Anisotropic Ductile Fracture Estimation of Diagonal Cracks in Flange-Shaped Parts

Inclined rotary forming (IRF) combines bending and axial compression with rotation and is employed for forming flange shaft-structured parts from round rod billets. Although the forming load is smaller than the one in conventional processes, cracks may develop during this process. However, it is difficult to predict the onset of cracks using conventional ductile fracture prediction equations. In this paper, an equation for predicting ductile fractures is proposed, which considers anisotropic ductile damage. The proposed equation is expressed as a second-rank tensor resulting from the inner product of the stress tensor and the strain increment tensor. Referring to the previously published results on the compression of cylindrical specimens, the difference between diagonal and longitudinal sidewall cracks was clarified by considering the anisotropy of ductile damage. The proposed equation was then applied to the IRF process, wherein diagonal cracks developed at the outer rim of flange. Consequently, it was possible to estimate the requirements for reducing diagonal cracks by controlling lubrication conditions.