Prediction The Forming Limit Of Ni Coated Sheet By Ductile Fracture Criterion

With the developing of science and technology, the coating materials are widelyused. Electro-deposition of nickel coated steel is used for the battery. It is widely usedbecause of it can be first electroplated and then stamping. Due to the existing ductilefracture criterion is basically limit for prediction the forming limit of single-layersheet. However, the study of prediction of multi-layers sheets, such as theelectrodeposited nickel coating sheet, has not started. So this paper study using theductile fracture criterion to predict the forming limit of nickel coating sheet during thestamping period. To solve this problem, we conduct a deeply study, the researchcontents are as follows:(1) In order to get the basic parameters of nickel coating sheet, the low carbonsteel sheets and Ni sheets are processed to a certain shape. And then a tensile test istaken under the universal testing machine. The basic parameters of the low carbonsteel sheet and the Ni sheet are obtained from the tentile test. And the break strain oflow carbon steel sheet and the Ni sheet are0.764and0.687.(2) In order to derivate a new ductile fracture criterion for the electrodepositednickel coating sheet. The existing ductile fracture criterions are used to evaluate theforming limit of nickel coating sheet. The material constant should be determinedbefore forecasting the forming limit. Calculating the material constant of existingductile fracture criterion, and make use of the coefficient of variation and sample biasto evaluate the material constant. So the more accurate criterion is found. The mainreasons that affect the forming limit of nickel coating sheet are got.(3) Base on the damage mechanics. Using the Hill equivalent stress instead ofMises equivalent to describe the punch processing which consider the thickanisotropic, and the new criterion can derivate by. The coefficient of variation andsample bias are smaller than the existing criterion. It explained that the new criterionis more accurate than the existing criterion.(4) Use the finite element software to simulate the punch process of nickelcoating sheet. The stresses and stains of each time can get during the processing.Putting the stresses and strains into the new criterion and forecasting the forming limit.The result of criterion calculation and experiment is similar. It verified that theaccurate of new criterion.