2019 年 60 巻 703 号 p. 221-227
Product defects have been predicted by numerical simulations in cold forging. Various ductile fracture prediction equations have been proposed, some of which have already been implemented in commercial finite element codes. However, there are still some cases where the fractured region of actual products cannot be predicted using the existing ductile fracture prediction equations. In the present paper, a new equation for predicting ductile fracture was proposed, which can improve the prediction accuracy of ductile fracture was proposed. The proposed equation was expressed as a second-rank symmetric tensor, which is a product of the stress tensor and strain increment tensor. The effectiveness of the proposed equation was confirmed in a uniaxial tension test of a notched round bar. Next, the proposed equation was applied to the cold forging of a hollow shaft. As a result, the calculated most-damaged region was corresponded to the actual fractured region of the product.