| Numerical simulation is necessary in the process of automobile design and development,and the characterization accuracy of material mechanical property data has a direct impact on the analysis results.Lightweight materials play a direct role in energy saving,emission reduction and safety assurance of automobiles.However,due to the complexity of service state of these materials in practice,the existing theories can not describe all kinds of deformation behaviors of materials well.In this paper,the large deformation process of typical lightweight materials from uniform hardening,necking to fracture has been systematically studied by combining physical experiments and finite element inverse optimization,and the material data representation technology considering various factors has been developed.The main work and conclusions are as follows:(1)The plastic hardening behavior of material in the stage of uniform deformation is characterized based on the advantages of simple form and easy handling of hardening model,Combined with the uniaxial tensile test of 22 Mn B5 high strength steel under different deformation rates,the inverse optimization method of finite element is used to identify and optimize the parameters of Swift,Voce and Hockeet/Sherby models automatically,and the optimal hardening model and its related parameters under different strain rates are obtained.Digital image correlation(DIC)method is used to detect and simulate the tensile test under other four conditions in contrast.It is proved that the method of using the finite element inverse optimization method to determine the model parameters has high accuracy and is convenient and feasible.(2)The strain behavior of non-strain rate sensitive materials after necking at various strain rates is characterized by the extending constitutive curves of quasi-static materials.Swift model,Hockeet/Sherby model and their mixed SHS model are used to simulate the deformation process after necking combined with uniaxial tensile test and finite element inverse method at different rates.It is found that the single hardening model is difficult to accurately predict the deformation behavior of 22 Mn B5 high strength steel after necking,while their mixed SHS model has the highest representation accuracy.A good result is obtained by using the extending curve of material to simulate the side impact of B-pillar.(3)The influence of strain rate effect should be considered when the strain rate sensitive material is extended.A rate independent “material mainline” can be obtained by normalizing and scaling the constitutive curve of strain rate sensitive materials through necking points.A rate dependent coupling model of constitutive curve extension is developed by using the inverse finite element method to extend the mainline.Based on the tensile tests of 6016 aluminum alloy at different speeds,the parameters of the coupling model are fitted and the material constitutive curve after extension is deduced for numerical simulation.The simulation results are in good agreement with the physical tests.(4)Combined with physical test and finite element parameter reverse method,the parameter curve of GISSMO fracture model is calibrated,and the multi factor of GISSMO failure model is obtained.Taking 22 Mn B5 high strength steel as an example,the effects of strain rate,grid size and stress state on the accuracy of fracture simulation are studied.The three-point static pressure test of B column is simulated by using the multi factor GISSMO fracture failure card established,and the failure behavior of component material is predicted accurately. |
PDF Full Text Request