Incorporating the Wilshire equations for time to failure and the minimum creep rate into a continuum damage mechanics for the creep strain of Waspaloy

In this paper, a new constitutive model is presented that combines the Wilshire equations with a modified Kachanov-Rabotnov continuum damage mechanics (CDM) to enable the prediction of uniaxial creep curves that contain both a primary and tertiary stage. Another advantage of this approach is that the Wilshire equations have been shown to accurately extrapolate the operational failure times and minimum creep rates from very short-term tests. This approach also removes the need to estimate the Wilshire time to strain equation at numerous different strains. A simple but multi-step procedure is also introduced for estimating the unknown parameters of this model. When applied to Waspaloy data, the model was shown to represent the shape of the experimental creep curves reasonably well especially at low and high strains and provides reasonable creep curve predictions - with percentages errors averaging around 4-5%.