By Guiyi Wu
Residual stress is one of the key factors which could contribute to the failure of an engineering structure. Classification of residual stress into primary or secondary stresses or a mixture of the two depends on the level of elastic follow-up, which is a complex phenomenon. Primary stresses are those stresses arising from loads which contribute to plastic collapse while secondary stresses are those stresses arising from loads which do not contribute to plastic collapse. In the absence of a specific definition of elastic follow-up or an acceptable guidance on determining elastic follow-up, engineers are left with the options of either performing expensive and time-consuming nonlinear finite element analysis or justifying secondary stresses to produce no significant elastic follow-up. Guidance on the nature of residual stresses is required in order to perform engineering critical assessment. Hence, a comprehensive understanding of elastic follow-up is needed to assist the classification of residual stresses.