FEM and Experimental Evaluation of J-Integral for Multi-phased Materials

The integrity of any structure is very important so that it does not fail during its service life. Accordingly,it is of paramount importance that the integrity of complicated structures such as nuclear power plant, aircrafts, ships, submarines etc. is not compromised. Weldment is more likely to contain inherent flaws or micro-crack which may later propagate from weld metal to the base metal under high stress conditions. Although J-integral is a well established parameter to determine the fracture when the crack tip plasticity is considered, but it only holds good when the crack growth takes place in a homogeneous medium. In case of multi-phase materials such as weldment, there is no methodology to calculate the J-integral experimentally. Therefore, a modified J-integral is proposed earlier to calculate J numerically for multi-phase materials, but it has never been validated experimentally. An expression to calculate J integral for a compact tension (CT) specimen, welded transverse to the direction of crack growth from experimental load-displacement data is proposed. Finite Element (FE) analysis is carried out to calculate J values, employing modified J-integral for welded CT specimen. Furthermore, the effect of a/W ratio and HAZ on the fracture toughness of a welded compact tension is also studied. Scanning Electron Microscopy is carried out to understand the fracture behaviour of the materials.