Estimate the strain energy of a straight screw dislocation per b length of dislocation line, assuming R ~ 1 cm, r0 ~ 10-8cm, b ~ inter atomic spacing and shear Modulus =86 Gpa??Compare the result with vacancy formation energy: Wvac~ 0.5 - 1 eV and discuss the significance. (b) For Fe of dislocation density of 108 cm/cm3, estimate the strain energy per unit volume. Assuming the shear modulus of Fe is 86 GPa and the Burgers vector is 0.248 nm.