延性破壊の塑性力学的予測 : 第2報, 規準の適用性

概要

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In 1st Report the criterion of load instability was introduced for assessing the onset of ductile fracture. So far the multiplicity of deformation has been considered to occur at plastic instability. The concept of plastic instability is based on the possibility of multiplicity in deformation rate under an identical boundary condition. However, plastic instability does not assure the coexistence of unloading with continuous plastic loading. Therefore, it does not bring the onset of necking. On the other hand, load instability provides the possibility of coexistence with unloading as long as it occurs after plastic instability. Then, we adopt load instability as a tool for examining ductility. It is very interesting whether the prediction based on the mechanics of plasticity has the ability of evaluation for the effect of hydrostatic pressure upon ductility. Other interest is central bursting in extrusion or drawing, surface ductility in upsetting, the difference of formability between cylinder bulging and sheet stretching, and so on. Their ductility is evaluated associating load instability with plastic instability.
2001-07-25