高強度鋼における破壊靱性値の板厚依存性

概要

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The effect of specimen thickness B on the fracture toughness K_C as well as on the shear lip thickness B_<SL> of high strength steels was examined to obtain new models for explaining the thickness dependency of K_C, and the influence of tensile properties on the dependency was studied. The results obtained are as follows. (1) For each steel, K_C increases with the increase of B in a smaller thickness range where slant fractures occur. In the middle thickness range, however, where fractures of a slant-flat mix mode occur, K_C decreases with the increase of B, and in a larger thickness range where flat fractures predominate, K_C gradually decreases to a constant value (plane strain fracture toughness K_<IC>). (2) The shear lip thickness B_<SL> decreases with the increase of specimen thickness B in the range of the mix mode fracture. (3) The new models proposed in this study can express the thickness dependency of K_C relatively well. (4) An approximate relation, B_<SL>/B=αβ^m_c holds between B_<SL>/B and the relative plastic zone size β_C (=K^2_c/Bσ^2_<ys>, where σ_<ys> is yield strength). The exponent m does not much change with materials (m=0.6∿1.0), but the coefficient α is dependent on the work hardening exponent n (α≒0.0016/n^1.6).
社団法人日本鉄鋼協会の論文
1976-10-01