DEVELOPMENT OF A PROGRAM BASED ON RE-MESHING FOR NATURAL CRACK GROWTH OF MULTIPLE CRACKS

Nuclear power plant facilities undergo periodic in-service inspections for structural integrity assessment. During these inspections, when multiple cracks are detected, the stress distribution and fracture mechanics parameters at the crack tips can be significantly influenced by the adjacent cracks. Therefore, to accurately conduct multiple crack evaluation and crack growth, it is essential to consider such crack interactions. Existing code and standards (ASME Section XI, API 579, and BS7910) provide guidelines for the evaluation and coalescence produce for multiple cracks. However, these conventional procedures may assume conservative evaluations, such as merging two close elliptical cracks into a single larger ellipse. In this study, a program based on adaptive meshing through finite element analysis was developed which includes generating crack tip meshes suitable for coalescing multiple cracks. After crack coalescence, criteria for crack tip relaxation considering the spider-web mesh were applied, and the coalescence distance criterion from ASME Section XI was employed. Fatigue crack growth was performed using both the coalescence criteria applied in the program and those from ASME Section XI, and the crack growth results were compared. This analysis aimed to evaluate the impact of the coalescence assumptions from ASME Section XI on crack assessment.