In nuclear power plant, there is a proximity rule to evaluate multiple inner cracks [1]. Inner cracks are generated inside of the structure in different manners. There are many parameters which affects the growing processes of inner cracks. They are; locations, slant angles, aspect ratio of each inner crack and distances between adjacent inner cracks. When multiple inner cracks are detected, proximity rules are proposed. But due to the complexity of the problem, it is necessary to verify proposed proximity rules. But experimental study is very difficult due to existence of many parameters, and crack growth occurs inside of the structure. Numerical simulation is needed for this purpose.
This problem is simulated using S-version FEM [2]. Using S-FEM, inner crack is modeled independently from global structure, and crack growth is easily simulated. In maintenance code of nuclear power plant, initial defects are modeled as elliptical cracks in a normal plane to tension loading direction, and growth rate is estimated on this plane. But by using S-FEM, realistic defect shape is modeled, and crack growth by fatigue is simulated. Usually, such small defects are subjected to multi-axial loading, and crack growth behaviors are very complicated. Finally, detect shape becomes elliptical or circular crack in a plane normal to tension loading direction in the structure. Fatigue cycles for these growing processes are calculated, and conservativeness of this maintenance code is discussed. Parametric studies are conducted for this problem, and proximity rules are verified with numerical results.
Health State Monitoring of Bladed Machinery with Crack Growth Detection in BFG Power Plant Using an Active Frequency Shift Spectral Correction Method
