A local limit load model for J prediction via the reference stress method

Abstract

A local limit load model is developed for shell/plate type components with surface cracks for determining the local limit load or local reference stress used in J prediction via the reference stress J scheme for defective components. The model is a plate which contains a rectangular surface crack circumscribing the real surface defect and has the same thickness as the component at the crack location. The model is remotely loaded by the primary stresses of the component at the crack location obtained from elastic uncracked-body stress analysis. The global limit load of this model is used as the local limit load of the defective component. The model is validated using 273 cases of 3-D finite element (FE) J results for semi-elliptical surface cracks in plates, cylinders and elbows. The results show that when this local limit load is used in the reference stress J prediction scheme, the predicted J values are reasonably accurate but conservative, compared with the FE J values.