Lightweight Research On Electric Vehicle Hood With Carbon Fiber Reinforced Plastic

At present,China’s regulations on energy conservation,emission reduction and fuel consumption standards are becoming stricter.At the same time,this has brought new opportunities for the development of electric vehicles.In view of the problem of insufficient driving range for electric vehicles,reducing the mass of the whole vehicle is one of the most feasible ways.In view of the excellent performance of carbon fiber reinforced plastic(CFRP),such as lightweight,high strength,high modulus,high energy absorption capacity,combined with appropriate structural optimization technology,it is particularly suitable for automotive,especially for auto-body panels.This paper takes the automobile hood as the research object,and carries out lightweight design from the two aspects of material and structure.The main research contents are as follows:(1)An overview of the application status and theoretical research status of domestic and foreign carbon fiber composite materials on automobile panels and structural parts was made.The macromechanics theory of composite materials was introduced,including the constitutive relation and strength theory of single-layer materials,the stress-strain relationship and stiffness of laminated composites.This provided a solid theoretical foundation for the design,optimization and analysis of carbon fiber composite automotive hoods.The composite test specimens were fabricated by resin transfer molding(RTM),with 24 K carbon fiber and epoxy resin.The specimens were tested according to the ASTM series standards,and the mechanical properties of the materials,including modulus,strength,and Poisson’s ratio were obtained.This provided reliable material data input for the finite element simulation analysis of carbon fiber composites.(2)Eight conditions were determined to describe the various working conditions of the hood.A finite element model of the steel hood was established based on the vehicle modeling standard.The hood was analyzed according to the above working conditions,and its stiffness,strength and mode were obtained and evaluated.The results showed that all the evaluation indicators were within the required range,and they were used as design reference indicators in the optimization design.(3)According to the design principle of laminate and the principle of equal stiffness,the initial layup scheme of the inner and outer plates of carbon fiber composite hood was designed.The CFRP hood was optimized with two methods.The first was based on the initial scheme to optimize the layer thickness of single-layer materials.the second was segmentation optimization,which included the layer cutting shape optimization,thickness optimization,and layup sequence optimization.The finite element modeling of the composite hood was carried out.The performances of the steel hood,initial scheme and the optimized carbon fiber reinforced plastic hood were compared under the same working conditions.It was found that the initial CFRP hood and optimized carbon fiber composite assembly were qualified when the performance of the items was not lower than that of the original steel hood.And the optimized scheme has further weight reduction than the initial scheme.The overall performance of the second scheme is superior to the first scheme.The mass was significantly reduced.The second scheme reduced the weight by 51% compared to the steel hood and the effect of weight reduction was remarkable.The CFRP hood was made.The stiffness and modal tests were carried out.The comparison of simulation and test data showed that the results of the two were basically consistent,which effectively verified the feasibility of the optimization scheme and the simulation accuracy.(4)According to the C-NCAP(2018 version),the head collision area of the hood was divided by CATIA.According to the collision angle and speed given by the rule,the collision simulation of the adult and children’s head impactor with the steel hood and the carbon fiber composite hood was carried out,and the HIC value was obtained according to the acceleration-time curve of the center of gravity of the head during the collision.The safety performance of the hood depends on the size of the HIC.The results showed that the carbon fiber composite hood has better pedestrian head protection performance than the steel hood.The design of the carbon fiber composite hood was optimized in this paper,including the optimization of the layering shape,the thickness optimization,and the optimization of the layup order.Under the premise of ensuring the structural strength,rigidity and mode,the lightweight is realized.The application in automotive panels provides important guidance and reference.