Study On Compression Characteristics Of Crash Can Under Multi-damage Combination

As an important component of the bumper system,the automobile crash can is able to effectively absorb the collision energy and reduce the damage to the vehicle and its occupants in the event of vehicle collision.Most of crash cans for automobiles are metal thin-walled structures,which will cause damage inside the structure when impacted by a certain speed.The accumulation of damage to the limit value will cause material failure and change the deformation mode of crash box.The transform of deformation mode will directly affect the energy absorption level of crash can.In this thesis,according to the damage types and deformation modes of crash can during compression,a metal constitutive model with multiple damage forms is established,and the failure modes and deformation modes of crash can during compression are reasonably predicted,The specific research contents include the following aspects:1.The failure mechanism and deformation mode of metal thin-walled energyabsorbing structures are summarized.Based on the theory of continuous damage mechanics,a variety of constitutive models causing ductile fracture of metals are summarized,including elastoplastic constitutive model,damage criterion,damage evolution and element failure deletion,and the mechanism of metal from damage initiation to failure fracture process is explained.Combined with the existing crash can structures,the deformation modes of different types of crash cans under axial compression are classified,and the main deformation modes of four types of crash cans are sorted out,as well as the advantages and disadvantages of energy absorption effects of crash cans under each deformation mode.2.The energy absorption characteristics of steel crash can and aluminum alloy crash can are compared.Q345 steel crash can and 7108-T6 aluminum alloy crash can are selected.The steel crash can uses the John-Cook damage model,and the aluminum alloy crash can uses the combination of ductile damage,shear damage and collapse instability damage models.The energy absorption characteristics and final collapse shape of two crash cans are compared under the axial impact speed of 10m/s.Seven crashworthiness evaluation indexes of crash can were established to analyze the energy absorption effect of crash can.Through comparison,it is found that 7108-T6 aluminum alloy is more suitable as the energy absorption material of crash can under the medium-low speed impact.3.Analyze the influence of wall thickness and different damage criteria on the energy absorption characteristics of crash can.The change of crashworthiness of crash can is analyzed by changing the wall thickness of crash can and the combination of different damage models.The change of crashworthiness is mainly reflected in the distribution of stress and damage of crash can,transform of deformation mode of crash can,the fluctuation of the load-displacement curve in the collision process,and the increase and decrease of each evaluation index of crash.4.Research on compression characteristics of crash can under oblique loading.The included angle between the impactor and the axis of crash can is controlled to vary between 0° and 15°.There are four working conditions at 5° intervals.Compare the differences of the axial compression characteristics and crashworthiness rating indexes of the crash can under four working conditions.The results show that when the collision angle is greater than 5°,the crash can forms shear and tear deformation with shear band,and the crash can has overall bending deformation when the collision angle is greater than15°,and the overall collapse of the structure no longer absorbs energy.In this thesis,the analysis of the compression performance and deformation mode of the crash can under the condition of considering damage has improved the crushing behavior,energy absorption characteristics and deformation mode of the crash can under dynamic impact.The research results have important reference value for the durability of vehicle structures,the design of crash can structures and the improvement of vehicle crashworthiness.