構造用低炭素鋼のアコースティック・エミッションとき裂先端の塑性変形

抄録

Acoustic emission during the fracture toughness tests of compact tension specimens of structural low-carbon steel was characterized in terms of crack-tip plasticity and correlated to J integral. The plastic deformation occurred inhomogeneously in the form of Lüders bands. These bands first appeared from the crack tip and propagated circularly. Straight bands were formed from the side edge in the compressive zone in the latter stage of the toughness test. The size of the circular plastic zone near the crack tip was in agreement with the BCS model analysis when the zone was fully constrained.
An abrupt increase in total emission count and a high peak of rms voltage were coincident with the formation of new Lüders bands from the crack tip. The propagation of Lüders bands in other places were not accompanied with large emission. As far as the circular Lüders bands continued to generate from the crack tip, the total count increased proportionally with the size of the plastic zone and the proportional constant was independent of the initial crack length. Thus, two distinct stages were found in the relationship between total count and J integral and the transition point coincided with the point that the Lüders band stopped to formed at the crack tip.