Study On Energy Absorption Characteristics Of Thin-walled Structure With Surface Nano Crystallization Treatment

With the improvement of living standards and the acceleration of urbanization,people's demands for transportation are increasing,faster and safer transportation vehicles are in great need in large cities.Railway vehicle is a kind of transportation with high speed,large passenger capacity and high safety,which greatly meets the daily traffic demand of large cities.In the design of railway vehicle industries,energy absorption devices are important components to absorb collision energy through plastic deformation and ensure safety,which mainly composed by thin-walled metal structures.Traditional energy absorption devices are mostly made by single-layer metal thin-walled square structures,and mainly using techniques such as preindentation,adding additional structure or other ways to control the structural deformation modes under impact loading,so as to improve the energy absorption capacity.In this paper,the nano crystallization technology and structural design of metal thin-walled structures are introduced in the design of energy absorption devices for railway vehicles.On one hand,metal thin-walled structures are processed by employing local surface nano crystallization to achieve its deformation control under impact load,while on the other hand,the metal thin-walled structures are designed with double-layer nested manners,thus a new kind of local nano crystallized double-layer embedded energy absorption devices of rail vehicles are proposed.Compared with the traditional energy absorption devices for railway vehicles,the new proposed energy absorption devices in this paper display the positive characteristics such as easy processing(no need to prefabricate defects or punch holes),simple design(local nano crystallization stripes can be digitally processed),significant improvement in energy absorption effect(energy absorption increased by more than 20%).The main research contents are as follows:1.Research on the buckling behaviors of the local surface nano crystallization metal plates.The ABAQUS software was used to establish the models of nano crystallized rectangular thinwalled plates and critical buckling loads were calculated.The effects of different local nano crystallization layouts(perpendicular to the loading direction,parallel to the loading direction,checkerboard blocks)on the critical buckling loads were analyzed.Results showed that the critical buckling load of nano crystallized metal plates were significantly higher than that of original metal plate,and the design with local nano crystallization stripes paralleled to the loading direction exhibited highest critical load.2.Study on the energy absorption characteristics of local surface nano crystallized singlelayer metal thin-walled square tube.The parameterized model was established by ANSYS,LSDYNA module was used to simulate structural energy absorption under impact load,and the influence of local nano crystallization layouts(nano crystallization layouts with circumferential stripes and even distributed stripe numbers)on the energy absorption effect was analyzed.Results showed that the energy absorption of the single-layer metal thin-walled square tube were improved with circumferential nano crystallization stripes,and an optimal number of nano crystallization stripes was obtained,that is the optimal model which tended to saturation state for the energy absorption capacity.3.Study on the energy absorption characteristics of local surface nano crystallized doublelayer nested metal thin-walled square tubes.First of all,three kinds of double-layer nested metal thin-walled square tube structures(the lengths of inner and outer tube are same,the length of inner tube is larger than the outer tube,the length of inner tube is smaller than the outer tube,)were established by ANSYS.Through numerical analysis,it is found that the models with higher outer tube length and smaller inner tube length were reasonable double-layer nested designs.Secondly,the effect of local surface nano crystallization layouts and stripe numbers on the energy absorption characteristics of the double-layer nested energy absorption devices were studied.Results showed that the energy absorptions of the local nanocrystallized structures with two optimal local nano crystallization layouts were significantly improved,the corresponding buckling deformations were more stable,and optimized stripe numbers were obtained for the two local nanocrystallization layouts.Compared with the single-layer model,the deformation for the double-layer structure was more stable and the energy absorption was more superior.