A number of deep surface cracks have been detected in components of nuclear power plants in recent years. The depths of these cracks are even greater than the half of crack lengths. When a crack is detected during in-service inspections, methods provided in the ASME Boiler and Pressure Vessel Code Section XI or JSME Rules on Fitness-for-Service for Nuclear Power Plants can be used to assess the structural integrity of cracked components. The solution of the stress intensity factor is very important in the assessment of structural integrity. However, in the current codes, the solutions of the stress intensity factor are provided for semi-elliptical surface cracks with a limitation of a/l ≤ 0.5, where a is the crack depth, and l is the crack length.

In this study, in order to assess the structural integrity in a more rational manner, the solutions of the stress intensity factor were calculated using finite element analysis with quadratic hexahedron elements for deep semi-elliptical surface cracks in plates, and for axial and circumferential semi-elliptical surface cracks in cylinders. The crack dimensions were focused on the range of a/l = 0.5 to 4.0. Solutions were provided at both the deepest and the surface points of the cracks. Furthermore, some of solutions were compared with the available existing studies and with solutions obtained using finite element analysis with quadratic tetrahedral elements and the virtual crack closure-integral method. As the conclusion, it is concluded that the solutions proposed in this paper are applicable in engineering applications.

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