ASSESSMENT OF THE SIGNIFICANCE OF LBZS IN STEEL USING A PROBABILISTIC MODEL

A probabilistic model of grain coarsened heat affected zones (HAZ), sometimes known as local brittle zones (LBZ), in welded carbon manganese steels is introduced to help explain the apparent discrepancy between deterministic fracture mechanics test results and analyses and structural behaviour. It is shown that for pre- existing cracks in multipass weld HAZs, failure depends on the amount of LBZ that is intersected by the crack front. First order reliability methods and Monte Carlo simulation techniques, incorporating a novel HAZ model and the limit state equation based on the Level 2 assessment procedure in BSI PD 6493: 1991, are used to predict the probability of failure of wide plate tests notched into the HAZ. There was encouraging agreement between the model and experiment. The effect of LBZ height on the probability of failure is illustrated.