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.