Dynamic Constitutive Relations Of Welding Spots Of Automobile Bodies

When a car crash is happening, a dynamic load is loading on the car. The body and the connecting parts absorb energy through deformation or failure. In this way the collision energy which transmitted to the vehicle crew is reduced. In a new car development, the collision process is simulated by experiment and simulation, this is an important part of the passive safety design. The experiment in the new car development is necessary; and CAE numerical simulation analysis has so many advantage like shorting the development cycle of new cars, reducing cost, changing design easily. This method is also being widely used in the new car development. To make the simulation more precisely, it must be required to ensure that the car model and condition can accurately express the actual situation. Resistance spot welding is one of the most important and the most one of connection method in the car body. When under a dynamic load, Spot weld with accurate mechanical properties in car model is very important for simulating.Current methods to simulate the spot welding is using simple element, by defining the contact and failure criteria to express the mechanical effect of the solder joints in a car model. In order to more accurately simulate the mechanical properties of solder joints, this article will research and analysis the constitutive as a single material. First, solder specimens based on DC53 DZ metal for constitutive researching is designed carefully, then the quasi-static tensile test is carried out by using MTS, and the dynamic tensile tests are carried out by using SHTB. Solder material is a metal material and the mechanical properties of the base material and joint have similar characteristics. In this paper, the Comper-Symonds constitutive model is used for solder material. Then the dynamic tensile testis simulated,the result show that the stress and strain is uniform within the specimen during the test. It can meet Hopkinson bar test assumptions, verify specimen design is reasonable. At the same time, with the constitutive parameters obtained from the experiment, the dynamic tensile test process reproduced with simulation is in good agreement with the real test and the dynamic tensile test result is verified.The static and dynamic tensile test on lap solder joint specimens are also carried out. The test results show that the solder joint strength is different when load condition is different. Under the dynamic tensile load, solder lap shear strength of the specimen is higher than static strength. Dynamic tensile testing with four different strain rates show that the shear strength of the solder joint is very close. The dynamic tensile test of lap joints specimen is simulated,and the spot weld constitutive relationship is substituted into the model.The results indicate that the FEA model of spot weld can express real stress situation of joint in the specimens and can accurately express real ligation. Then the model is compared with several other simple joints element model and the result shows that using solid elements with the weld material constitutive relation can express more precisely the spot weld force situation and ligation in the lap shear specimens.Finally, all our research results show: The spot weld C-S with constitutive relationship determined by result of experiment can accurately express dynamic mechanical properties of solder joints; When the solder joints under shear tensile load, static tensile shear strength characteristics can not be replaced by dynamic shear strength, and in four different sets of strain rate loading tests in this paper, the shear strength of the solder joints is close; Compared the solid elements which with the constitutive model with several simple element to simulating spot weld, the simulation result show that the former is more consistent with the actual.