Cleavage fracture assessment of transient thermo-mechanical loading situations by local approach

Brittle failure of any nuclear component due to instable propagation of a postulated crack needs to be excluded, and assessed reliably. Currently, cleavage fracture for complex transient loading situations with decreasing temperature and increasing load is analyzed based on isothermal fracture toughness curves with large conservatisms. In this study these transient loading situations were studied experimentally by testing different specimen types (stress conditions) with varying slopes of load versus temperature, and different pre-loads. A probabilistic local approach concept which considers local stress and strain developments, as well as load history, was used to numerically assess cleavage fracture. In all cases the model was able to quantify the fracture probability excellently in a slightly conservative manner. The strong over-conservatism of the Master Curve concept for transient loading was reduced to a tolerable minimum.