Research On Damage Mechanism And Hybrid Design Of Composites For Automotive Lightweight

Carbon fiber reinforced composites have great development prospects in automotive lightweight owing to their excellent mechanical properties.However,the defects of carbon fiber materials and the cost restriction pose a great challenge to the automobile application.Therefore,the hybrid composites attract much attention which are widely investigated in recent research to overcome the limitation of single fiber composites.As a new material system,hybrid composites have stronger designability and are more flexible to be applied in the complex design scenarios.Motivated by the superior advantages of hybrid composites,this paper proposed the novel approaches with the optimization of the carbon fiber materials dropping into hybrid composite materials while the related applications in automobile panels are systematically investigated to verify the effectiveness of hybrid composite materials.Firstly,by adopting the design methods of single fiber mechanical properties,the optimal hybrid ratio range and stacking sequence were investigated to strengthen the flexural and low velocity impact properties of carbon-basalt fiber hybrid composites;Subsequently,the composite elastic constitutive model and damage degradation model were established to analyze the force and damage degradation regularities of hybrid composites.This process makes it possible to observe and study the damage mechanism of hybrid composites that cannot be obviously observed in the experiments;Eventually,the comprehensive performance of hybrid composite materials applying on the vehicle engine hood was optimized and verified so as to explore the prospect of hybrid composite applications in automobiles.The research of this paper is funded by The National Key Research and Development Program of China entitled "New architecture electric vehicle structure-material-performance integration multi-objective optimization design".The Main researches of this paper are organized as follows:(1)The optimal hybrid ratio range and stacking sequences of carbon-basalt hybrid composite materials were determined.Different kinds of hybrid composite laminates were assembled,and the flexural performance of materials with different hybrid ratios was analyzed through bending tests,while the variation characteristics of flexural strength were obtained.Then,the microscopic morphology was detected by scanning electron microscope(SEM)to compare and analyze the failure modes and mechanisms of composite materials.Hence,the relationship between hybrid ratios and microscopic morphology were achieved through the comparison.Additionaly,through low velocity impact tests on hybrid composite laminates with different hybrid ratios,the impact response and energy absorption capacity under different impact energies were systematically investigated and the influence regularities of different hybrid designs on the impact performance of composite materials were obtained.Ultrasonic C-scan was used to detect the failure area of the composites under low velocity impact load,so as to further study the effect of hybrid ratio on the low velocity impact performance and failure behavior of composites.Hence,the optimal hybrid ratio range and stacking sequence are determined through the investigation of flexural and low velocity impact performance.(2)The theoretical damage degradation model of composite materials was established and verified while the performance prediction and damage mechanism of hybrid composites were explored.By combining the strain-based Chang-Chang fiber strength theory,the fracture toughness stiffness degradation theory,and the cohesion element layering theory,a composite damage theory model was established for theoretical analysis.The effectiveness of this composite damage theory model was firstly verified by the comparison of the finite element method(FEM)and experiment results.Then,this theoretical model was applied to calculate and simulate the intralayer stress of composite materials with different hybrid design laminates.The relationship between the characteristic of the intralayer stress and the overall performance of the laminate helps to infer the effect of hybrid laminate on overall performance.Furthermore,the damage and evolution forms of hybrid composites were studied,and the damage forms of the matrix,fiber and interlayer interface under different external forces were analyzed.(3)The automobile engine hood of hybrid composite material was optimized and verified.The carbon fiber engine hood model was optimized with the experimental verification of its accuracy when the stiffness response values of the original steel engine hood under different working conditions were applied as the boundary conditions.To fully demonstrate the effect of hybrid structures,the performance of different hybrid structures under different working conditions was analyzed and compared.By simulating the pedestrian collision process,the pedestrian protection ability of the engine hoods produced by carbon fiber and hybrid fibers was evaluated through head injury criteria(HIC),maximum intrusion amounts,and energy absorption capacity.