Strain Hardening at Large Strains

The strain hardening properties of various f.c.c. metals have been investigated at large strains by means of torsion tests of short thin-walled cylinders. The results show that Stage IV occurs in all cases provided that a low enough test temperature is used; it and is a nearly constant hardening rate of 2.10-4 G in terms of resolved flow stress. Stage IV strain hardening has been modeled by considering the effects of accumulation of dislocation debris, such as dipoles and loops, on the “saturation” stress. The “saturation” stress that can be obtained by extrapolation of Stage III is now a limiting flow stress that slowly increases with the accumulation of debris. The model reproduces the sharp transition from Stage III to Stage IV that occurs experimentally at low temperatures and, for a reasonable choice of parameters, the rate of hardening in Stage IV.