Study On Negative Poisson’s Ratio Multi-hierarchical Structures And Their Application On New Energy Vehicle

New energy vehicles have now become the main direction of the development of the automotive industry.The huge amount of traditional fuel vehicles has caused huge pollution to the environment due to the exhaust emissions generated during the driving process,and the use of non-renewable energy also makes the problem of resource depletion increasingly serious.The good energy-saving and emission-reduction properties of new energy vehicles have been widely recognized all over the world.The development of new energy vehicles is of great significance to alleviating air pollution and climate change,and is valued by governments and automobile companies.Due to the addition of battery packs and other components,new energy vehicles are more urgent to lightweight.New energy vehicles face greater challenges in collision safety due to their vehicle layout characteristics and power system.Therefore,the research on the lightweight and crash performance of new energy vehicles is extremely important.However,the development of new energy vehicles still has major limitations in the research and development of lightweight and crash safety performance.Due to the limitations of related manufacturing processes,connection processes and optimization technologies,traditional structural lightweight methods often sacrifice certain crash performance.on the other hand,the improvement of collision performance will lead to the increase of car quality.Therefore,this paper conducts a systematic study of the problems in the design of lightweight and crash performance of new energy vehicles,and explores new methods that can improve the crash performance of new energy vehicles while also improving their lightweight level.Both the negative Poisson’s ratio structure and the biomimetic hierarchical structure have excellent mechanical properties,and have huge performance advantages in terms of elastic modulus,energy absorption,fracture resistance,and bearing capacity.Based on the special physical characteristics and excellent collision performance of the negative Poisson’s ratio structure and the bionic hierarchical structure,this paper proposes new types of negative Poisson’s ratio multi-hierarchical structures,which combines the characteristics of both the negative Poisson’s ratio structure and the bionic hierarchical structure.This paper focus on the mechanical mechanism research,crash performance research,sandwich structure design and new energy vehicle application of these novel structures.It is hoped that it can provide a new reference method for the lightweight design and collision safety design of the development of new energy vehicles.Based on this,the work carried out and completed in this article is mainly reflected in the following:1.A series of novel negative Poisson’s ratio multi-hierarchical structures are proposed,which realizes the combination the characteristics of bionic hierarchical structure and negative Poisson’s ratio structure.The relationship between the geometric parameters and the macroscopic parameters of the negative Poisson’s ratio multi-hierarchical structures is established,and the relative density expression is derived through the proportion of the matrix material in the structure cell.Based on Euler beam theory,the expression of relative stiffness in the in-plane direction is derived,and the energy absorption mechanism of negative Poisson’s ratio multi-hierarchical structures is introduced in detail.Through 3D printing technology,a series of negative Poisson’s ratio multi-hierarchical models are manufactured using resin materials,and the negative Poisson ratio of these structures are verified through compression experiment.2.The impact performance of negative Poisson’s ratio multi-hierarchical structures is studied,and the crushing performance of negative Poisson’s ratio multi-hierarchical structures and traditional negative Poisson’s ratio structure are compared.Their finite element models are established.The focus is on the mechanical properties of negative Poisson’s ratio multi-hierarchical structures in the X and Y directions under quasi-static conditions with the same relative density,their deformation mode,stress performance,energy absorption performance and mechanism and the performance of negative Poisson’s ratio have been systematically studied and compared with the traditional re-entrant structure in detail.The influence of the impact velocity on the stress performance and energy absorption capacity of the negative Poisson’s ratio multi-hierarchical structures is also discussed emphatically,and the deformation modes of the negative Poisson’s ratio multi-hierarchical structures under different speeds are compared.The relative density parameters of the structure are changed by changing the wall thickness of the negative Poisson’s ratio multi-hierarchical structures,and the influence of the relative density on the energy absorption capacity and stress are discussed.3.A variety of negative Poisson’s ratio multilayer sandwich structures are proposed,and the effects of core distribution and gradient distribution on the deformation mode,collision force and energy absorption of the sandwich structure are effectively analyzed.The negative Poisson’s ratio multi-level structure is introduced into the sandwich structure design,and a series of negative Poisson’s ratio multi-level sandwich structures are proposed,and these new types of sandwich structures are systematically analyzed.The equilateral triangle substructure and regular hexagon substructure are introduced into the design of the sandwich panel,and the influence of multiple structural parameters on the collision performance of the sandwich panel is considered.The influence of the gradient distribution on the mechanical properties is discussed.The equilateral triangle substructure and regular hexagon substructure are introduced into the design of the sandwich beam,and their bending performances are discussed.4.The application of negative Poisson’s ratio multi-hierarchical structures in new energy vehicles was explored,and a new type of negative Poisson’s ratio bumper system and a new type of negative Poisson’s ratio crash box were proposed.Based on the excellent energy absorption performance of the equilateral triangular hierarchical honeycomb structure in impact load and bending deformation,it is introduced into the design of new energy vehicle bumper system and crash box.By putting the negative Poisson’s ratio multi-hierarchical filling core into the hollow bumper system and crash box,the collision performance of the bumper system of the new energy vehicle is improved.The optimal Latin square sampling method is used to generate sample points within the range of design variables,and the corresponding finite element models are established,and the output response of the model are calculated through Ls-Dyna.The corresponding surrogate models are established,and the multi-objective optimization algorithms are used to find out the optimal solution of the bumper system and crash box.It is successful to realize the optimization of the relevant design parameters of the negative Poisson’s ratio bumper system and crash box,and further improved the collision performance of new energy vehicles.