Structural Optimization And Application Of Carbon Fiber/Polypropylene Sandwich Panels Based On Crashworthiness

With the continuous development of automotive lightweight research,the use of lightweight and high-performance composite materials to manufacture body parts and structural optimization technology has become two important research directions for achieving lightweight vehicles.At the same time,the maturity of composite material production and forming technology provides unlimited possibilities for the application of lightweight composite materials on the body.However,while reducing the weight of the car,how to ensure the safety of the car and the protection of the occupants in the accident is also an important issue in the research of lightweight materials and their applications.As a lightweight material,the foam sandwich panel composite structure has excellent properties such as high rigidity,light weight and good impact resistance.Under the collision condition,the sandwich panel can ensure the rigidity strength requirement of the component,and the core foam structure can generate crush deformation under the force condition,thereby effectively absorbing the impact energy.At the same time,its manufacturing process is relatively simple and the manufacturing cost is low,which increases the possibility of its wide range of applications.Compared with traditional metal materials,carbon fiber composite materials have many advantages such as high specific strength,high specific modulus,good heat resistance and good stability,so the application rate in the automotive field is increasing rapidly.As a commonly used lowdensity foam,foamed polypropylene has good cushioning energy absorption characteristics and good dimensional stability,and is applied to automotive energy absorption and vibration damping components due to its simple manufacturing process,low cost and recyclability.In this paper,a four-layer carbon fiber composite board is used as the upper and lower panels,and foamed polypropylene is used as the sandwich structure to prepare carbon fiber/polypropylene foam sandwich panels,and the related mechanical properties are tested and simulated.Multi-objective optimization method is applied to the interlayer.The plate structure and core foam density were optimized to obtain the optimal geometric thickness and foam density scheme.The application of the roof structure of a car and the topology optimization design were carried out,and the energy absorption effect was discussed based on simulation analysis.The specific research contents and research results are as follows:(1)The sandwich plate sample preparation was completed and the mechanical properties were studied.The preparation of carbon fiber composite board and the foaming method of polypropylene were introduced in detail.The bonding of carbon fiber and polypropylene foam was completed by means of bonding,and the preparation of the sample was completed according to the requirements of quasi-static test and impact test.Quasi-static compression test and three-point bending test on carbon fiber/polypropylene foam sandwich panels,obtain load-displacement curves and analyze related mechanical properties such as compressive strength,compressive modulus,flexural strength and bending stiffness;A low-speed impact test was conducted to analyze the impact resistance of the sandwich panel.Finally,the finite element simulation of the compression process and the impact process is carried out in the finite element software,and the simulation results are compared with the experimental results to verify the effectiveness of the simulation.(2)Complete multi-objective optimization of the sandwich panel structure.The top and bottom of panel thicknesses,foam core thickness and density are designed as four optimization variables.The energy absorption,deflection,peak force,thickness and mass are designed as five optimization targets.The energy absorption and deflection of the 1.2mm thick B400/780 DP high-strength steel plate and the total thickness of the sandwich plate are designed as three constraints to establish a sandwich panel impact model for multi-objective optimization design,to obtain an optimal foam sandwich panel structure and apply it to body parts.The final optimization results were as follows: the thickness of the top panel was 0.89 mm,the thickness of the bottom panel was 0.62 mm,the thickness of the foamed polypropylene core was 7.52 mm,and the density was 62.17 kg/m3.(3)Sandwich board application research.The multi-objective optimized sandwich panel structure is applied to a car top cover,and the top cover crashworthiness when the vehicle is turned over is mainly considered.According to the requirements of the regulations,the static crushing model of the carbon fiber/polypropylene foam sandwich panel is established.The core layer structure is optimized,and the foam core layer of the roof structure is optimized by optimizing the strain energy,that is,the maximum stiffness.The design can effectively reduce the amount of foam used under the premise of ensuring the rigidity and energy absorption requirements of the top cover.Finally,the optimized sandwich panel top cover is applied to the whole vehicle,and the roof crushing simulation is carried out.The results show that the optimized absorption energy of the sandwich panel is improved and the quality is reduced by 8.06%.