Influence of Stress Factor on Void Closure

Abstract

In the 2nd report, the evaluation factors for void closure under the condition of multipass forging revealed that true strain εz in the z direction is appropriate for the evaluation factors for void closure. However, although the effectiveness of the hydrostatic stress ratio σm /σeq for void closure was clear in the 1st report, the reasons were not clarified. In this paper, we investigated the effects of stress factors on void closure and its handling through numerical experiments. The following results were obtained. 1) By using the true stress in each direction, the deformation behavior of voids can be evaluated as a dimensional change of the diameter on the basis of the frictionless model. 2) In the z stroke direction, the void is easier to close than in the frictionless model when σz /σeq is -1 or less, and harder to close than in the frictionless model if not. 3) The void diameter in the x direction, dx , is smaller than in the frictionless model when σx /σeq is 0 or less, and larger than in the frictionless model if not. 4) When there is a void on the axis of symmetry, σm /σeq can be used to evaluate εz for void closure and the dimensional change of dx . In addition, we clarified the influences of material size, void size, and mechanical properties of the material on void closure.