| Since 1950's, resistance Spot weld has become the primary method of joining in vehicle industry, due to the advantages it has in welding thin sheet parts, such as, concentration of energy, small deformation, high productivity. In the process of car body manufacture, the quality of spot welding will not only directly determines the manufacturing variations in car body welding assemble, but also determines the reliability and security of cars. As the increasing use of CAE analysis in car crash simulation, it has a great significance to improve the accuracy of FE model particularly in simulation reliably of the spot weld connections.Spot weld failure will greatly influence the vehicle response in crash. Spot weld failure is one of the most common research topic in vehicle design process. Using the experiments and finite element method, the current paper analysized the spot welds failure machenical in square-cup tension test and lap-shear tension test of high strength steel (DP600), which was wildly used in the automotive industry. FE models were built with solid elements to simulate the corresponding tension tests and validated by comparing the load-displacement curves. To validate the model in detail we performed experiments aimed to study the microstructure and micro-Vickers hardness distribution of the spot weld region. The detail FE models of spot weld consist of base sheets, Heat Affected Zone (HAZ) and weld nugget. In the FE simulation study, material failure is modeled with strain-based criterion. The research summarized the failure processes of two spotweld failure tests. The analysis of stress and strain in FE models show that notch between weld nugget and HAZ is the stress concentration points, which confirm the phenomenon that pull-out failure of spot weld often takes place at the heat affected zone around the weld nugget.Nowadays, there are many solutions of spot weld modeling in simulation of car crash. In order to research the imfluence of spot weld models in longitudinal beam crash, Firstly, the author classified and compared ten exsited spotweld models in difficulty and characteristics of modeling;Then, selected five typle of spotweld models, used commonly in present, to simulated the crash of certain longitudinal beam jointed by spotweld. Finally, with the compariment of real world test, it indicates that the model of spotweld will influence the deformation simulation of longitudinal beam, and the solid element model, deformable beam model and spring model have high precision of simulation. While spot weld model and rigid bar model are easy to define. But taking into consideration the new definetion method, deformable beam model will be the most convenient modeling typle in simulation of car. So the author regards the deformable beam model as the proper way in simulation of car crash.Finally, in order to study the influence of strength and distance of spotweld in longitudinal beam, the current paper built up three crash models of longitudinal beam with different strength of spotwelds and four crash models of longitudinal beams with different distance of spotwelds. According to the analysis, it can deduce a conclusion that strength and distance of spotwelds will influence the deformation and energy absorption of the longitudinal beam greatly. In detail, the capability of energy absorbing of longitudinal beam will decrease with the decline of spotweld stenght; and too large or too small distance would be detrimental to the deformation and energy absorption of longitudinal beam. |
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