Consideration of elastic follow-up in the treatment of combined primary and secondary stresses in fracture assessments

This paper reviews estimates of the factor V used in fitness-for-service codes and in the literature to account for interactions between primary and secondary stress due to crack tip plasticity. A new approach based on a relaxation equation is presented, relevant to both secondary stresses with and without significant elastic follow-up. When elastic follow-up is high this leads to secondary loads acting as primary. In the absence of elastic follow-up, a simplified bound to the interaction is derived which is independent of the magnitude of the secondary stresses. The results are used to develop new proposals for treating combined stresses.

► The paper quantifies primary and secondary stress interactions on fracture. ► A relaxation equation treats secondary stress with and without elastic follow-up. ► For high elastic follow-up this corresponds to secondary loads acting as primary. ► For no follow-up interaction is bounded, independent of secondary stress magnitude. ► New proposals are developed for treating combined stresses in fracture assessments.