| Safety,environmental protection and energy saving have become three major topics of concern in the automotive industry.Lightweight body could reduce fuel consumption and reduce pollution.Improving the crashworthiness and energy absorption of the car can effectively reduce the danger caused by human operation errors.Therefore,the research on automobiles must take into account the light weight,the strength of the car body and the energy absorption characteristics of the car structure.Aluminum alloy has light weight,high specific strength and good ductility,so the thin-walled energy-absorbing structure processed by it is widely used in car bodies to achieve light weight,improve crash resistance and energy absorption.In this paper,key tests combined with finite element simulation are used to characterize partitioned cold metal transition(CMT)welded joints to obtain the corresponding damage parameters,to study the mechanical behavior of single-hat thin-walled structures with long welds and intermittent welds with different spacing under axial compression,and then to analyze the effect of weld damage on the deformation mode and energy absorption characteristics of single-hat thin-walled structures.Affected by the welding heat cycle,the chemical composition,structure and hardness of the welded joints are not uniform.The subdivision of welded joints is detailed in this paper to characterize its mechanical properties.The materials in each zone were subjected to smooth tensile,notched tensile and double-notched shear tests.It was found that the tensile strength of the weld zone increased by 23% compared to the based material zone and the brittleness tendency of the weld zone and the heat affected zone increased.The material damage parameters of the three zones were obtained.An axial compression test was performed on single-hat structures of different lengths,and it was found that the peak load is not affected by the length of the member.Affected by the non-uniformity of the mechanical properties of the weld,the average load value of the test is lower than the theoretical calculation value.By comparing and analyzing the results of the test,ignoring the damage and fracture simulation of the weld and considering the damage and fracture si mulation of the weld,it is found that the peak load,average load and energy absorption obtained by the latter simulation are slightly higher than the test results,which are quite different from the results obtained by the former simulation.It shows tha t the non-uniformity of the welded joint and the crack initiation and expansion at the weld have a great influence on the bearing capacity and energy absorption of the structure.The bearing capacity and energy absorption of single-hat structures with different weld spacing under quasi-static axial compression are predicted.It was found that when the weld spacing is a shrinked wavelength of 40 mm,the peak load of the component is the lowest,30.701 KN,and the average load is the highest,16.170 KN.The peak load is 7.78% lower than that of the continuous long weld connection member and the average load is 8.03% higher than that of the continuous long weld connection member.Compared with the single-hat structures with continuous long welds,the single-hat structures with intermittent welds absorb more energy and have a higher crush force efficiency(CFE)value.With the increase of the weld spacing,the energy absorption and CFE values showed a trend of increasing first and then decreasing,and reached the maximum value when the weld spacing was 40 mm,which was higher than the continuous long weld members 12.09% and 16.45% respectively.The components with intermittent welds all produce transverse fractures and longitudinal tears of the weld seams during the shrinkage deformation,but due to the existence of the weld spacing,which is weakly affected by the bonding force of the weld,the deformation of the component is easier.Thus,the overall performance is the improvement of the bearing capacity of the structure. |
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