材料
Online ISSN : 1880-7488
Print ISSN : 0514-5163
ISSN-L : 0514-5163
低強度鋼における延性破壊の発生に及ぼす応力三軸度の影響
大塚 昭夫宮田 隆司西村 誠二木村 雅保馬渕 宗人
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1980 年 29 巻 322 号 p. 717-723

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Tensile Tests on circumferentially notched round bar tensile specimens with notches of various acuity have been made on SS41 and SM50C in order to clarify the effect of stress triaxiality on ductile fracture initiation. Tests on tensile and bend specimens with a slit or fatigue cracks have also been made in order to obtain the relation between the fracture toughness and the condition of ductile fracture initiation.
The plastic strain at the ductile crack initiation decreased sharply with increase of stress triaxiality in the range where σm/σ (σm: mean stress, σ: effective stress) is smaller than about 1.2, but it became almost constant for larger σm/σ than 1.2. A similar dependence on stress triaxiality σm/σ was observed in the dimple size distribution on the fracture surface.
The fact that the crack tip opening displacement at fibrous crack initiation is almost independent of various factors, such as specimen thickness, crack depth, loading mode and so on, may be explained by this stress triaxiality dependence of ductile fracture initiation, because the value of the stress triaxiality σm/σ around the crack tip is larger than about 1.2 regardless of the factors above mentioned.

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