Tensile instability in face-centred cubic materials

A study of plastic instability in tension, which occurs well before the Considère criterion is met, is reported for face-centred cubic single crystals. The observations show that the instability is caused by a sudden effective decrease in work hardening resulting from the operation of a new dominant shear system. The change of dominant shear system is always accompanied by strain localization phenomena. In general, the rate of work hardening at the point of strain localization is appreciably higher than the flow stress. It is concluded that strain localization is a consequence of change of the deformation mechanism rather than a gradual decrease in the rate of work hardening. The dependence of this type of instability on crystal orientation, chemical composition and deformation temperature is discussed Premature strain localization was also observed in polycrystalline specimens at high stresses; this phenomenon is also discussed.