Probability estimation for the assessment of environmental effects on fracture toughness

Over-conservations in deterministic assessments of structural safety can be reduced on the basis of the quantification of the uncertainties in the assessment methodology in the form of probability values. Of particular importance is the prediction of fracture toughness after changes due to time-dependent degradation during operation. This is a multi-stage process for which the combination of uncertainties requires probability values defining the uncertainty at each stage. The analysis strategy and techniques described in this paper have general application in the determination of probability estimates for predicted properties of ageing materials. The approach is illustrated in the specific application to the prediction of fracture toughness in the ductile-to-brittle transition region for irradiated material from start-of-life (SOL) fracture toughness data and irradiated Charpy impact energy data.