Research On The Constitutive Model Of DP780 Sheet Steel Under Strain Path Change And Its Spring-back Prediction

During the forming process of sheet metal,the sheet will be subjected to a complicated loading history.Changes in strain rate and strain path may be concentrated in the sheet forming process.The deformation and hardening behavior are usually characterized based on simple monotonic loading mechanical experiments,but the stress-strain curves obtained from mechanical experiments under complex loading conditions usually show various anisotropic characteristics.The characteristics of anisotropy are affected by the pre-stress variable and the degree of path change.The change of the strain path may cause the cross effect of the metal sheet,hardening stagnation,permanent softening or Bauschinger effect.Through the tensile test of the dual-phase(DP780)sheet steel under the variable strain path,the flow stress-strain curve obtained shows anisotropy.In order to predict the flow stress of DP780 steel plate under different pre-strain,strain and strain paths,a deep neural network hardening model is established;the data set is divided into training set,validation set and test set to train,verify and test the deep neural network Hardening model: The correlation coefficient between the prediction results of the test set and the experimental results is 98.88%.The surface deep neural network hardening model has strong predictive ability.At the same time,in response to the above phenomenon,a new phenomenological hardening model is proposed to describe the flow stress-strain behavior of sheet metal under variable strain path;this new model combines inverse hyperbolic cosine function,power function and inverse proportional function;the new model is accurate Describes the plastic deformation behavior of the dual-phase(DP780)steel plate after the strain path is changed at room temperature,and shows that it can mathematically formulate the plastic deformation behavior predicted by the deep neural network model.Combine the newly established hardening model of DP780 steel plate flow stress-strain behavior with the Von Mises yield criterion and the associated flow criterion to construct a constitutive model of the plastic deformation behavior of DP780 steel plate.The new constitutive model is finite elementized and user subprogrammed and imported into ABAQUS.Predict the spring-back of DP780 steel plate after stamping and unloading by simulating the Ushaped stamping/spring-back of DP780 steel plate.Compared with the experimental rebound results,the spring-back results predicted by the simulation have a smaller error,indicating that the new constitutive model can better predict the U-shaped stamping/spring-back of DP780 steel plate,and the constitutive model has good reliability.