Evaluation of Coalescence Criteria for Parallel Cracks

Abstract

When multiple cracks approach one another, the stress intensity factor (SIF) is likely to change due to the interaction of the stress field. Since the change in the SIF is not always conservative in structural reliability evaluations, this interaction between multiple cracks must be taken into account. Section XI of the ASME Boiler and Pressure Vessel Code (Sec. XI) provides a flaw characterization method for considering multiple crack interactions. In Sec. XI, adjacent cracks are replaced by a coalesced single combined crack if they are located within a certain distance. However, no systematic analysis of the SIF for interacting parallel surface cracks is provided. Furthermore, the background of the coalescence criterion prescribed in Sec. XI is not clear. In this study, the SIF of interacting parallel cracks was calculated using the finite element method. A coalescence criterion for parallel cracks was then proposed based on the calculation results. A simplified mesh generation method was adopted in order to improve the complexity of the mesh generating procedure, which uses a transitional mesh, referred to as a “Tie Block.”