Critical Fracture Stress of a Plate with an Inclined Crack

A large thick plate of steel contains a crack of length 5 mm oriented at an angle s = 30° with respect to the direction of applied uniaxial stress σ. Calculate the angle of initial crack extension and the value of the critical stress σc for crack growth according to the strain energy density criterion when the stress σ is (a) tensile and (b) compressive. KIc= 60 MPa√m, E = 210 GPa, v = 0.3.