Latent hardening in cyclic deformation of copper single crystals

In order to explore latent hardening produced by cyclic deformation, single crystals of copper oriented for single slip were first cycled at strain amplitudes corresponding to those of the plateau in the cyclic stress-strain curve, and subsequently sectioned for compression testing. The specimens were cycled enough to form persistent slip bands, and orientations in the secondary test were chosen to excite selectively coplanar or non-coplanar slip systems. Coplanar systems were found to be similar in hardening to the primary system, but non-coplanar systems showed a latent hardening ratio of about 1.25. If the plastic shear strain amplitude of the initial cycling was greater than 2×10⁻³ (the threshold for producing secondary slip), then the hardening rate in the secondary test was high. If the cyclic strain amplitude was less than 2×10⁻³, the latent yield stress was high because of the frictional effect of the loop patches, but the hardening rate was found to be low.