Fracture of metals - Part 1: Cleavage fracture

The structural integrity of any flawed mechanical structure is usually assessed by global and/or local methodologies which can be used under any kind of loading conditions. In this assessment brittle cleavage fracture is the most dangerous fracture mode. Ductile dimple fracture mode is the most common one. This paper only concerned with metallic materials is divided in two parts: the first one is devoted to cleavage fracture and the second one to ductile fracture. In this first paper the main characteristics of cleavage fracture in metals and alloys, in particular in BCC steels, including scatter, size effect, shallow crack effect, are firstly reviewed in the light of a conventional global approach based on fracture mechanics (K, J). Then in the second part of the paper, a number of attempts made to account for the loss of constraint effect with large scale yielding, by using a second parameter (T, Q) in addition to K(J) parameter are briefly mentioned. The third part of the paper is devoted to a review of cleavage micromechanisms and to the application of the local approach to cleavage fracture. The Weibull weakest link hypothesis is shown to account reasonably well for a number of the characteristics associated with cleavage fracture. Applications of the theory to a number of results obtained on laboratory specimens and on large components are shown.