| MIG welding is widely used in the connection of aluminum alloy body of new energy vehicles,and the welded joint is often the weak link of the body welded parts.Welding heat input leads to a complex structure of the weld and mechanical properties that are very different from the base material.Considering the mechanical properties of the weld is the key to the accurate CAE simulation of the body and parts.This paper takes Al6061-T6 and MIG welded joints as the research object,using experimental techniques and finite element simulation research methods,closely surrounding the fracture theory and failure model of metal materials,the mechanical properties of aluminum alloy base materials,the construction of aluminum alloy mechanical constitutive models,A lot of research work has been carried out on the mechanical properties of aluminum alloy MIG welds,inverse calculation and numerical simulation of aluminum alloy MIG welds.On the basis of introducing the fracture characteristics of metal materials,the characteristics and causes of brittle fracture of welded structures are analyzed.Analyzed the interpretation of the classic failure criterion to the fracture problem,and analyzed their advantages and disadvantages.The theoretical content,application methods and limitations of constant strain failure criterion are expounded.The three mechanical constitutive and failure models of GISSMO,GTN and JohnsonCook are introduced in detail.Their constitutive equations,failure formulas and ways of characterizing the failure process are analyzed.In addition,the application of three failure models in finite element simulation software is introduced.Uniaxial tensile tests under different sampling directions of aluminum alloy base materials were carried out to study the strain hardening,anisotropy and strain rate effects of aluminum alloys.Based on the improved J-C model,the constitutive equations of the aluminum alloy base material were fitted,and the accuracy compared with the original J-C model was compared.The mechanical constitutive model of the aluminum alloy base material constructed in this paper considers the effect of anisotropy on the rate-of-change effect,which can provide an accurate model basis for the next study of the collision deformation behavior of the aluminum body tailor-welded structure under large deformation and high rate.Using CMT welding technology,on the basis of self-made tooling and improved process,a tailor-made welding test of Al6061-T6 thin plate was carried out.Through the micro-hardness test,the hardness distribution characteristics of aluminum alloy CMT welds are revealed.An "equivalent dichotomy" is proposed to divide aluminum alloy CMT welded joints equivalently.Through the unidirectional tensile test of the welded joint,the tensile properties of the welded joint are obtained,and the mechanical properties of the welded joint are characterized by the connection efficiency.Through the tensile test of special samples of welded joints,the mechanical properties of welds under different stress states are revealed.Based on the LS-DYNA and LS-OPT software,finite element simulation and iterative optimization ideas were used to solve the weld parameters.A tetrahedral shell element was used to establish a numerical model of weld fracture failure.The radial basis function method is used to construct the proxy model,and the mean square error is used as the optimization goal.The material parameters of the weld are iteratively reversed.The parameters of the weld obtained by the reverse calculation are input into the finite element model of weld failure,and it is found that the simulation results are in good agreement with the test curves.The method of equivalent partition and iterative optimization adopted in this paper can be used in the reverse calculation of weld parameters and the construction of simulation model of fracture failure of welded joints,so as to improve the accuracy of collision simulation of tailor welded structure of aluminum alloy body. |
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