The American Society of Mechanical Engineers (ASME) KIc curve is a function of test temperature (T) normalized to a reference nil-ductility temperature, RTNDT, namely, T – RTNDT. It was constructed as the lower boundary to the available KIc database. Being a lower bound to the unique but limited database, the ASME KIc curve concept does not discuss probability matters. However, a continuing evolution of fracture mechanics advances has led to employment of the Weibull distribution function to model the scatter of fracture toughness values in the transition range. The Weibull statistic/master curve approach was applied to analyze the current ASME KIc database. It is shown that the Weibull distribution function models the scatter in KIc data from different materials very well, while the temperature dependence is described by the master curve. Probabilistic-based tolerance-bound curves are suggested to describe lower-bound KIc values.

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