Predictions of elastic-plastic crack driving force and redistribution under combined primary and secondary stresses - Part 1: Analytical investigation

Many engineering components, particularly those containing weldments, may enter service with or develop small crack-like defects. In non-stress-relieved welds, or under thermal stresses, such defects will experience both primary and secondary stresses combined. This paper describes a new function, g, that has been introduced to detail the plasticity interaction under combined loading within structural integrity assessment methods. This function has been based on the Option 2 failure assessment curve in the R6 approach to structural integrity assessment and has been determined from finite element analyses of an externally cracked cylinder under combined primary and secondary loadings. The g function method has been used in the assessment of a series of other cracked geometries subject to loadings which include secondary stresses arising from both thermal gradients and weld residual stresses. The results presented show that the g approach can successfully be extended to the assessment of these other geometries and loading combinations and provides reasonably accurate and less conservative assessments than existing methods presented in R6. A second paper, " Part 2: Experimental Application" , compares the application of the g approach with data from experiments performed over a range of plasticity development.