Methods to Determine the Critical Damage Criterion of the Kachanov-Rabotnov Law

Considerable effort has gone towards the implementation of continuum damage mechanics (CDM) laws for the creep damage assessment of high temperature components. Often critical damage is considered to be reached when damage is equal to unity. Analytical methods have demonstrated that for various alloys critical damage is much less than unity and is dependent on stress and temperature. Few studies have been conducted to evaluate and correct this problem. In this paper, an examination of the theory of critical damage is conducted. Based on theory, a new critical damage criterion is introduced. A comparison between Penny and the new critical damage criterion will be conducted to determine the most viable criterion. Damage is introduced into life, strain, and mixed life fraction rules to demonstrate the influence damage has on rupture under thermo-mechanical loading.