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The concept of crack arrester, such as the insertion of a high toughness plate, is an effective means to avoid the catastrophic brittle fracture in welded steel structure.Many researches have been made to clarify the arrest behavior of brittle fracture and to establish the arrester design concept, but an inadequacy still exists in the arrest theory.In this study, three types of crack arrest tests, i.e. temperature gradient type double-tension test, stress gradient type double-tension test and surface notched double-tension test were carried out by using mild steel. The data obtained were analyzed from the standpoint of the energy balance concept on the basis of dynamic fracture mechanics.Shear lips which are related to plastic deformation around a propagating crack tip were found to contribute to crack arrestability of steel because they can absorb rather a large amount of energy. And the dynamic fracture toughness KDb corresponding to a brittle fracture surface, which can be evaluated by subtracting the contribution of shear lips from the total absorbed energy, seemed to be defined as a function of crack speed and temperature.Thus, KDb is a material quantity and the arrest behavior of brittle crack may be interpreted generally by this value.Further work to find out the conditions controlling shear lip formation is necessary for the prediction of crack run/arrest phenomenon.

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