| Automotive safety research has become the most important part of automotive technology.The research on energy absorption of materials and structures during collision is an important part of passive safety of automobiles in collision.Thin-walled metal structures have been widely used in the energy absorbing structure of automotive buffer systems because of their light weight,low cost,and the ability to effectively dissipate a large amount of impact kinetic energy during impact.This thesis focuses on the innovative design of the energy absorption structure in buffer system,and comprehensively utilizes various research methods such as theoretical analysis,experimental technology,numerical simulation and multi-objective optimization,and proposes a variety of new energy absorption structures and carries out systematic crashworthiness research.The main research works of this paper are as follows:(1)Experimental and theoretical study on crashworthiness of star-shaped tubes under axial compressionThe research on the crashworthiness of existing thin-walled structures mainly focuses on the theoretical analysis and performance improvement by proposing different structures,while few studies on the effect of manufacturing processes on the crashworthiness of thin-walled structures.The paper systematically carried out the experimental analysis of several star-shaped tubes,i.e.,the hexagonal,octagonal and twelve corners,which were made with different material and fabrication methods under axial compression.The study found that the mean crushing force of the octagonal star-shaped tubes is increased by 7.94% compared to the hexagonal star-shaped tubes,while the mean crushing force of the twelve corners star-shaped tubes is reduced by 15.75% compared to the octagonal star-shaped tubes.The research on the crashworthiness of the star-shaped tubes by different processing methods shows that the processing method has a certain influence on the deformation mode of star-shaped tubes,but has a limited influence on the overall crashworthiness.Based on the simplified super folding element theory,a theoretical formula of the mean crushing force under the axial compression of the star-shaped tube is obtained.(2)Design and crashworthiness optimization of a lateral corrugated tube with a sinusoidal cross-sectionA new type of lateral corrugated tube with a sinusoidal cross-section is proposed.The topological evolution of the cross-section can be controlled by amplitude,basic nominal radius and number of corrugations.The crashworthiness study of the structure was carried out using experiment,numerical simulation and multi-objective optimization.The results show that the amplitude,the number of corrugations and the wall thickness are important parameters that affect the structural deformation mode and crashworthiness.When the number of corrugations is 6 and 8,the specific energy absorption are increased by 27.91% and 27.24% respectively compared with that of the ordinary circular tube.The parameterization study of amplitude,nominal radius and wall thickness on structural crashworthiness is carried out.The main effects and interaction effects of structural parameters on crashworthiness index are systematically analyzed.The results of multi-objective optimization show that the lateral corrugated tube has better crashworthiness,a wider range of application and design space than ordinary circular tube.(3)Study on crashworthiness of a novel sandwich sinusoidal lateral corrugated tubes structuresA novel sandwich sinusoidal lateral corrugated tubes was proposed.It consists of the outer circular tubes,the inner circular tubes and a new type of lateral corrugated tubes with a sinusoidal cross-section in the middle.The crashworthiness study of the structure was carried out using experiment,numerical simulation and multi-objective optimization.The results show that the deformation mode of the middle lateral corrugated tubes is significantly different from that of the individual compression due to the limitation of the outer and inner circular tubes,and it has obvious interaction effect.The energy absorption is increased by 35.6% compared to the individual compression of its constituent tubes due to the interaction effect.The proposed sandwich sinusoidal lateral corrugated tubes have a larger effective crushing displacement,a lower initial peak force and better compression stability than sandwich star-shaped tube.Parametric studies show that the wall thickness of inner circular tubes plays an important role in the specific energy absorption,while the wall thickness of outer circular tubes plays a major role in initial peak force.Multi-objective optimization studies were carried out on sandwich sinusoidal lateral corrugated tubes with 6 and 10 corrugations,respectively,and almost identical optimal solutions were obtained,but they were achieved by completely different structural parameters.(4)In-plane impact dynamics analysis of sinusoidal honeycomb structure with negative poisson's ratioA novel sinusoidal honeycomb structure with negative Poisson's ratio is proposed.The dynamic response of honeycomb structures with different amplitudes and thicknesses under different velocity impacts is analyzed,and the energy absorption research is carried out.The results show that the reaction force fluctuation under in-plane impact is closely related to amplitude,wall thickness and impact velocity.The reaction force of the sinusoidal honeycomb with thicker wall thickness and smaller amplitude has more significant fluctuations than the sinusoidal honeycomb with larger amplitude and thinner wall thickness.At the same time,the higher the impact speed,the more obvious the reaction force fluctuations.The platform stress at the fixed end is related to the thickness of the honeycomb,independent of the impact velocity.The energy absorption capacity of the honeycomb structure decreases with increasing amplitude,and the sinusoidal honeycomb structure with slight auxetic has better energy absorption capacity than the conventional hexagonal honeycomb structure.(5)Crushing analysis and multiobjective crashworthiness optimization of multi-cell conical tubeA novel multi-cell conical tube is designed,a detail analysis about the crashworthiness of three structures,i.e.,the multi-cell conical tube,multi-cell square tapered tube and fourfold-cell conical tube,is made and compared at the condition of keeping the same mass.The multi-cell conical tube has better energy absorption capacity than multi-cell square tapered tube and fourfold-cell conical tube at small load angles.The influences of the internal cell walls,load angle,the cone angle and wall thickness on the performances of crashworthiness are investigated.Multi-objective optimization studies of multiple single load conditions and multiple load conditions were carried out,and the influence of structural parameters on crashworthiness was discussed.The effect of wall thickness on crashworthiness is much greater than the cone angle.However the normalization of average gradients of the cone angle on SEA reached 48.25% compared with the wall thickness when the loading angle is 20°. |
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