A New Damage Evolution Model for Cold Forging of Bearing Steel-Balls

As ductile damage has a severe impact on the performance of bearing steel-balls (BSB), it is necessary to apply the ductile damage evolution model for predicting the distribution of ductile damage in BSB. A new ductile damage model was developed using physically-based internal state variables method by considering the effect of two important stress state parameters: stress triaxiality and relative ratio of max principal tension stress, on the ductile damage evolution. The newly developed ductile damage model was implemented into the commercial FE code, DEFORM-3D, via a user defined subroutine and cold forging simulation was operated. BSB formation tests were carried out and the microstructure and micro-damage were examined from the tested samples. FE simulation results of ductile damage were compared with those of tested samples. Good agreements have been achieved, which proves that the newly developed ductile damage model enables micro-damage evolution during cold forging to be well predicted. Some constructive suggestions have been obtained to improve the quality of BSB during cold forging.