Assessment of the Wilshire-Cano-Stewart Model Using Strain Energy Density Dissipation

In this study, strain energy density (SED) is employed as a creep damage parameter to calibrate the Wilshire-Cano-Stewart (WCS) model. The WCS model is an adaptation of the Wilshire equations combined with continuum damage mechanics to enable predictions of creep deformation and damage. In WCS, the analytical calibration methods for the Wilshire equations remain unchanged and the additional damage parameters are found using numerical optimization. Though the WCS model can accurately predict progressive creep deformation, the damage remains phenomenological. Herein, damage is represented as SED. In SED, it is assumed that a material system has a finite amount of energy per unit volume that can be dissipated before failure. Assuming that SED is caused by the accumulation of microstructural defects, the damage process is represented as a scalar value from zero (undamaged) to unity (rupture). By combining the WCS model with SED, damage evolution is pinned physically and can be measured experimentally. Stress rupture, minimum-creep-strain-rate, and creep deformation data are gathered for alloy P91 at 600 °C and stresses from 100 to 200 MPa. The Wilshire constants are analytically determined and compared with the literature. The damage-trajectory constant is calibrated using SED measurements. The new calibration accurately predicts the material response across the range of stresses and temperatures. A comparison between numerical optimization and measured damage-trajectory constants is performed. Parametric simulations verify the interpolation and extrapolation capabilities of this new approach.