Research And Application Of Key Technology Of Dynamic Adaptive Analysis Based On Sheet Metal Forming

In the process of sheet metal forming,there are three nonlinearities of geometry,material and contact,and large deformation,large displacement and large rotation are accompanied.In the finite element dynamic simulation analysis,it is difficult to accurately analyze the area where the local field variables change drastically by using the coarse grid,resulting in low analysis accuracy.The use of refined grids can effectively improve the analysis accuracy,but it will increase the computational cost and reduce the analysis efficiency.Therefore,how to balance the relationship between accuracy and efficiency is the key to sheet metal stamping simulation.Based on the relevant theories of dynamic nonlinear finite element analysis,this paper conducts indepth research on the key technologies and applications of mesh adaptation in sheet metal forming simulation.The main contributions include the following:(1)In order to improve the accuracy of adaptive finite element analysis,a hybrid error estimation criterion based on element strain energy and stamping geometric characteristics is proposed,and an efficient adaptive mesh refinement strategy is established.First,a mixed error estimation criterion is established based on the proposed energy error estimation criterion and geometric error estimation criterion.Secondly,use the mixed error estimation criterion to judge,identify and mark the large deformation area where the local error exceeds the predetermined limit in the finite element discrete model.Finally,an adaptive grid encryption strategy is used to encrypt the regional grid,and a multi-point constraint method is used to deal with the noncoordinated grid.(2)In order to improve the efficiency of adaptive finite element analysis,a damper subcycling algorithm is proposed according to the characteristics of the difference in time step caused by the sparse mesh before and after the adaptation.The algorithm fully considers the influence of the metal sheet movement speed and acceleration during the stamping process: First,the adaptively encrypted sheet metal unit is divided into several regions according to the time step.Secondly,the damping factor is introduced based on the constant velocity sub-loop algorithm,and the different regions are numerically integrated according to the time step.Finally,compared with the minimum time step for all units after adaptive encryption,the damper subcycling algorithm significantly reduces the amount of integral calculation and improves the efficiency of adaptive analysis.The analysis of the calculation example shows that the higher the complexity of the part forming feature,the more obvious the efficiency of the algorithm is improved.(3)The contact friction algorithm and contact update algorithm for sheet metal forming based on the adaptive analysis mode are proposed,and the process of transferring and updating the physical variables of the old and new elements after adaptive meshing is established.The results of the numerical example show that the algorithm reduces the calculation cost of the adaptive finite element analysis of sheet metal forming and effectively improves the accuracy and efficiency of the solution.