A new forming-limit criterion for fracture prediction in a powder forging application

This research investigates the forging limit of sintered compacts by taking into particular consideration the effects of void evolution in the process. A new fracture criterion for a porous medium, which is based on the first principal strain energy density (FPSED), is developed as well. The experiment and the finite element analysis (FEA) have been conducted to examine the process. The material properties of porous compacts are measured by both the uni-axial tension and the compression tests. The finite element model is first verified with the upsetting experiment under different frictional conditions. By applying this new criterion, the fracture upsetting simulation demonstrates much better accuracy than the results derived from the equations proposed by other researchers. The fracture prediction in forging the gear blank is also presented as a practical application to reinforce the reliability of this model. Besides the degradation of the strength, this study specifically shows that voids in the sintered preform exponentially reduce the forging limit.