Analysis of elastic-plastic torsion of circular bars at large strains

Large elastic-plastic torsion of uniform circular bars is investigated numerically, using special finite elements. Two end conditions corresponding to fixed-end torsion and free-end torsion, resp., are considered, taking full account of the axial effects. The analysis is carried out using an isotropic hardening as well as a recently proposed large deformation kinematic hardening model. Either linear hardening or power law hardening uniaxial stress-strain curves are assumed in the analysis. Results are presented in terms of predicted torque vs. twist curves for all cases. Furthermore, we present axial force vs. twist curves for fixed-end torsion or elongation vs. twist curves for free-end torsion. Special attention is paid to the so-called plastic spin, a concept which has recently been identified to play a key role in the description of induced anisotropy. The differences between free-end and fixed-end torsion are emphasized.