CYCLIC HARDENING IN COPPER DESCRIBED IN TERMS OF COMBINED MONOTONIC AND CYCLIC STRESS-STRAIN CURVES

Hardening of polycrystalline copper subjected to tension-compression l oading cycles in the plastic region is discussed with reference to cha nges in flow stress determined from equations describing dislocation g lide. It is suggested that hardening is as a result of the accumulatio n of strain on a monotonic stress-strain curve. On initial loading, th e behaviour is monotonic. On stress reversal, a characteristic cyclic stress-strain curve is followed until the stress reaches a value in re verse loading corresponding to the maximum attained during the precedi ng half cycle. Thereafter, the monotonic path is followed until strain reversal occurs at completion of the half cycle. Repetition of the pr ocess results in cyclic hardening. Steady state cyclic behaviour is re ached when a stress associated with the monotonic stress-strain curve is reached which is equal to the stress associated with the cyclic str ess-strain curve corresponding to the imposed strain amplitude.