Constraints Imposed by the Wilshire Methodology on Creep Rupture Data and Procedures for Testing the Validity of Such Constraints: Illustration Using 1Cr-1Mo-0.25V Steel

A new parametric approach, termed the Wilshire equations, offers the realistic potential of being able to accurately life materials operating at in service conditions from accelerated test results lasting no more than 5000 hours. These Wilshire equations contain discontinuities that have in the literature been interpreted either in terms of changing deformation mechanisms or changes in where deformation occurs within a material (i.e., within boundaries or crystals). This paper demonstrates that the rather restrictive nature of these discontinuities within the Wilshire equations can lead to problems in identifying an appropriate model for long-term life prediction. An alternative framework is developed that removes these restrictions but still maintains the fundamental nature and characteristics of the Wilshire methodology. Further, when this alternative structure is applied to 1Cr-1Mo-0.25V steel, it produces more accurate and realistic looking long-term predictions of the time to failure.