Nonlocal effects in torsional deformation

The stress distribution in torsionally deformed cylindrical polycrystalline copper samples was investigated. The strain in torsional deformation chang es with distance from the torsional axis and thus the local extent of work hardening and consequently the local flow stress changes as well. The varia tion of the flow stress with radial position in the samples was measured by microhardness tests. It was found that except for the near-axis region the local flow stress call be correctly calculated by the Nadai evaluation fro m the experimentally measured torque versus torsional angle function. Harde ning is observed in the axis of the torsionally deformed samples in spite o f the fact that the shear strain is zero here. The hardening obtained in th e axis depends approximately linearly on the torsional angle, and it increa ses with grain size. This effect is interpreted by introducing nonlocal eff ects in the continuum description. (C) 2000 Elsevier Science S.A. All right s reserved.