Study On Kinematic Hardening Behavior And Calibration Strategy Of High Strength Steel Plate

The springback problem has always been a research hotspot in the sheet metal stamping process.Due to the strong path dependence of high-strength steel materials strengthening,the springback behavior after unloading is affected by the coupling of complex loading paths and nonlinear unloading paths,making the accurate prediction of high-strength steel sheets more prominent.Accurate acquisition of test data on material hardening behavior is the basis for studying the properties of plates.Different hardening models have different degrees of accuracy in describing mechanical behavior.How to develop a more intelligent and rapid identification method for constitutive parameters and accurately match test data with the model is the research focus.Therefore,this paper conducts the kinematic hardening mechanical behavior testing,analyzes the evolution process of the subsequent yield surface,and formulates corresponding identification strategies for different hardening model parameters.The optimization strategy of relevant parameters is of great significance for building intelligent production line,predicting forming quality and planning production process.The main research contents of this paper is as follows:In order to accurately obtain the mechanical behavior data of high-strength steel plate and avoid common defects,some experimental devices were developed:（1）A test device for uniaxial tensile compression testing has been designed with a spring clamping device and a comb shaped support structure to prevent buckling and instability of the specimen during compression;（2）The free end effect of shear deformation is analyzed to develop a shear fixture that is conducive to large deformation,which overcomes the disadvantage that the tension and compression fixture is not conducive to accurately obtaining the large deformation data of the plate due to the existence of lateral forces on both sides;（3）The bending experiment device with adjustable mold span was used,and the characteristics of the elastic-plastic section of the plate bending were enlarged by adjusting the size of the bending mold reasonably.At the same time,a suboptimal model for reverse identification of elastic modulus is established based on the bending analytical model.The bending and springback stress conditions were studied,and the control of the yield surface and the evolution process of back stress by the ordinary kinematic hardening model and model with boundary interfaces were elaborated.The Yoshida-Uemori（YU）kinematic hardening model with variable elastic modulus was established by incorporating nonlinear unloading modulus.The matching strategies of linear and nonlinear kinematic hardening models and YU hardening models with boundary interfaces are determined.Different optimization orders and objective functions are set according to the parameter types of each model,and a parameter optimization and identification platform is established.At the same time,the seven hardening parametersY、B、C、b、m、R_{s at}、hof YU model are decoupled according to the physical meaning of each parameter,and identified by correlation method and optimization method.The recognition results and convergence residuals of the four hardening models are compared.The convergence consistency of the parameter results is tested.The results show that the YU model has the highest matching accuracy,the multiple nonlinear kinematic hardening model has little improvement in accuracy compared with the single nonlinear kinematic hardening model,and the linear kinematic hardening model is only suitable for low-precision prediction.Subsequently,the finite element simulation of bending springback of high-strength steel plate was carried out by using the optimized identification results of each model parameter.After comparing the prediction differences of each model,the YU model has a higher prediction accuracy for rebound,and the prediction error results of other models are acceptable.