Comparison of the cyclic stress-strain behaviour of single-and 〈111〉 multiple-slip-oriented copper single crystals

The stress-strain behaviours of single- and multiple-slip-oriented copper single crystals were compared at a constant plastic strain amplitude in the plateau range of the cyclic stress-strain curve. The single slip orientation was 5° from [011] towards [112], and the multiple slip orientation [111]. The results obtained for single-slip-oriented crystals corresponded closely to those reported in earlier work and only minor differences could be seen. For multiple-slip-oriented crystals a strong initial hardening appeared from the beginning of fatigue cycling with a clear peak appearance subsequently; this was followed by a softening period which did not lead to any saturation value. Two distinct ranges, I and II, were observed as a function of the applied γp1 and these were respectively lower and higher than 0.1% for multiple-slip-oriented crystals. The energy parameter βE gave information about persistent slip band initiation in single-slip-oriented crystals but it seemed to be difficult to apply it to multiple-slip-oriented crystals because of the activity of many different slip systems.