An Analysis of the Two-Bar Ratcheting Behavior Using the Viscoplasticity Theory Based on Overstress (VBO)

Abstract

The ratcheting behavior of the “unsymmetric two-bar system” was investigated by numerical experiments. The two bars are restrained to the same length and are subjected to a constant load. One bar sees cyclic temperature variations, while the other bar is kept at constant temperature. The material models employed are rate independent plasticity (kinematic hardening) and the viscoplasticity theory based on overstress (VBO) matched to represent the cyclic neutral 6061 T6 aluminum alloy elastic and inelastic deformation behavior. For simplicity, temperature-independent material properties were assumed. Numerical analyses were performed to investigate the effects of rate of thermal loading and temperature range. Elastic-inelastic shake down is ultimately achieved due to work hardening. There is a strain range increase until it reaches a steady value. Kinematic hardening and VBO predict almost the same strain range, which, for the case of VBO, is nearly rate-independent. The behavior for both material models is very different for the mean strain. For VBO, the number of cycles to shakedown is rate-dependent and is considerably larger than for kinematic hardening. Finally, the steady-state mean strain and strain range are computed directly for VBO.