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Y. Sumi, Frattura ed Integrità Strutturale, 34 (2015) 42-58; DOI: 10.3221/IGF-ESIS.34.04 56 arrest design. As mentioned, brittle cracks propagating along the welded joint deviate their paths from the weld, and penetrate into the base plate possibly due to the effect of welding residual stress. The arrest toughness, ca K , of a brittle crack in order to prevent the propagation of long brittle cracks was found to be within the range 4,000–6,000N/mm 3/2 at the service temperature, SR147 [30], which were based on the tests of the steel plates with the thickness less than 35mm used for ship structures. Since the thickness of the plates used for extremely large container ships is 50-80mm, investigations have been made by Yamaguchi et al . [36]. For the brittle crack arrest design, certain brittle crack arrest toughness, ca K , must be ensured for a steel plate used for the arrester, so that an efficient test method has been developed to evaluate brittle crack arrest toughness of extremely thick steel plates. The objective of the arrest design of a brittle crack is to arrest brittle crack propagation at specific locations so that a catastrophic failure of the hull structure is prevented in the event of an unexpected crack initiation. For this purpose, the following functional requirements are introduced; 1. brittle crack should be arrested at specific locations (see Fig. 13), 2. hull girder stress after the arrest should be less than the specified yield stress of the applied steel plates, 3. consequently, a brittle crack initiation does not result in large-scale failure of the hull structure. In order to achieve these functional requirements, the following two methods of crack arrest are introduced; Material arrest : to arrange materials of high resistance to brittle crack propagation to arrest brittle cracks, and Structural arrest : to discontinue crack propagation paths by appropriate structural arrangements. Figure 13 : An example of brittle crack arrest in a deck structure. Based on the large-scale crack arrest tests for the determination of minimum brittle crack arrest toughness, it has been found that the toughness 6, 000  ca K  N/mm 3/2 may be an upper limit for crack propagation in the ultra-wide duplex ESSO tests which can evaluate ca K without considering structural discontinuity, Inoue et al . [37]. In order to ensure the crack arrest in the deck plate made of high-arrest steel plate, a minimum shift of butt-weld as illustrated in Fig. 13 has also been recommended. C ONCLUSIONS erturbation analyses of a kinked and curved crack have been reviewed in the present paper focusing attention on the crack path criteria and crack path stability induced by local stress biaxiality or by inhomogeneous fracture toughness. Having reviewed experimental and theoretical studies of brittle crack propagation paths along butt-weld, the concept of fracture control of extremely thick plates of high tensile steel, which are applied to the deck structures of recently developed large container ships, are presented. R EFERENCES [1] Banichuk, N.V., Determination of the form of a curvilinear crack by small parameter technique. Mekhanika Tverdogo Tela, 7-2 (1970) 130–137. (in Russian) [2] Goldstein, R.V., Salganik, R.L., Plane problem of curvilinear cracks in an elastic solid. Mekhanika Tverdogo Tela, 7-3 P