COMPUTATIONAL FRACTURE MECHANICS ASSESSMENT OF 3-D CRACK-LIKE DEFECTS IN COMPLEX GEOMETRIES

The application of a fracture mechanics based methodology for integrity assessment of complex structural components containing flaws often requires computational simulation where the flaws have to be modeled explicitly due to the absence of the appropriate analytical solutions. Moreover, for large flaws, re-distribution of loads may occur and therefore for an accurate assessment the flaw needs to be embedded within the structural model. A critical issue that must be addressed in a three-dimensional finite element simulation of a structural component containing a crack-like defect is that of mesh generation. In this paper, an efficient methodology has been developed based on the use of general purpose finite element packages and other commercial software to automatically generate the meshes. The model reflects the full complexity of a 3-D structure ensuring at the same time the required mesh resolution around the crack front for the determination of parameters used in fracture mechanics assessment. The approach is demonstrated through computational simulations of a tubular K-joint containing a crack-like defect with elastic and elastic-plastic material properties. From these analyses, the parameters required for construction of a geometry-dependent and material-specific failure assessment diagram (FAD) are derived. Results of the fully computational fracture mechanics assessment are compared with those generated in accordance with Annexes B and P of BS 7910:2005. It is demonstrated that the level of conservatism in fracture integrity assessment of tubular joints can be reduced if the crack driving force is determined directly from the computational analysis of the cracked geometry. A discussion on the application of different limit load and reference stress solutions is presented and the importance of the appropriate selection of the limit load solution is highlighted.