Issue34

Y. Sumi, Frattura ed Integrità Strutturale, 34 (2015) 42-58; DOI: 10.3221/IGF-ESIS.34.04 42 Focussed on Crack Paths Fracture morphology and its evolution A review on crack path stability and brittle fracture along butt-weld Y. Sumi Yokohama National University, Japan sumi@ynu.ac.jp A BSTRACT . Considerations are made for the fracture morphology and its evolution in relation to the brittle fracture along butt-weld, where crack path stability may play important roles in various aspects. Analyses of a kinked and curved crack are first reviewed in the present paper. Having learned the solutions of a kinked and curved crack, several crack path criteria are compared for the crack path prediction. Then, some aspects of stability of a crack path are examined as to whether it may propagate, keeping its original direction or not in a homogeneous material, and whether crack kinking in a material having inhomogeneous fracture toughness may be predicted by seeking the state which gives rise to an energetically stable one. Having reviewed the morphology of brittle crack propagation along butt-weld, brittle fracture of extremely thick plates of high tensile steel is discussed for the fracture control of recently emerging large container ships. K EYWORDS . Curved crack; Kinked crack; Crack path criteria; Crack path stability; Butt-weld; Extremely thick plate. I NTRODUCTION nalyses of a kinked and curved crack are reviewed in the present paper focusing attention on the brittle crack propagation along butt-weld. The perturbation solutions of a slightly curved crack [1-8] are compared with analytical solutions [9, 10]. Having learned the solutions of a kinked and curved crack, several crack path criteria are compared for the crack path prediction, where criteria may be derived from a stress state prior to the crack propagation [11], the geometrical continuity condition of crack surfaces [1-3], or an energetically favorable condition after crack growth [9]. Then, some aspects of stability of a crack path are examined as to whether it may propagate, keeping its original direction or not in a homogeneous material [12], and whether crack kinking in a material having inhomogeneous fracture toughness may be predicted by energetic stability [7]. Crack path stability in a symmetric homogeneous brittle solid is reviewed [13-15], where the geometry of the body is symmetric with respect to the initial straight-crack line, and where the presence of a small asymmetric loading or slight material inhomogeneity which may produce a small Mode-II stress-intensity factor k II at the original crack tip, leads to non-collinear crack growth. The crack path stability is then examined by taking into account the curved trajectory predicted by the local symmetry criterion [12]. Lastly, having reviewed experimental and theoretical studies of brittle crack propagation paths along butt-weld [7, 16], the concept of fracture control applied to extremely thick plates of high tensile steel is discussed for the structural design of large container ships [17]. A