Design And Optimization Of A Curved Honeycomb Sandwich Hood

Honeycomb sandwich structures possess many excellent characteristics such as lightweight,high stiffness,high modulus and good vibrate isolation,which has become an important structure for energy saving and emission reduction.However,most of the research are concentrated on flat honeycomb sandwich structures and few related on curved structures.In this paper,double curved honeycomb sandwich core was investigated by mechanical analysis and equivalent elastic parameters were obtained.Simultaneously,to investigate the performance of the sandwich structure hood,the equivalent mechanical model was applied to a sandwich structure hood with carbon fiber reinforced plastic(CFRP)plate and aramid paper(Nomex)honeycomb core.Contributions in this paper are listed as follow:(1)The structural characteristics of the hyperboloid honeycomb core were introduced.According to the Bernoulli-Euler beam model,the curved honeycomb sandwich core was discussed by mechanical analysis,the equivalent elastic parameters of the hyperboloid honeycomb sandwich core were deduced.Then the equivalent mechanical model of the curved honeycomb sandwich structures was established.(2)The sandwich structure with Nomex honeycomb core and CFRP skin was manufactured,and a three-point bending experiment was carried out.The corresponding finite element model was established.Detailed models of the honeycomb sandwich structure were established.Simultaneously,the corresponding equivalent models were built on the sandwich theory and curved sandwich theory,respectively.The two equivalent mechanical models were compared through finite element analysis which has been verified by the previous experiment.(3)A double-curved sandwich hood consisting of two CFRP skin and Nomex honeycomb core was designed based on the curved equivalent model and a traditional metal engine hood.The Finite Element Method(FEM)was used to analysis the hood performance.Under the premise of better rigidity performance,the sandwich hood has a great mass reduction compared to the metal hood.Afterwards,the sandwich hood was optimized with OPTSTRUCT software.The mass of the optimized structure was further reduced while maintaining the original rigidity.(4)In order to evaluate the pedestrian protection performance of the new structure hood,this study carried out the design and verification of the finite element model of the adult head impactor.The model was verified by the dynamic test standards which have been specified in the 2018 China New Car Assessment Program(C-NCAP).Then the impact simulation of the head-to-hood was conducted in LS-DYNA to verify the new structure’s ability of pedestrian protection.Finally,the better pedestrian protection capability of the new hood is shown by comparing the simulation results of the new composite sandwich hood and the traditional steel hood.The research results of this paper enrich the theoretical model of honeycomb sandwich structures to a certain extent,expand the application range of CFRP-Nomex paper honeycomb sandwich structures,and accumulate experience for studying the application of the structures in automobiles.The optimization design method adopted in this paper has a certain reference value for the structures with similar material and lightweight design of automobile body structures.