Experimental Study And Finite Element Analysis On Time-Dependent Springback Of Metal Sheets Under Deforming

Metal sheets are widely used in the aerospace,aircraft manufacturing,automotive cover molding areas,and now the automotive lightweight is a trend,which is inseparable from the metal sheets forming.The metal sheets forming has defects such as wrinkling,rupture and springback.Springback has a great influence on the metal forming performance,so it is need to solve the problem as soon as possible.In recent years,the study found that with unloading after deformation of metal sheets,there is not only instantaneous springback phenomenon due to elastic deformation,but also a time-dependent springback phenomenon.Based on the theory of elastic plasticity and the theory of visco elasticity,the mechanical properties of the material were obtained by the uniaxial tensile test.The results can provide reference for the follow-up time-dependent springback test and finite element simulation.The main research contents are as follows:(1)The time-dependent springback of AC170 is the highest,DP600 is the second,and TC4 time-dependent springback is the smallest.At the same time,the uniaxial tensile and three-point bending time-dependent springback tests along 0 °,45 ° and 90 °directions with repect to the rolling direction were carried out,and the time-dependent springback and the anisotropy coefficient showed exponential regularity changes in data processing and analysis.(2)Based on the room temperature creep test of DP600 and AC170,the stress relaxation curves of two materials were fitted to the Prony series,and the Wiechert viscoelastic model was built.With the material parameters of each model determined,the model parameters were provided for the finite element simulation.The parameters of the anisotropy coefficient are added to the material definition of the finite element simulation,which is used to simulate the time-dependent springback phenomenon of the sheets.The result is closer to the experimental result.(3)For the three-point bending test finite element simulation,by analyzing the simulation results of the stress distribution of,it is found that the stress gradually reduced from the end time of deformation to the instantaneous springback time and then to the timedependent springback time,and it is concluded that the time-dependent springback is driven by the residual stress.(4)To investigate the stress and strain distribution and shape of the fracture in the instability process of the tubes under uniaxial tension load,finite element analysis for whole process of uniaxial tension for the tube was carried out based on a series of experiments on axial tensile of 1Cr18Ni9 Ti tube.The finite element method was used to simulate the stressstrain distribution and the shape of the fracture in the whole process,which provided a reference for the analysis of mechanical properties and formability.