The role of pure shear strain on the site of crack initiation in notches

Abstract

The states of stress and strain at the root of V and U-notches were examined through the use of an elastic-plastic finite element computer program in an effort to develop a criterion for predicting the site of crack initiation. Using simple bending under conditions approximating plane stress, the sites of initiation were determined experimentally to be well removed from the notch centerline. Furthermore, the paths of crack propagation followed the directions of pure shear strain,i.e. the “characteristic” directions. The slip line fields,i.e. the directions of pure shear strain, produced from the results of the finite element program agreed well with results expected from classical plasticity solutions. Examinations of numerous stress and strain quantities along and between the slip lines were conducted in an effort to evolve a selectivity rule that could be used to predict along which slip line a velocity discontinuity would be activated to form a crack. A rapid decrease in the average value of pure shear strain along the contour of the notch near the initiation site provided the sought predictive capability.