| Resistance spot welding (RSW) is widely used for joining sheet metals of car body inautomotive industry due to its advantage of light weight, high static strength, reliability,performance stability and ease of automation. As the main car body assembly process, RSWtake on more than75%of the car body assembly work. A car body contains about4000~6000spot welds,. The effect of strength, failure as well as distribution of spot weldson the car body performance should not be ignored. As the crash simulation plays anincreasingly important role in the design of automotive passive safety, it is important anddifficult for improving the crash simulation accuracy to simulate the spot welds and itsfailure correctly. Therefore, in this paper, the failure simulation of spot welds in the frontrails crushing was studied and the impact of spot welds arrangement on the deformation andenergy-absorption of front rails was investigated. The main results are as follows:(1) The spot welds failure in front rails were regarded as research object. The Results-basedspot failure criterion and the pertinent failure parameters were determined. First, the forceand load condition was analyzed. The results-based failure criterion in LS-DYNA simulationplatform was chosen. Then, the drawback of test method for determining failure parameterswas studied and KSII spot weld sample was adopted and relevant equipment was designed.Finally, the shear strength of KSII0°and Lap-shear test under different spot weldsdiameter was analyzed through spot weld coupon test. The results showed that for qualityspot weld, the shear strength from KSII0°was9.2%larger than that from Lap-shear. TheKSII0°test eliminates the bending moment effect and the spot weld rotation was relieved,indicating KSII0°measurement result more truly reflect the shear capacity of spot welds.(2) The spot weld failure model based on KSII test was established and the effectiveness ofthe model was validated through front rail crushing test. First, the8-HEX from LS-DYNAwas chosen as the spot weld element. The simplified KSII0°simulation prove the contactreliability of this spot weld element. Combining the simulation and test, the materialparameter of spot weld was calibration and the yield strength and tangent module wasdetermined. The simulation force-displacement curve after calibration is in good agreementwith the experiment result. Then, the KSII0°and Lap-shear test and simulationsuccessfully validate the established spot weld failure model. Finally, the simulation andexperiment results from front rail crushing were analyzed and the spot weld failure modelwas proven effective and accurate.(3) The effect of spot weld layout on the front rail deformation and energy-absorption wasstudied through front rail crushing simulation. According to typical wavy bucklingcharacteristic of thinned-walled beam crumple deformation pattern, two spot weld layoutschemes was determined, namely spot welds were located in the peaks and valley (refer to itas extreme position) of buckling waveform and spot welds were located in the equilibriumposition. The finite element model of thin-walled straight beam and front rails under twospot weld arrangement were established respectively. The simulation results were analyzedintegrating pertinent literature. For the crushing of thin-walled straight beams, spot on extreme position of buckling waveform showed superior deformation and energy-absorptionto spot on equilibrium position. In this dissertation, the research on spot weld layout of frontrails containing local structure feature such as induction slots and holes was carried out. It isfound that spot weld distribution had no significant effect on the front rail deformation andenergy-absorption. The crushing deformation was mainly effected by the local structurefeature and spot weld arrangement played less role on the front rails deformation andenergy-absorption. This conclusion can provide reference for the structural design and spotwelds layout of front rails... |
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