高力アルミニウム合金の延性破壊に及ぼす応力三軸度の影響と破壊じん性における拘束効果

Abstract

Constraint effect on the ductility and the fracture toughness of Al-alloys were investigated to examine a modelling of the fracture toughness and to confirm the applicability of unique parameter fracture mechanics to the mircovoid coalescence type of fracture. Stress triaxiality effect on the ductility was investigated in notched round bar specimens. Toughness testing was performed for three points bend and CT specimens with different thickness and notch depth ratio. Stress triaxiality effect on the ductility is significant in low strength materials. The fracture toughness, JIC of high strength Al-alloys, 7075-T6 is varied with the specimen thickness even in the specimens that satisfies the prescription on the size requirements for plane strain condition in the toughness testing method, ASTM E1820. Morphology of the fracture surface composed with the dimple pattern and the intergranular fracture is closely related to the degradation in the toughness. Correlation between the toughness and the ductility in notched specimens demonstrates the validity of the characteristic distance model that describes the toughness in terms of the flow stress and the ductility of the materials.