Constraint issues in cleavage fracture and matters arising from practical application

摘要

In the past 10 years much research has been carried out to deal with the question of how crack-tip constraint effects can be described and, moreover, how crack-tip constraint (stress tri-axiality in the vicinity of the crack tip) contributes to matters arising from practical application of structures and components containing postulated or real cracks and made of ferritic steel. In fracture mechanics, application crack-tip constraint can be influenced by loading (out of plane or multi-axial loading) or by the crack shape and crack depth to ligament ratio. Temperature loading of a crack in a structure is different compared to the loading condition of a fracture toughness specimen and a deep crack behaves differently compared to a short crack. In this paper a model for the prediction of cleavage fracture of ferritic steel is briefly described and summarized and the issues for practical application are pointed out. It turns out that crack-tip constraint, induced either by loading or geometry, can be described quantitatively by local approach models, but there is still a need to understand the micro structural features behind.