This paper highlights the observation that the Wilshire equations for failure times and times to various strains, as reported in the original literature, may not be the most appropriate ones for all materials—including the one selected in this study. Further, such appropriateness can be determined by looking at the consistencies between the parameter estimates obtained using minimum creep rates in comparison to using failure times. It is shown, using 1Cr-Mo-V steel as an illustration, that the parameter consistency can be achieved by generalising the Monkman–Grant relation so that it contains a temperature correction. Indeed, the ability of the Wilshire equations to produce meaningful physical parameters, such as the activation energy, is shown to be highly dependent upon a valid specification for the Monkman–Grant relation. It is shown that variations in the measured values for some of the Wilshire parameters (w and k 3) with strain indicate that the causes of deformation are different at different strains and different stresses. Finally, the measured variations in the parameters of the Monkman–Grant relation with strain enable accurate interpolated and extrapolated creep curves to be calculated for any test condition.
Journal of Materials Science, 2014, Vol. 49(1), Pages 329-339, doi: 10.1007/s10853-013-7709-7