Impact loading and crack arrest
For cracked bodies mechanical phenomena of time-dependent stress-strain fields caused by impact loading and/or crack arrest are described. Relevant crack tip loading parameters are defined and the influence of the loading rate on the material behaviour is discussed (conventional stress-strain curves, brittle-ductile transition, initiation and arrest fracture toughness, dynamic J resistance curves). Suitable experimental techniques are presented to measure crack velocities and crack tip loading parameters, e.g., the shadow optical method. Special problems concerning the testing of ductile pressure vessel steels at elevated temperatures are addressed. The relevance of impact and arrest situations in the context of reactor safety is discussed and ongoing research in this field is briefly summarized.