局部表面纳米化技术对圆柱壳屈曲模态的诱导及吸能评估

发布时间：2018-06-03 13:22

本文选题：圆柱壳 + 局部表面纳米化　；参考：《大连理工大学》2014年硕士论文

【摘要】：圆柱壳是工程领域中普遍采用的薄壁结构之一。它具有较高的强度、质量轻、低成本、吸能效率高等特点,因此,常常作为吸能结构被广泛应用在汽车、航空航天、船舶等领域,起到缓冲吸能、保护乘员和关键部件的作用。如何提高吸能结构的能量吸收性能已经成为研究人员和工程师非常关注的问题,尤其是在汽车工程领域。本文借助于局部表面纳米化技术,提出一种新的诱导弹塑性圆柱壳屈曲模态的方法。采用有限元计算方法对局部表面纳米化圆柱壳在轴向冲击载荷作用下从屈曲的开始到屈曲的演变整个屈曲过程和屈曲模态变化过程进行数值模拟。通过分析局部表面纳米化后圆柱壳材料性能的改变和表面纳米化分布对圆柱壳屈曲模态的影响,提出三类典型的局部表面纳米化形状分布。这三类局部表面纳米化形状分布分别为：沿圆柱壳轴向呈均匀间隔、等环条带状分布；沿环向呈均匀间隔、等长条带状分布；在圆柱壳表面呈等矩形片状分布等。这些纳米化布局可诱导圆柱壳不同的屈曲模态及发展路径。在此基础上,提出在圆柱壳表面分区段局部表面纳米化布局。所述的区段采用不同的纳米化区域布局设计、不同的纳米化程度,并且在区段间采用特殊的表面纳米化过渡区等。实现冲击载荷小时可控制圆柱壳在设定的区段发生局部屈曲,而冲击载荷大时整体屈曲并分区段逐段屈曲演变。这种方法为控制结构屈曲模态提供了一种设计方法。采用数值模拟的方法研究纳米化区域数目、纳米化区域形状及纳米化程度等对圆柱壳屈曲模态和能量吸收的影响,分析了局部表面纳米化圆柱壳屈曲模态与其吸收能量的关系,并通过分析冲击力位移曲线和利用比吸能等评价指标对圆柱壳的能量吸收性能进行了评估。优化出圆柱壳达到最佳吸能效果(如比吸能最大化)时的各类纳米化区域形状参数和布局参数。同时讨论了圆柱壳长度、厚度及冲击速度等对圆柱壳屈曲变形模式和能量吸收性能的影响。数值模拟结果表明,轴向表面纳米化条带、环向表面纳米化条带和局部片状表面纳米化布局的圆柱壳的屈曲变形模式与能量吸收性能都明显优于原弹塑性圆柱壳。其次,并不是纳米化区域的密集程度越高,变形模式和吸能性能越好。适当的纳米化区域布局可以使圆柱壳屈曲变形模式和吸能性能同时达到最优。分区段表面纳米化布局能够实现圆柱壳分区段渐进屈曲并多次吸收能量。这种设计方法为分层次和分区段能量吸收结构提供一种新的设计思路。
[Abstract]:Cylindrical shell is one of the widely used thin-walled structures in engineering field. It has the characteristics of high strength, light weight, low cost, high energy absorption efficiency and so on. Therefore, it is widely used as energy absorption structure in automobile, aerospace, ship and other fields. It plays the role of cushioning energy absorption, protecting occupants and key components. How to improve the energy absorption performance of energy absorption structures has become a problem that researchers and engineers pay close attention to, especially in the field of automobile engineering. In this paper, a new method for inducing buckling modes of elastic-plastic cylindrical shells is proposed by means of local surface nanocrystalline technique. The finite element method is used to simulate the whole buckling process and the buckling mode change process of the nanocrystalline cylindrical shells subjected to axial impact loading from the beginning of buckling to buckling. By analyzing the change of material properties and the effect of surface nanocrystalline distribution on buckling mode of cylindrical shells after local surface nanocrystallization, three typical local surface nanocrystalline shape distributions are proposed. The nanocrystalline distribution of these three types of local surfaces are as follows: uniform spaced along the axial direction of cylindrical shell, uniform spaced along the circumferential direction, equilong strip distribution, and uniform rectangular flake distribution on the surface of cylindrical shell, etc. These nanostructures can induce different buckling modes and development paths of cylindrical shells. On this basis, the nanocrystalline arrangement of the local surface on the cylindrical shell surface is proposed. The section is designed with different nanocrystalline area layout and different nanocrystalline degree, and special surface nanocrystalline transition zone is used among the sections. The local buckling of cylindrical shells can be controlled when the impact load is small, while the whole buckling evolves step by step when the impact load is large. This method provides a design method for controlling buckling modes of structures. The effects of the number of nanocrystalline region, the shape of nanocrystalline region and the degree of nanocrystalline on the buckling mode and energy absorption of cylindrical shell are studied by numerical simulation. The relationship between the buckling mode of local surface nanocrystalline cylindrical shell and its absorbing energy is analyzed. The energy absorption performance of cylindrical shell was evaluated by analyzing the displacement curve of impact force and using the specific energy absorption index. The shape parameters and layout parameters of nanocrystalline region were optimized when the cylindrical shell achieved the best energy absorption effect (for example, maximum specific energy absorption). The effects of the length, thickness and impact velocity of cylindrical shells on the buckling mode and energy absorption of cylindrical shells are also discussed. The results of numerical simulation show that the buckling mode and energy absorption of cylindrical shells with nanocrystalline axial surface, annular surface nanocrystalline and local sheet surface nanocrystals are better than those of the original elastoplastic cylindrical shells. Secondly, the higher the density of nanocrystalline region, the better the deformation mode and energy absorption performance. The buckling deformation mode and energy absorption performance of cylindrical shells can be optimized by proper nanocrystalline layout. The nanocrystalline layouts of the segmented surfaces can achieve progressive buckling and multiple energy absorption of cylindrical shells. This design method provides a new design idea for hierarchical and segmental energy absorption structures.
【学位授予单位】：大连理工大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TB535;TB306

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