MICROMECHANICAL ASPECTS OF CONSTRAINT EFFECT AT BRITTLE FRACTURE INITIATION

摘要

Applying the two-parameter fracture mechanics approach to the analysis of failure initiation condition of the three point bend specimens with shallow and deep cracks were tested at various temperatures. Low carbon manganese cast steel was used for the analysis. This steel is tested as one of several candidate materials for containers of spent nuclear fuel. The effect of crack length on the fracture toughness-temperature diagram has been analysed. Although a strong dependence of measured fracture toughness on crack tip constraint was observed no evident differences in fracture morphology have been identified except for quantitative ones. Peculiarities of fracture behaviour in the transition and lower shelf regions of the steel investigated have been explained. The effect of crack tip constraint on brittle fracture characteristics has been quantified by means of the Q-parameter. The role of critical (cleavage) fracture stress in brittle fracture initiation under the influence of crack tip constraint has been analysed.