An engineering method for constraint based fracture assessment of welded structural components with surface cracks

In this study it has been shown that accurate descriptions of crack-tip str ess-fields in surface cracked welded plates can be obtained without large 3 D FEA models. When a fracture mechanics FE analysis is required in a large construction, existing shell models can be used in combination with a plane strain submodel. The 2D plane strain model is driven by displacements from the global shell model. This technique has been used to simulate crack-tip stress-fields in a surface cracked plate. The crack-tip stress fields are characterised with the J-integral and the constraint parameter, Q. The crac k in the global shell model was simulated with line-spring elements. The gl obal behaviour as well as the crack-tip stress-fields of the plane strain s ubmodel have been compared to a 3D solid model. Initially, the crack-tip st ress-fields in the plane strain model and the 3D model with surface crack w ere compared, using the same inplane mesh and element type. It was found th at when first order elements were used, the constraint was higher in 3D tha n in plane strain. For second order elements, however, the trend was the op posite. By using a correction factor for the load, the load vs. J behaviour and the crack-tip stress-fields of a surface cracked plate can be predicte d from a shell analysis with line-spring elements and a plane strain model. Accurate predictions of J and Q were obtained using the shell + submodel t echnique for homogeneous material and for a weldment with fusion line crack . The shell + submodelling technique was used to assess brittle fracture in two steel weldments with a surface crack using the RKR failure criterion b y Ritchie et al. [16]. For the investigated case, the toughness requirement s could be relaxed significantly based on the two parameter analysis compar ed to conventional fracture mechanics analyses. (C) 1999 Elsevier Science L td. All rights reserved.