A modified lemaitre ductile fracture criterion and its application to spinning forming

Combining the Lemaitre ductile fracture criterion with finite element simulation is a method widely used in predicting the cracking of a workpiece in plastic forming. In the Lemaitre criterion, the relationship between the damage value and plastic strain is supposed to be linear, which is not the case for some materials that exhibit a nonlinear relationship. In this study, the Lemaitre criterion is modified by substituting linearity for non-linearity between the damage value and plastic strain of a workpiece. The comparisons on the prediction of cone spinning cracks and splitting spinning cracks using the original and modified Lemaitre criteria show that, the prediction of the modified Lemaitre criterion is in better agreement with experiment results. The influences of deviation and mandrel rotation on the distribution and variation of damage value during cone spinning are obtained by the modified Lemaitre criterion. The results show that, the damage value is the smallest and it is most evenly distributed at zero deviation, and the damage occurrence zone under a large negative deviation is different from that under a large positive deviation. For the former, damage mainly occurs in the top zone where large tension stress exists and where there is a contact deformation zone under the action of the rollers, but for the latter damage mainly occurs in the wrinkled flange impacted by rollers. At a given feed ratio, the less the mandrel rotational speed, the slower the damage develops, and the more helpful it is for cone spinning to continue successfully.