Determination of the Interaction Between Primary and Secondary Stresses Using an Idealised Model

When conducting an assessment of the integrity of a structure the user is directed to classify the stresses as either primary stress or secondary stress. Residual stresses are usually classified as secondary stresses unless they exhibit significant elastic follow-up. In this paper the authors have first summarised current methods and origins of the UK R6 structural integrity assessment methodology for combining primary and secondary stresses. Then, using an idealised model, a new approach has been developed to examine how fixed-displacement secondary stresses interact and redistribute; this model permits a combined reference stress to be determined directly. This combined reference stress is intrinsically linked to the effect of elastic follow-up within the structure and provides a direct measure of how the residual stress relaxes between the extremes of fixed-load and fixed-displacement conditions. The results have been compared with the existing approaches in R6 and it has been demonstrated that the R6 method can be either conservative or non-conservative, depending on the degree of elastic follow-up and residual stress redistribution.Copyright © 2012 by ASME