Nonlinear Fracture Mechanics Analysis Considering Material Inhomogeneity of Welded Joints

Professor Hiroshi Okada and his team from the Department of Mechanical Engineering, Faculty of Science and Technology, Tokyo University of Science, Japan, are engaged in the field of computational fracture mechanics. This is an area of computational engineering that refers to the creation of numerical methods to approximate the crack evolutions predicted by new classes of fracture mechanics models. For many years, it has been used to determine stress intensity factors and, more recently, has expanded into the simulation of crack nucleation and propagation. In their work, the researchers are proposing new methods for fracture mechanics analysis and solid mechanics analysis.

Effects of Flaw Shape (Idealization) on the Interaction of Co-Planar Surface Flaws

Engineering Critical Assessment (ECA) guidelines contain amongst others, rules to assess flaw interaction. Major flaw dimensions (depth or height and length) are typically characterized assuming the flaws to be contained entirely within a bounding rectangle through a procedure known as flaw idealization. In (computational) fracture mechanics based calculations, flaws are often assumed to be (semi-)elliptical. This paper investigates the interaction between identical co-planar surface breaking flaws. Two flaw shapes are considered and compared: “canoe-shaped” (quarter-circular ends and constant depth elsewhere) and semi-elliptical. Especially for long shallow flaws, the canoe-shaped approximates the bounding rectangle, whereas the semi-elliptical shape only touches the bounding rectangle at three points (deepest point and two points at the surface). Several flaw dimensions and spacing distances are studied through an extensive parametric study comprising elastic and elastic-plastic finite element simulations. The results, based on Stress Intensity Factor (SIF) and J-integral analysis, show how the flaw shape can affect the degree of interaction. Notably, the inconsistency is less in linear-elastic analysis, but becomes more pronounced at higher (elastic-plastic) loading levels. This work highlights a challenge of comparing analytical and numerical based evaluations of interaction with ECA guidelines.