15-1: A uniaxial tensile stress of 100ksi is being measured in iron by 211 diffraction of x-rays at =0 and 45. Take the lattice parameter a of the stress-free iron to be 2.8665A,E=30106 psi, and u=0.29. (a) Calculate d and d0 to five significant figures. (b) What percent error is made in replacing (dd0)/d0 by [dd(=0)/d(=0)] in Equation 15.18 ? d0dd0=E1+sin2E(11+22)