Size effects in the torsion of microscale copper wires: Experiment and analysis

The size dependence in the torsional response of microsized polycrystalline copper wires is investigated experimentally using a novel automated torsion balance. Comparing to the corresponding tensile data, we find significant size effects in both the plastic flow stress and initial yielding in torsion, while only slight size effects present in tension. Our micro-torsion tests have high resolution in the low strain region. The experimental observations are explained in terms of a strain gradient plasticity theory with one material length variable.