30 破壊力学的考察によるシャルピー衝撃試験とCTOD破壊靭性試験の遷移温度差予測手法の提案

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This paper presents a method for predicting the CTOD fracture toughness transition temperature T^<CTOD>_i for structural steels from Charpy impact toughness T^<Charpy>_i. T^<CTOD>_i and T^<Charpy>_i are defined as the temperature at which brittle fracture coincides with ductile cracking in both Charpy and CTOD testing. This method is proposed based on "local plastic strain criterion" for ductile crack initiation and "Weibull stress criterion" for brittle fracture initiation. The validity of this method is investigated for 490MPa class strength steel; T^<CTOD>_i predicted in accordance with proposed method is almost consistent with that measured in experiment. For industrial applications, an engineering formula is established for predicting the transition temperature difference ΔT_i=T^<Charpy>_i-T^<CTOD>_i from Charpy impact test for structural steels with yield strength from 300MPa to 900MPa. In this formula,ΔT_i is dependent on the material properties that are the ductility level (ε^^-^<tip>_p)_i and Charpy impact toughness level T^<Charpy>_i and flow properties (yield stress σ_Y and 2% Mises stress). The applicability of this formula is verified for 490MPa, 590MPa, and 780MPa strength class structural steels.
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