• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.2
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• pp.275-282
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• 2001

The reactor pressure vessel is usually cladded with stainless steel to prevent corrosion and radiation embrittlement. Number of subclad cracks may be found during an in-service-inspection due to the presence of cladding. It is specified, in ASME Sec. XI, that a subclad crack is characterized as a surface crack when the thickness of the clad is less than 40% of the crack depth. This condition is provided to keep the crack integrity evaluation conservative. In order to refine the fracture assessment procedures for such subclad cracks under a pressurized thermal shock condition, three dimensional finite element analyses are applied for various subclad cracks existing under cladding. A total of 36 crack geometries are analyzed, and the results are compared with those for surface cracks. The resulting stress intensity factors for subclad cracks are 6 to 44% less than those for surface cracks. It is proven that the flaw characterization condition as specified in ASME Sec. XI can be overly conservative for some subclad cracks.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.22 no.4
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• pp.779-789
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• 1998

In this paper, the thermal shock responses of collinear cracks in a layered medium are investigated based on the uncoupled, quasi-static plane thermoelasticity. The medium is modeled as a bonded structure composed of a surface layer and a semi-infinite substrate. Between these two dissimilar homogeneous constituents, a functionally graded interfacial zone exists with the nonhomogeneous features of continuously varying thermoelastic properties. Three cracks are assumed to be present in the layered medium, one in each one of the constituent materials, aligned collinearly normal to the nominal interfaces. A system of singular integral equations is solved, subjected to the forcing terms of equivalent transient thermal tractions acting on the locations of cracks via superposition. Main results presented are the transient thermal stress intensity factors to illustrate the parametric effects of various geometric and amterial combinations of the medium with the thermoelastically graded interfacial zone and the collinear cracks.