. Estimate the stress parallel to the c-axes of grains in a randomly oriented polycrystal when the temperature is changed by 100?C. Assume that the dimensional change parallel to the c-axis of the grain is the same as that in the polycrystal. For simplicity, assume also that the stress in the polycrystal is negligible.