| The negative Poisson’s ratio(NPR)structure has the characteristics of lightweight,high specific energy absorption,and impact resistance.At the same time,it also has the "tensile expansion effect",which can enhance the stiffness and strength of the structure in the process of deformation.In addition,the direct relationship between the cell parameters,mechanical properties and energy absorption characteristics of the periodic NPR structure also shows the potential of its functional design,so it is widely used in the fields of automobile,aerospace and so on.The research on the crashworthiness of NPR structure can accelerate its application in the field of vehicle safety.At present,the research on the collision performance of NPR structures is mostly based on the ideal axial impact condition,and the influence of impact angle on crashworthiness is rarely considered.However,in the actual vehicle collision process,under different impact speeds,there is a certain angle between the axial direction of automobile energy absorbing parts and the collision direction.Therefore,it is necessary to further study the energy absorption characteristics of NPR structure under multi-angle and multi-velocity impact conditions.Based on the numerical simulation method,combined with the functional gradient design and multi-objective optimization design method,this paper has carried out a series of studies on the energy absorption characteristics of the NPR re-entrant honeycomb(RH)structure with different dimensions under multi-working conditions.Based on the bionic design principle,a RH structure with hybrid gradient is proposed,and the energy absorption characteristics under multi-working conditions are studied.The gradient RH structure with NPR is filled in the automobile crash box for multi-objective optimization design.The specific research contents are as follows:(1)Taking the two-dimensional RH structure as the research object,under the working conditions of different impact angles and different impact velocities,the better direction of comprehensive crashworthiness in two typical in-plane impact directions is selected,and the influence law of cell structure parameters on its comprehensive crashworthiness is studied.The dynamic response law,energy absorption characteristics,and deformation mode of two-dimensional RH structure under multiple impact conditions are summarized.An aluminum alloy sample is made and the axial compression test is carried out.Through the comparison and analysis of the simulation results,the reliability of the simulation model is verified.(2)Based on the two-dimensional configuration,taking the three-dimensional RH lattice structure as the research object,the direction with better comprehensive crashworthiness in two typical in-plane impact directions is selected to study the influence of cell structure parameters on the comprehensive crashworthiness of the structure under the multiple impact conditions.The dynamic response and energy absorption characteristics of the three-dimensional lattice structure under multi-working conditions are explored,and the deformation modes are summarized.The reliability of the finite element model is verified by making samples for the compression test and comparing them with the simulation results.(3)Combined with the functional gradient design principle and bionic design concept,a RH structure with hybrid gradient is proposed.Taking the two-dimensional and three-dimensional RH structure as the research object,nine different arrangements are designed,and the comprehensive crashworthiness and deformation modes of the structure under multi-working conditions impact is studied.Whether two-dimensional or three-dimensional,the results show that the comprehensive crashworthiness of the RH structure with the transverse negative gradient and the longitudinal positive gradient is better than that of other RH structures with hybrid gradient.(4)The three-dimensional RH lattice structure is used as the inner core to fill the automobile crash box.The comprehensive crashworthiness of the crash box filled with lattice structure is compared with that of other types of crash boxes under multi-working conditions.Through the multi-objective optimization design,the gradient-filled crash box with the best comprehensive crashworthiness is obtained.The results show that after optimization the comprehensive energy absorption of the crash box filled with lattice structure is increased by 12.3%,and the effect is remarkable.Meanwhile,the robustness analysis also shows that the optimal design scheme has good robustness. |
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