Elastic-Plastic Analysis of Surface Crack in Round Bars under Torsion

An elastic-plastic finite element analysis (FEA) is used to determine the J-integral around the crack front of 3-dimensional semi-elliptical surface crack in a round bar under torsion loading. Crack geometries are based on the experimental observation. The present model is validated using the SIF under bending loading since no suitable SIF for torsion is available. Lack of numerical solution of elastic and plastic stress parameters under torsion are found. The FE J values are normalized by dividing with the estimation J value using a reference stress method. It is found that higher J values are obtained for deep cracks and the maximum J changed from the deepest point along the crack front to the outer point at the free surface when a/D > 0.2. J values can be estimated for all type of crack geometries under consideration with a correction factor, h(1).