Effect Of Welding Residual Stress On Collision Safety Of Aluminum Alloy Anti-collision Beams

With the development trend of new energy vehicles,aluminum alloy is widely used as a lightweight material with high strength and corrosion resistance in vehicle safety structures.Compared to ordinary steel,aluminum alloy has poor welding performance,which can cause large welding deformation at the weld,forming large welding residual stress,and is prone to cracking and damage in the event of collision,affecting the overall safety.Currently,the research on collision safety of anti-collision beams mainly focuses on analyzing the anti-collision beams as a zero stress state,and there are certain errors between the simulation results and the actual results.Therefore,studying the impact of welding residual stress on collision safety can effectively improve this difference.In order to verify the accuracy of the welding model,through numerical simulation of the welding process of the T-joint and the lap joint at the junction of the anti-collision beam,it was found that the weld pool shape was in good agreement with the experimental data,the stress field simulation results were in good agreement with the experimental data,and there were large residual tensile stresses in the weld and adjacent areas.Based on the overall welding model of a vehicle anti-collision beam,this thseis analyzes the distribution of residual stress at the weld seam.The welding residual stresses at the ends of adjacent welding segments have a significant impact on each other,and there are large residual tensile stresses in the weld seam and heat affected zone;In order to reduce the residual tensile stress at the weld,an optimization study was carried out on the welding sequence and welding starting point of each welding segment.The changes in the longitudinal and transverse residual stress of each welding segment under different welding schemes were compared,and the scheme that can effectively reduce the welding residual stress was selected.The results show that there is a phenomenon of secondary heating at the end of the welding segment connected from end to end.The longer the secondary heating time or the shorter the time interval,the more residual stress is released at the end of the welding segment;The distribution trend of longitudinal residual stress in each welding scheme is similar,but the local stress concentration positions at the welding segment are different.The longitudinal residual stress along the weld direction has a significant impact,while the longitudinal residual stress values in the reverse welding sequence are generally small;The distribution trend of transverse residual stress varies greatly among different welding schemes,and the location of tensile stress concentration at the ends of each welding segment varies.In order to minimize the large longitudinal residual stress,the optimal welding sequence is the reverse welding sequence.Based on Johnson-Cook damage theory,the welding residual stress is used as the initial state to simulate and analyze the impact of collision avoidance beam collision,exploring its impact under the conditions of 2 mm/s three-point static pressure,42 km/h frontal 100% overlap high-speed collision,and frontal 40% offset collision.During the pressing process of the indenter,it was found that the welding residual stress caused a large stress level at the weld seam of the crossbeam,and the release of the welding residual stress caused a complex stress change in the weld area.The support reaction force fluctuated greatly during the high pressure leveling process of the bow,but the peak value changed slightly;In a 100% frontal collision,the stress values at each observation point of the energy absorbing box are generally too high,the collision force and acceleration peak values are reduced,the cracking time is advanced by 4.5%,and the damage location is different;In a 40% offset collision,the stress value at the observation point taken is relatively large,with a decrease in the peak value of collision force and acceleration.The cracking time of the energy absorbing box is 8.7% earlier,and there is a significant difference in the location of the damage.This indicates that the release of welding residual stress during the collision process will make the stress change of the energy absorbing box more complex,and the places with higher stress values will crack and damage in advance,resulting in a decrease in the bearing capacity of the anti-collision beam.