Numerical Simulation Study On Forming Limit Of Hot-rolled Pickling Sheet

The forming limit diagram is an important criterion to evaluate the forming ability of the sheet.The accurate forming limit diagram of sheet can assess pickling sheet metal forming ability effectively and provide scientific theoretical basis for the actual production process.In this paper,the forming limit diagram of pickling sheet was obtained by hemispherical punch tests.The ABAQUS finite element analysis software was also used to analyze the forming performance of sheet metal.On the one hand,from the macroscopic plasticity theory,the historical principal strain of the finite element numerical simulation results of the sheet metal are analyzed by the maximum second-order principal strain criterion and the Savitzky-Golay smoothing principle.The principal strain and the minor strain of the forming limit curve were determined when the second order principal strain reached its maximum value.On the other hand,from the meso-damage theory,the criteria of critical necking void volume fraction fc and fracture void volume fraction fF were proposed to predict the forming limit diagram of the pickling sheet based on the GTN damage model.The numerical results were compared with the experimental data and the factors influencing the forming limit diagram were analyzed.The results showed that:(1)the forming limit curve obtained by the maximum second-order principal strain criterion was in good agreement with the experimental results,but slightly lower than the experimental results.The reason for the error was that the limit strain point in the experiment was determined after the necking of the specimen,and the numerical simulation result was based on the strain value of the material at the time of necking.(2)Compared with the forming limit curve obtain by the fracture volume fraction fF in the GTN damage model,the FLC acquired by the void volume fraction fc was much closer to the experimental results.The forming limit curve obtain by the fracture volume fraction fF was higher than the experimental result,and could be used as the upper limit of the forming limit diagram.(3)The influence of the thickness of the sheet on the forming limit diagram is small,but the friction condition has a great influenced,and the forming limit curve decreases significantly with the increase of the friction coefficient.