6.27 The surface of a steel machine member is subjected to principal stresses of 200 MPa and 100 MPa. What tensile yield strength is required to provide a safety factor of 2 with respect to initial yielding: According to the maximum‐shear‐stress theory? According to the maximum‐distortion‐energy theory? [Ans.: (a) 400 MPa, (b) 346 MPa]