Determination of Fracture Toughness for Thin Section Specimens with Optimized Finite Element Mesh

Abstract

An analytical approach is developed to pre dict load verses crack advancement for thin section center cracked specimens under tensile monotonic load . The predicted failure load and the crack length at the onset of crack instability are used to calculate the fracture toughness of the material. The l oad history verses the crack growth is also used to determine the material crack resistance curve ( K-R curve). The methodology presented here consist s of modeling of the center cracked specimen using finite element method to predict the crack tip stress st rain fie ld under the mode I load ing and incorporating the results of the finite element analysis to the progressive failure analysis code GENOA (General Optimization Analysis ) to perform crack propagation analysis. This approach is iterative and at each st age of the analysis the crack specimen model will be updated to account for stable crack propagation by material degradation at the crack tip and the subsequent stiffness reduction and removal of the damaged elements as the load magnitude increases . The fi nal failure load and the crack length are highly dependent on the initial finite element meshing of the crack tip. Therefore , an approach based on the linear elastic fracture mechanics (LEFM) theory is presented to optimize the crack tip mesh. Published te st data for a number of metallic ce nter cracked specimens were compared with the analytical results to validate the analytical approach presented in this paper.