Cyclic Viscoplasticity Testing and Modeling of a Service Aged P91 Steel

Abstract

A serviceaged P91 steel was used to perform an experimental program of cyclic mechanical testing in the temperature range of 400 آ°C–600 آ°C, under isothermal conditions, using both sawtooth and dwell (inclusion of a constant strain dwell period at the maximum (tensile) strain within the cycle) waveforms. The results of this testing were used to identify the material constants for a modified Chaboche, unified viscoplasticity model, which can deal with ratedependant cyclic effects, such as combined isotropic and kinematic hardening, and timedependent effects, such as creep, associated with viscoplasticity. The model has been modified in order that the twostage (nonlinear primary and linear secondary) softening which occurs within the cyclic response of the serviceaged P91 material is accounted for and accurately predicted. The characterization of the cyclic viscoplasticity behavior of the serviceaged P91 material at 500 آ°C is presented and compared to experimental stress–strain loops, cyclic softening and creep relaxation, obtained from the cyclic isothermal tests.