【作者】 王辉；

【导师】 尹汉锋；

【作者基本信息】 湖南大学 ， 机械工程， 2022， 硕士

【摘要】 薄壁多孔结构由于质量轻且具有较优异的吸能效果,应用在各种高速碰撞情形中往往能起到非常好的保护作用。而为了获得具有更好耐撞性的结构,研究人员常通过仿生学,将各种生物中优秀的结构特征引入到仿生设计中。芦苇茎秆质轻且细长中空却能够在湿地环境中抵抗强风而保持直立不折,这说明芦苇茎具有很好的抗弯性能。因此本文将通过研究芦苇茎的微观结构特征并由此设计出具有更好耐撞性能的仿生结构,主要的研究包括以下几个部分:(1)通过准静态三点弯曲实验研究了芦苇茎的抗弯强度,比较发现芦苇茎比其他一些禾本科茎秆具有更高的抗弯强度。然后通过电镜扫描获得芦苇茎横截面和纵截面的微观结构,通过计算机图像处理芦苇横截面发现其细胞组织均为不规则多边形且呈现大小梯度变化的特征,而纵截面上的水平横向细胞壁交错排列。根据芦苇茎微观结构特征,通过编程的方式生成横截面上胞孔大小梯度变化且不规则的多胞结构,纵截面上加入间距不同的隔板,最终设计得到具有芦苇茎微观结构特征的仿芦苇结构。(2)通过定义单元类型、材料本构、边界约束以及接触设置等各种关键字来构建在三点弯曲工况下仿芦苇结构的完整有限元模型。验证了设置对称约束的模型精度,并通过网格灵敏度分析确定模型的网格尺寸。通过3D打印技术制造仿芦苇结构并进行准静态三点弯曲实验。比较实验与仿真,从而检验有限元建模方法的准确性。(3)主要研究了结构不同参数对仿芦苇结构在三点弯曲工况下的耐撞性影响,研究分析了结构的隔板间距系数、结构胞孔壁厚、胞孔梯度变化率、表皮层厚度值以及内圆半径五个参数的变化对结构耐撞性的影响。并且将仿芦苇结构与相同质量下的其他一些仿生结构进行仿真对比,发现所设计的仿芦苇结构具有更好的耐撞性能。(4)将仿芦苇结构的进行拓展应用到车辆-桥墩碰撞实例中,将芦苇茎的结构特征规律运用到桥墩防护中,从而设计出了两块新型的基于仿芦苇结构的桥墩防护结构。同样利用有限元仿真计算分析了新型防护结构在桥墩与车辆碰撞工况中起到的防护效果,与其他的桥墩防护结构相比,基于仿芦苇结构的桥墩防护结构在吸能、减弱冲击以及轻量化方面均有着很好的效果。更多还原

【Abstract】 The thin-walled porous structure always plays an important protector in various high-speed collisions,due to its lightweight and excellent energy absorption.To get better crashworthiness,researchers introduce excellent features from various organisms into bionic structural designs.The reed stalks are light,thin,and hollow,but reeds can resist strong winds and remain upright in the wetland environment,which shows that the reed stalks have good bending resistance.Therefore,this paper will design a biomimetic structure with better crashworthiness by studying the microstructural characteristics of the reed stem.The main research includes the following parts:(1)The bending strength of reed stems was studied by quasi-static three-point bending experiments,and it was found that reed stems had higher bending strength than some other grass stems.Then,the microstructures of the cross-section and longitudinal section of the reed stem were obtained by scanning electron microscope.Through the image processing of the cross-section of reed,it was found that the cell tissues were irregular polygons with the characteristics of graded size,and the arrangement of the horizontal cell walls on the longitudinal section was staggered.According to the microstructural characteristics of the reed stem,irregular cellular structure with the gradient of cell size is generated programmatically in the cross-section,and many partitions with different spacings are added to the longitudinal section.Finally,a novel reed-inspired structure with the microstructural characteristics of the reed stem is designed.(2)The finite element(FE)model of the reed-inspired structure under three-point bending conditions is constructed by defining various keywords such as the element type,material constitutive,boundary constraints,and contact settings.The accuracy of the symmetrically constrained model is verified and the mesh size of the model is determined by mesh sensitivity analysis.The structure fabricated by 3D printing technology is subjected to the quasi-static three-point bending experiment.And the experimental results were compared with simulations to ensure the accuracy of the FE modeling method.(3)The impact of different structural parameters on the crashworthiness of the reed-inspired structure under three-point bending conditions was studied.The influence of five parameters(the coefficient of partition plates spacing,the thickness of cell walls,the gradient of the cell size,the thickness of the epidermis,and the radius of the inner circle)on the crashworthiness of the structure was analyzed.When comparing the reed-inspired structure with some other bionic structures of the same quality,it is found that the reed-inspired structure has better crashworthiness.(4)The reed-inspired structure was extended and applied to the vehicle-pier collision example,and the structural characteristics of the reed stem were applied to the protection of the bridge pier.Two new protections of the bridge pier based on the reed-inspired structure were designed.The protective performance of the new protection in the collision between the pier and the vehicle was analyzed by simulation.Compared with other protection of the pier,the protection based on the reed-inspired structure has a good performance in the energy absorption,reducing impact and light-weight.更多还原