Research On Impact Protection Structure Of Polyurea Coating For Battery Pack Of Electric Vehicles

The battery pack of electric vehicles is generally located at the bottom of the vehicle,and it is prone to short circuit,fire and other risks due to bottom collision.Steel plates and aluminum plates are widely used as the protective structure of battery pack in the industry,but it is difficult to balance battery collision safety and lightweight issues with metal plates.Polyurea is a kind of elastomer polymer with superior impact protection characteristics,which has been widely studied and applied in the field of military explosion-proof and bulletproof.In this paper,the protective effect of polyurea coating on aluminum / steel baseplate was studied.Firstly,the impact mechanical response of polyurea coated battery pack bottom plate was studied by means of finite element simulation and experiment.The impact condition of the battery pack bottom plate is simplified to the equivalent square plate perforation condition.The equivalent condition ensures the consistency with the original condition in terms of maximum equivalent strain and strain rate.The research further completed the quasi-static perforation test and the low-speed and high-speed perforation impact test of the equivalent square plate structure.The mechanical response of the square plate structure with aluminum / steel baseplate without polyurea coating and with polyurea coating on the front / back impact surface was investigated.The test results show that the polyurea coating structure can delay the breaking time of the baseplate and increase the peak force of the structure under the impact of high-speed perforation.Subsequently,this thesis carried out the mechanical testing and mechanical behavior characterization of polyurea materials and 6061-O aluminum alloy.In this study,the Ogden model and the generalized Maxwell model were used to describe the hyperelastic and viscoelastic mechanical behavior of polyurea materials,and the modified JohnsonCook model was used to describe the mechanical behavior of aluminum materials.By substituting these two material models into the equivalent perforation model,the model accurately simulates the mechanical response of the polyurea coating structure before the aluminum baseplate fractures,and can predict that the polyurea coating can delay the fracture time of the aluminum baseplate.This thesis analyzes the protection mechanism of polyurea coating through simulation model: when polyurea is coated on the back impact surface of the baseplate,it can provide support for the baseplate and increase the energy consumption of the baseplate;when polyurea is coated on the impact surface of the baseplate,it can reduce the stress concentration phenomenon at the collision part of the baseplate,and delay the fracture of the baseplate.Finally,the structure of polyurea coating was analyzed by parametric method,and the influence of polyurea strength,baseplate strength,interface bonding strength and polyurea coating thickness on the protection performance was explored.In the range of parameters discussed in this paper,the impact resistance of polyurea coating structure increases with the increase of polyurea strength.The protective effect of polyurea coating on low strength and high toughness baseplate is more obvious.The interface bonding strength mainly affects the mechanical response of the baseplate after fracture.Although the increase of polyurea coating thickness leads to the increase of mass,the effect of energy absorption is obviously greater than the cost of mass increase.