A 2-CRITERIA STATISTICAL-MODEL FOR TRANSITION FRACTURE-TOUGHNESS

A two criteria model is proposed to explain the nature of the fracture toughness scatter in the transition regime for ferritic steels. In th e early part of the transition the model describes the data by a norma l statistical distribution. Here the mean of the distribution is const ant with specimen size and the variance of the distribution varies inv ersely with test specimen size. At a higher temperature, in the middle of the transition, the model results in a Weibull distribution in whi ch both the mean and variance of the distribution vary inversely with change in specimen size. For both of these cases the fracture toughnes s scatterband from one specimen size can be used to predict the scatte rband for another specimen size provided that the thickness constraint is not changed. Between these two regions the model results in a mix of normal and Weibull distributions for which the distribution from on e size cannot presently be used to relate to another specimen size. Th e model is based upon the distribution of the transition fracture toug hness data not on the observed microstructural behaviour; however, it is consistent with microstructural observations. The model does not co mpletely describe all observed data trends; however, it appears to des cribe observed behaviour better than single criterion models.