Cyclic torsion of micron-scale polycrystalline copper wires was experimentally studied. It was found that cyclic hardening is more pronounced with larger strain amplitude under symmetric cyclic straining. The mean stress relaxation is accelerated with larger initial strain and smaller strain amplitude under asymmetric cyclic straining. Meanwhile, both sample size and grain size effects were observed. That is the mean stress relaxation increases with decreasing sample size and grain size. The grain size effect is caused by an elevated internal stress in wire with smaller grain size. The observed sample size effect is attributed to the internal stress induced by geometrically necessary dislocations.

实验研究了微米级多晶铜线的循环扭转。发现在对称循环应变下，随着应变幅度的增大，循环硬化更加明显。在不对称循环应变下，平均应力松弛以较大的初始应变和较小的应变幅度加速。同时，观察到样品尺寸和晶粒尺寸的影响。也就是说，平均应力松弛随着样品尺寸和晶粒尺寸的减小而增加。晶粒尺寸效应是由晶粒尺寸较小的钢丝内应力升高引起的。观察到的样本大小效应归因于几何上必要的位错引起的内部应力。