I will refer the user to a MS Thesis entitled: "INCORPORATION OF A GENERAL STRAIN-TO-FAILURE FRACTURE CRITERION INTO A STRESS-BASED PLASTICITY MODEL THROUGH A TIME-TO-FAILURE SOFTENING MECHANISM", by Matthew Scot Swan
Also: http://www.springer.com/cda/content/document/cda_downloaddocument/9781848001886-c1.pdf
