Fracture Prediction In Incremental Sheet Forming Based On Ductile Fracture Criterion

Compared with the traditional sheet forming process,metal sheet incremental forming technology has many advantages,such as short cycle time,low cost,easy operation.And it has significant advantages in product customization,diversification and sample trial.As the characteristics of "local compression,point by point forming",the forming limit of sheet in incremental sheet forming will be higher than that of traditional stamping process.the forming process of the sheet forming process will be significantly higher than the traditional stamping process.However,when the forming angle of the part is larger than critical value,the thickness of the sheet becomes more and more serious,which leads to the failure of the parts to be used and even the fracture of the material.Therefore,it is of great importance to find a method to predict the fracture condition suitable for progressive forming process.However,at present,the commonly used methods to predict the fracture of sheet metal forming are strongly dependent on the strain path,and can't achieve constant prediction.Based on the successful application of Oyane ductile fracture criterion in the prediction of plastic deformation of traditional sheet,Oyane criterion was introduced into the sheet metal forming process.Then,the fracture of DC56 D + Z steel plate was predicted by secondary development of ABAQUS software.Finally,The influence of process parameters on the fracture was discussed.The main research contents and results are as follows:?Determine material parameters by tensile test.The DC56D+Z steel plate with thickness of 0.8mm was taken as the research object.And the material parameters C,C1,the constitutive equation of the material and other mechanical properties of the Oyane ductile fracture criterion were determined by the uniaxial tensile test at room temperature and the plane strain tensile test.?Write VUMAT subroutine and verify its correctness.Using ABAQUS finite element software material subroutine interface,the Oyane toughness criterion is written into the VUMAT material subroutine.Then the accuracy of the Oyane model subroutine is determined by the establishment of the finite element model of room temperature tensile.In addition,the Oyane model and Von Mises model are used to simulate the incremental forming process.It is proved that the model can effectively analyze the sheet metal forming process.?Determine the critical conditions for sheet metal fracture.Using the I value of fracture integral in Oyane criterion as the fracture quota and based on the incremental forming experiment and finite element analysis,the critical value of the fracture integral value I=4 is a critical condition to judge whether the material is broken in the sheet metal forming process.If the calculation shows that I <4,It can be concluded that the sheet metal can be formed smoothly under the condition of the processing.Otherwise,the plate will rupture.?Establish a numerical model for predicting the maximum rupture integral I value by using response surface method.Otherwise,the sheet will break down.In order to avoid the defects of forming,the influence of process parameters on the maximum rupture integral value is further analyzed.It is found that the maximum rupture I value increases with the forming angle(?),the interlayer spacing(?z)and the tool head diameter(d).The influence of the process parameters is gradually weakened.In addition,the influence of the maximum I value of the parameter interaction is analyzed,and it is found that the combination of ?& ?z,? & d have a great influence.In addition,through the optimization of numerical model,the layer spacing ?z = 0.1mm,the tool head diameter d = 5mm was determined the optimal parameter for the forming straight wall parts.Finally,the superiority of this set of parameters is determined by finite element analysis and experiment.