The Bauschinger Effect In Auto-body Forming And Its Influence On Springback

Strain hardening of mental in one direction reduces the yield stress in theopposite direction, the existence of Bauschinger effect plays a unique role on theaccuracy of the sheet metal forming simulation. Especially now extensive use of highstrength steels and aluminum alloys, makes springback phenomenon an increasinglyimportant issue, the accuracy of the finite element springback prediction is alsobecoming improve. In order to improve the prediction accuracy of springback it isnecessary to study the Bauschinger effect of materials.The research of Bauschinger effect on sheet metals materials has always been aproblem in academic circles, which result from sheet material under the compressionstate is instability and circular bending test can’t research the Bauschinger effect withaccurate greater strain. Such a device is designed and manufactured to avoid bendingof specimen in the compression process. With the device tension-compression testswere carried out and the stress-strain relationship in different pretension strain wereobtained, and the parameters of Bauschinger effect were calculated. The phenomenonof Bauschinger effect, such as the rounding of the reverse flow curve, yielding at lowreverse stresses and permanent softening were discussed.The material model parameters, which can describe the Bauschinger effect, isobtained by comparing the experiment results with simulation results. U-channelforming test of DC06and DP600was carried out. The influence of different materialmodels, which include the hardening laws of isotropic hardening, Isotropic-kinematichardening and kinematic hardening, on springback prediction was analyzed bycomparing the simulation results. The effects on the precision of springbackcalculation were discussed theoretically.Finally, in order to study the influence of cycle bending on springback, a set offree bending tool was designed. Three set of bending tests of sheet steels (DC06andDP600) were conducted. The experimental results were compared and analyzed by asimplified model to show the influence of Bauschinger effect on springback.