Fracture life for constant load creep tests and relationship with fracture mechanisms

Abstract

The theory of constant load uniaxial tests and constant pressure tube burst tests is compared with observed values of minimum creep rate e _m and time to failure t _f. It is shown that the product e _m t _f can exceed the asymptotic value 1/n (1/2n for tubes) at large failure strains, where n is the stress exponent for creep. A fracture model based on cavity growth mechanisms is developed for 20Cr-25Ni-Nb stainless steel. The predictions are compared with the observed values and related to the Monkman–Grant equation. It is shown that the constants in the latter equation incorporate the creep and failure mechanisms.