Plastic Deformation

· Slip in a single crystal is illustrated opposite. The slip plane (green) has a normal at an angle Φ to the tensile axis, and the slip direction in the slip plane makes an angle λ with the tensile axis.
· The resolved shear stress in the slip direction is given by: τ_res = σ cos λ cos Φ.
· When τ_res becomes larger than the critical shear stress, the slip system becomes active, i.e. Frank Reed sources cause dislocation multiplication on that slip system and plastic deformation occurs.

From: Hull, "Introduction to Dislocations," Pergamon (1965)