Methods for Complex Cracked Body Finite Element Assessments

Abstract

This paper presents approaches developed to allow consistent best practice assessments for complex 2/3D defects in engineering structures subjected to primary loading and secondary thermal stresses. Methods are outlined and discussed with reference to recent two- and three-dimensional cracked body analyses of components which have been undertaken to determine tolerable defect sizes and inform sub-critical crack growth calculations. The analyses considered a range of postulated semi-elliptical, through-wall and fully circumferential defects in pressure systems. Mixed element type meshing strategies with tied contact in combination with multiple node transformation techniques around the defect front were employed during mesh generation. This facilitated highly refined meshes along the defect front which were required to accurately model extensive plastic deformation in the region of interest. Displacement driven thermal loads required detailed assessment with multiple elasto-plastic material models, since lower bound properties do not necessarily provide the most conservative results. The elasto-plastic J-Integral analyses were shown to provide significant benefit over application of the more conservative Failure Assessment Diagram (FAD) approach. The undertaken assessments were validated against analytical solutions and historic inspection evidence and showed good agreement. In summary the adopted modelling techniques released conservatisms and permitted detailed assessment of complex geometries and load cases.