Application of the Local Approach to Cleavage Fracture to Failure Predictions of Heat Affected Zones

Abstract

With the increased capabilities of elastic-plastic finite element analyses and hence the possibilities to determine accurately the stress distribution ahead of sharp cracks the use of fracture risk predictions based on a local fracture parameter has recently attracted much interest. To date most investigations in this area concentrated on homogeneous materials avoiding the complications related to the complex situation of welded joints. In this paper results are presented where the Local Approach to cleavage fracture has been applied to the heat affected zone of two structural steel welds. Local cleavage fracture parameters were determined from tests and finite element modelling of notched tensile specimens. In all cases he properties of the weld metal, the parent material and the heat affected zone (HAZ) were determined. A thermal simulation technique was used to produce large enough areas of HAZ microstructures for tensile and notched tensile testing. Subsequent application of the Local Approach to the crack tip situation for the prediction of the dependence of fracture toughness on temperature and the scatter in fracture toughness only produced satisfactory results for a limited number of the situations modelled. Discrepancies between predictions and actual results are thought to be due partly to the differences in FE mesh and stress distribution between notched tensile and pre-cracked bend specimens.