Research On New Honeycomb Sandwich Engine Hood For Pedestrian Head Protection

The global automotive industry is growing rapidly,and car ownership continues to rise,bringing about road traffic accidents that increase year by year.Pedestrians are a vulnerable group in accidents,and the accident mortality rate is high.Therefore,it is urgent to design a flexible engine hood with good energy absorption and light weight for pedestrian protection.Negative Poisson’s ratio metal honeycomb materials have great potential in the field of engine hood pedestrian protection due to its light weight and high strength,as well as excellent energy absorption and cushioning performance.In this paper,the explicit dynamics finite element method is used to investigate the dynamic response characteristics of the chiral honeycomb sandwich engine hood with negative Poisson’s ratio effect during human-vehicle collision.Furthermore,the multi-objective optimization design of the hood was carried out around the performance requirements of pedestrian head protection.Firstly,this paper proposes a conceptual design of energy-absorbing sandwich engine hood with tetra-chiral honeycomb core.Finite element models of the headform impactor,the tetra-chiral honeycomb and the hexagonal honeycomb sandwich energy-absorbing engine hoods were established.The chiral honeycomb sample test and simulation results are consistent with the deformation mode and the stress-strain curve,which verifies the reliability of the finite element modeling method in this text.On this basis,the dynamic response characteristics of two sandwich engine hoods under human-vehicle collision were studied,and the results were compared and analyzed.The results showed that compared with the hexagonal honeycomb core sandwich engine hood,the pedestrian head damage value was reduced by 22.3% when using the tetra-chiral honeycomb core sandwich hood due to the negative Poisson’s ratio effect.Secondly,the influence of the key structural geometric parameters and collision position of the tetra-chiral honeycomb sandwich engine hood on its pedestrian head protection performance were analyzed and compared.Key structural geometry parameters include the cylinder radius of chiral honeycomb,the ratio of cylinder radius and ligament length,the cell wall thickness,the upper panel thickness,as well as the lower panel thickness.The results showed that the cylinder radius,the ligament length ratio and the cell wall thickness had a great influence on the pedestrian head protection performance.Finally,optimizations for the chiral honeycomb core sandwich engine hood were conducted by non-dominated sorting genetic algorithm.The key geometrical parameters were chosen as design variable,the minimum pedestrian head injury criterion value and minimum core thickness were chosen as optimization targets and the pedestrian head intrusion was chosen as constraint.Moreover,radial basis function method was used to create the response surfaces.The results showed that the multi-objective design significantly improves the head protection performance of the sandwich engine hood.The design ideas and adopted in this paper have certain guiding significance for the pedestrian protection engineering design in automobile and pedestrian collision accidents.