Size effect in cyclic torsion of micron-scale polycrystalline copper wires

Abstract

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.