A single crystal of a metal is oriented for a tensile test such that its slip plane normal makes an angle of 64.2° with the tensile axis. Three possible slip directions make angles of 30°, 48°, and 78° with the same tensile axis.

(a) Which of these three slip directions is most favored?

(b) If plastic deformation begins at a tensile stress of 1.6 MPa (232.1 psi), determine the critical resolved shear stress for this metal