The non-conservatism of the Weibull function when applied to the statistics of fracture toughness

It has become very clear that in many cases fracture toughness for a given material is variable; for example a quenched and tempered, high-strength low-alloyed steel such as might be used for the construction of pressure vessels for nuclear-power plants or off-shore platforms. Indeed for these materials fracture toughness can no longer be looked upon as a single- valued property at any given temperature but must rather be seen as a property with an inherent distribution of its values. The present paper shows that recent models for the distribution of toughness which are based on the two-parameter Weibull function are potentially dangerously nonconservative both for the estimation of low and medium values of toughness and for the estimation of the sizes of defects present in proof- tested parts. (Author)