大規模降伏脆性破壊強度に及ぼす板厚の影響について

概要

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In this paper, the effects of plate thickness on brittle fracture of mild steel (SS 41) accompanied by large scale plastic deformation ahead of the crack tip were examined for three point bend specimens. These specimens were four kinds of size completely satisfied all aspects of British Standard DD 19 for COD Testing. The loads versus crack opening displacements V_g at the notch mouth were obtained for each of the specimens at the temperatures ranging from room temperature to -150℃, and the crack tip opening displacements Φ_o Were directly measured from specimens by means of silicon rubber casting method at room temperature. In addition the authors proposed the value β as the constraint coefficient due to plate thick-ness, and incorporated it into Finite Element Method program. As a result of this study, the following conclusion were obtained: (1) The estimated fracture stresses obtained by FEM calculation considering β showed fairly agreement with experimental results. ( 2 ) The fracture phenomena of thick plate containing a crack of SS 41 are ductile from room temperature to -50, and fibrous crack initiation is independent of plate thickness and temperature, but the thickness of plate has extensive influence on brittle fracture toughness at lower temperature than -50.