Research On The Collision Protection Of Electric Vehicle Battery Box Based On The New Lattice Sandwich Structure

With the popularity of electric vehicles,battery safety has attracted more and more attention.Statistics show that the electric vehicle battery fire caused by collision accidents accounts for a high proportion,and the impact of foreign bodies on the ground is a more severe collision condition,which has a significant threat to the battery safety.In view of the advantages of high specific stiffness and specific strength of the composite lattice structure,a new type of lattice structure of carbon fiber composite is proposed and its mechanical properties are studied.It is applied to the battery box protection device to enhance the protection ability of the battery box against the impact of foreign bodies on the ground.Firstly,by changing the arrangement of traditional pyramid lattice structure,a staggered arranged pyramid lattice structure is proposed,which takes into account the advantages of simple fabrication process of traditional vertical lattice structure and small node spacing of oblique lattice structure.The relative density of the new lattice structure was calculated and the staggered lattice structure of the composite was fabricated by the snap-fit method.Secondly,theoretical,experimental and simulation methods are used to study the flatwise compression performance of composite staggered arranged lattice structure.Based on the mechanical analysis of lattice cell,the theoretical prediction formula of elastic modulus and compressive strength of staggered lattice structure is derived.The elastic modulus,strength and failure mode of the lattice structure are analyzed through the flat compression test,and the accuracy of the finite element model of the lattice structure based on the failure criterion and progressive damage law of composite materials is verified.The simulation results clearly show the failure reason of lattice structure under flat compression load,and it is found that the core damage is different in different layers.Through the simulation method,the influence of the length of the core truss and the ply angle on the flatwise compression performance is further analyzed.It is found that the elastic modulus,strength and specific strength of lattice structure decrease with the increase of truss length.The relationship between specific stiffness and truss length is not monotonic.The elastic modulus and strength of lattice structure are the highest when the lattice core is 0°/90° ply.Then,the bending performance of the lattice structure is studied by experiment and simulation.According to the three-point bending test data,the bending stiffness and specific bending stiffness of lattice structure are obtained.Under the bending load,the core of lattice structure breaks and the core debonds at the node.The three-point bending finite element model of lattice structure is established,and the accuracy of the finite element model is verified by comparing with the experimental results.The simulation results show that fiber compression damage and matrix tensile damage are the causes of core truss failure.It is found that the bending stiffness and specific bending stiffness of lattice structure increase with the increase of truss length.When the core is 0°/ 90°ply,the bending stiffness of lattice structure is the largest.Finally,the staggered arranged lattice structure is applied to the battery box protection device.The impact scene of foreign bodies on the ground is studied,and two typical impact conditions are determined.The battery box with carbon fiber lattice protection structure is designed,and the corresponding finite element simulation model is established.The simulation is carried out under two kinds of ground foreign body impact conditions.Compared with the battery box without protection structure,it is found that the lattice structure protection device can reduce the invasion of foreign bodies into the battery box and reduce the size of high stress distribution area of the box under two working conditions,and effectively improve the collision safety of foreign bodies on the ground of the battery box.