【作者】 龚超；

【导师】 白中浩；

【作者基本信息】 湖南大学 ， 机械工程， 2022， 博士

【摘要】 近年来,随着我国的汽车保有量逐年增加,交通事故的发生也愈加频繁。汽车出行给人们带来便捷的同时也对其生命和财产构成极大威胁。因此,车身结构耐撞性设计与研究成为当下的重点课题。同时,新能源汽车的快速发展,对车身轻量化提出了更高的要求,这对车身结构耐撞性设计也是一个极大的挑战。金属薄壁结构由于其优异的能量吸收性能被广泛应用于车身结构设计中。然而现有的金属薄壁结构存在能量吸收效率较低、载荷稳定性较差等不足,要进一步提升其吸能能力,深入分析其吸能机理揭示其吸能能力的关键影响因素并提出相应设计准则势在必行。此外,现有的薄壁结构的设计大多依赖于设计人员的经验进行设计,效率较低。自然界的生物结构经过数万年的进化使其具有优良的承受载荷能力,对自然生物结构进行仿生设计可以极大提高设计效率。因此,仿生设计近年来成为各个工程应用领域的研究热点。本文通过对自然生物结构的宏观和微观特征进行结构仿生,提出了四种新型仿生多胞薄壁结构的设计方法,并对其吸能机理和耐撞性表现进行了系统研究。主要研究内容与创新点如下:(1)通过对薄壁吸能结构的吸能机理的分析,提出了多胞薄壁结构的设计准则。首先,基于简化超折叠单元理论和组成单元法,对多胞薄壁结构的吸能机理进行了深入分析并揭示出影响其吸能能力的关键因素,然后,进一步提出多胞薄壁结构的设计准则。这些设计准则对提高多胞薄壁结构的设计效率具有重要意义,也为进一步对仿生多胞薄壁结构的设计方法研究提供了理论指导。(2)受荷叶叶脉的结构特征启发,提出了一种仿生荷叶多胞薄壁圆管的设计方法。首先,根据荷叶叶脉的分叉结构提出了仿生荷叶多胞管,建立相应的有限元模型,通过对仿生荷叶多胞管试件进行准静态压缩试验来验证有限元模型的准确性和可靠性,试验结果与仿真模拟结果吻合地较好。基于简化超折叠单元理论对仿生荷叶多胞管的平均压溃力和比吸能的理论模型进行了推导,并基于得到的理论模型对其吸能机理进行了揭示。进而通过所建立的有限元模型研究了仿生荷叶多胞管的截面几何参数对其耐撞性能影响;通过对仿生荷叶多胞管进行多目标优化得到了最佳的截面参数配置。研究结果表明,与传统的多胞薄壁管相比,仿生荷叶多胞管具有更出色的耐撞性表现。(3)受植物茎的生物进化规律启发,提出了一种仿生梯度多胞薄壁结构的设计方法。首先,对植物茎进化过程中凸显的梯度特征进行结构仿生,提出了一种仿生梯度多胞结构。然后,基于简化超折叠单元理论对仿生梯度多胞管的平均压溃力和比吸能的理论预测模型进行了推导,对其吸能机理进行了揭示。进一步地,建立了仿生梯度多胞管的有限元模型,并开展了相关的准静态压溃试验来验证仿生梯度多胞管有限元模型的可靠性。结果表明,仿生梯度多胞管的仿真模拟结果与试验测试结果基本吻合。进一步研究了关键几何参数对仿生梯度多胞管耐撞性的影响,结果表明,层数和壁厚对仿生梯度多胞管的耐撞性能有显著影响。所推导的仿生梯度多胞管平均压缩力和比吸能的理论预测模型的精度通过与仿真结果对比得到了有效验证。仿生梯度多胞管与传统多胞圆管相比耐撞性能大大提升,该研究对多胞薄壁结构的耐撞性设计提供了很好的参考。(4)受生物层级结构的启发,提出了一种基于顶点的层级多胞方管的设计方法。首先,通过改变常规多胞方管的胞元的连接方式提出了一种新型多胞方管,进而提出了一种基于顶点的层级多胞方管。然后,基于简化超折叠单元理论推导了平均压溃力和比吸能的理论预测模型,并基于理论预测模型将新型多胞方管和基于顶点的层级多胞方管与相应的传统多胞方管进行对比来分析其耐撞性优势。进一步地,建立了新型多胞方管和基于顶点的层级多胞方管的有限元模型并对模型精度进行了试验验证。然后从仿真的角度通过与相应传统多胞管进行对比分析了新型多胞方管和基于顶点的层级多胞方管的变形模式和能量吸收机理。结果表明,理论和仿真分析的结果均有力证明了所提出的多胞方管截面配置方法比传统的配置方法更高效,且基于顶点的层级多胞方管是一种高效的薄壁吸能结构。(5)受生物层级结构启发,提出了一种基于边的层级多胞方管的设计方法。首先,建立了基于边的层级多胞方管的有限元模型并对其进行了试验验证,有限元仿真结果和试验结果吻合较好,有限元模型得到有效验证。进一步地,用建立的有限元模型对基于边的层级多胞方管的耐撞性能进行了研究,并研究了层级等级对基于边的层级多胞方管耐撞性的影响;研究表明,与传统多胞方管相比,基于边的层级多胞方管的耐撞性能有了很大的提升,且层级等级对基于边的层级多胞方管的能量吸收效率具有显著影响。最后,基于简化超折叠单元理论对基于边的层级多胞方管的平均压溃力和比吸能的理论预测模型进行了推导,并基于理论预测模型对基于边的层级多胞方管的能量吸收特性进行了理论分析,从理论的角度揭示了基于边的层级多胞方管的吸能机理和吸能优势。研究结果表明,仿生层级结构的引入明显地提升了多胞薄壁方管结构的耐撞性能。本文基于对自然生物结构的宏观和微观特征进行仿生,提出了四种仿生多胞薄壁吸能结构,经研究证明其具有非常优异的耐撞性能。这些仿生多胞薄壁吸能结构可以应用到新能源汽车前纵梁和底部横梁的设计开发中,对降低乘员在汽车正面碰撞中的损伤具有重要作用。同时,本文的研究也为仿生设计方法在结构耐撞性设计中的深入应用具有重要的参考意义。更多还原

【Abstract】 In recent years,with the gradual increase of car parc in our country,the occurrence of traffic accidents has become more and more frequent.Car travel not only brings convenience to people,but also poses a great threat to t heir lives and property.Therefore,the research on the crashworthiness design of the body structure has become a key topic at present.At the same time,the rapid development of new energy vehicles has put forward higher requirements for the lightweight of the body,which is also a great challenge to the crashworthiness design of the body structure.Metal thin-walled structures are widely used in body structure design due to their excellent energy absorption properties.However,the existing metal thin-walled structures have shortcomings such as low energy absorption efficiency and poor load stability.To further improve their energy absorption capacity,in-depth analysis of their energy absorption mechanism reveals the key factors affecting its energy absorption capacity and proposes corresponding designs guidelines are imperative.In addition,the design of the existing thin-walled structure mostly relies on the experience of the designer,and the design efficiency is low.After thousands of years of evolution,natural biological structures have excellent load bearing capacity,and the bionic design of natural biological structures can greatly improve the design efficiency.Therefore,bionic design has become a research hot spot in various engineering application fields in recent years.In this paper,through the biomimetic design of the macroscopic and microscopic characteristics of natural biological structures,four novel design methods of biomimetic multi-cell thin-walled structures are proposed,and their energy absorption mechanism and crashworthiness performance are systematically studied.The main research focuses and innovations are as follows:(1)By analyzing the energy absorption mechanism of thin-walled energyabsorbing structures,the design criteria of multi-cell thin-walled structures are proposed.Firstly,based on the simplified super folding element theory and the constituent element method,the energy absorption mechanism of the multi-cell thin-walled structure was deeply analyzed and the key factors affecting its energy absorption capacity were revealed.Then,the design guidelines of the multi-cell thin-walled structure was further proposed.The analysis of the energy absorption mechanism of thin-walled structures can reveal the essence of its energy absorption behavior,so as to further explore its energy absorption potential,which is of great significance for improving the design efficiency of multi-cell thin-walled structures,and also for further research on bionic multicellular structures.The research provides theoretical guidance on the design method of thin-walled structures.(2)Inspired by the structural characteristics of lotus leaf veins,a design method of bionic lotus leaf multi-cell thin-walled circular tubes is proposed.Firstly,according to the bifurcation structure of the lotus leaf vein,a bionic lotus leaf multi-cell tube is proposed and the corresponding finite element model is established.The accuracy and reliability of the finite element model are verified by quasi-static compression test of the bionic lotus leaf multicellular tube specimen.The test results are in good agreement with the simulation results.Based on the simplified super folding element theory,the theoretical models of the mean crushing force and specific energy absorption of the bionic lotus multi-cell tube were deduced.And the energy absorption mechanism was revealed based on the obtained theoretical model.Furthermore,the effects of the cross-sectional geometric parameters of the bionic lotus multicell tube on its crashworthiness was studied through the established finite element model;the optimal cross-sectional parameter configuration was obtained through multi-objective optimization of the bionic lotus multi-cell tube.The research results show that the bionic lotus multi-cell tube has better crashworthiness performance than that of the traditional multi-cell thin-walled tube.(3)Inspired by the biological evolution law of plant stems,a design method of bionic gradient multi-cell thin-walled structure is proposed.Firstly,a bionic gradient multi-cell thin-walled structure was proposed by structural biomimetic of the gradient features highlighted in the evolution of plant stems.Then,the theoretical prediction model of the mean crushing force and specific energy absorption of the bionic gradient multi-cell thin-walled tube was deduced based on the simplified super folding element theory.And its energy absorption mechanism was revealed.Furthermore,the finite element model of the bionic gradient multi-cell thin-walled tube was established,and the corresponding quasi-static compression test was carried out to verify the reliability of the established finite element model.The results show that the simulation results of the bionic gradient multi-cell thin-walled tube are basically consistent with the experimental test results.The effects of key geometric parameters on the crashworthiness of the bionic gradient multi-cell thin-walled tube was further studied,and the results showed that the number of layers and wall thickness had a significant effects.The accuracy of the theoretical prediction model of the mean crushing force and specific energy absorption of the bionic gradient multi-cell thin-walled tube is effectively verified by comparing with the simulation results.Compared with the traditional multi-cell circular tube,the bionic gradient multi-cell thin-walled tube has greatly improved crashworthiness performance.This study provides a good reference for the crashworthiness design of the multi-cell thin-walled structure.(4)Inspired by the bionic hierarchical structure,a design method of a vertex-based hierarchical multi-cell square tube is proposed.Firstly,a novel multi-cell square tube is proposed by changing the connection mode of the cells of the conventional multi-cell square tube,and then a vertex-based hierarchical multi-cellular square tube is proposed.Then,the theoretical prediction models of the mean crushing force and specific energy absorption are derived based on the simplified super folding element theory.Based on the theoretical prediction model,the crashworthiness advantages of the novel multi-cell square tube and the vertex-based hierarchical multi-cell square tube are revealed by compared with the corresponding traditional multi-cell square tube.Furthermore,the finite element models of the novel multi-cell square tube and the vertex-based hierarchical multi-cell square tube are established and the model accuracy is verified by experiments.Then,the deformation mode and energy absorption mechanism of the novel multi-cell square tube and the vertex-based hierarchical multi-cell square tube are compared with the corresponding traditional multi-cell square tube from the point of simulation.The results show that both theoretical and simulation analysis results strongly prove that the proposed cross-section configuration method of multi-cell square tube is more efficient than that of traditional method,and the vertex-based hierarchical multi-cell square tube is an efficient energy-absorbing thin-walled structure.(5)Inspired by the bionic hierarchical structures,an design method of the edge-based hierarchical multi-cell square tubes is proposed.First,the finite element model of the edge-based hierarchical multi-cell square tube is established and verified by experiments.The simulation results are in good agreement with the experimental results,and the finite element model is effectively verified.Further,the crashworthiness performance of the edge-based hierarchical multi-cell square tube was studied with the established finite element model,and the effects of the hierarchical level on the crashworthiness of the edge-based hierarchical multi-cell square tube was studied.Compared with the traditional multi-cell square tube,the crashworthiness performance of the edge-based hierarchical multi-cell square tube has been greatly improved,and the hierarchical level has a significant effect on the energy absorption efficiency of the edge-based hierarchical multi-cell square tube.Finally,the theoretical prediction model of the mean crushing force and specific energy absorption of the edge-based hierarchical multi-cell square tube is deduced based on the simplified super folding element theory.Based on the theoretical prediction model,the energy absorption characteristics of the edge-based hierarchical multi-cell square tube were theoretically analyzed,and the energy absorption mechanism and energy absorption advantages of the edge-based hierarchical multi-cell square tube were revealed from the theoretical point of view.The research results show that the introduction of the bionic hierarchical structure significantly improves the crashworthiness of the multicell thin-walled square tube.In this paper,four biomimetic multicellular thin-walled energy-absorbing structures are proposed based on the bionics of the macro and microscopic features of natural biological structures,which have been proved to have excellent crashworthiness performance.These bionic multi-cell thin-walled structures can be applied to the design and development of the front longitudinal beams and bottom cross beams of new energy vehicles,and play an important role in reducing the damage of occupants in frontal collisions of vehicles.At the same time,the research in this paper also has important reference significance for the in-depth application of the bionic design method in the structural crashworthiness design.更多还原