抄録
The out-of-plane strain constraint around a notch/crack tip of a round bar with a deep circumferential notch/crack is as high as that of a plane-strain compact tension specimen (CT). Especially a round bar with a circumferential crack also shows equivalent Mode 1 stress distribution with a CT because of narrow ligament area equi-axis voids followed by cleavage fracture, caused by tri axis stresses, are generated limited at 0.5 < r/(J/σ_0) < 1.5. On the other hard, that with a circumferential notch (tip radius=0.05mm) shows smaller Mode I stress distribution, and shear elongated voids, caused by low in-plane strain constraint a generated. The voids are widely located at 0.5 < r/(J/σ_0) < 3. Although the obtained critical J by a specimen with a deep circumferential notch may not be so overestimated one, the fracture mechanism is different from that with a deep circumferential crack.
