功能密度梯度泡沫铝及其填充结构的吸能性能研究

发布时间：2019-01-05 10:58

【摘要】：功能密度梯度泡沫铝填充锥形薄壁结构是汽车低速碰撞保护中极具应用前景的吸能缓冲结构,为了更好地在受力条件复杂的汽车碰撞中设计和优化泡沫铝填充锥形薄壁结构,进行单轴压缩状态下功能密度泡沫铝填充锥形薄壁结构的试验,并观察其变形模式和吸能机理,同时得到准确的有限元模型是十分必要的;从另一个方面考虑,由于在泡沫铝产品中观察到天然存在的在重力方向上的密度变化,因此,在将泡沫铝应用到汽车吸能结构时,必须充分考虑泡沫铝在重力方向上的密度变化特性对仿真建模的影响以得到准确的有限元模型。为了更好地理解功能密度泡沫铝填充锥形薄壁结构的吸能性能,为设计和优化泡沫铝吸能结构提供直观的依据,本文通过试验观察和仿真分析,对比了截面形状为四边形和六边形的功能密度泡沫铝椎体、铝合金薄壁锥形结构、泡沫铝填充锥形薄壁结构,在单轴准静态压缩工况下的吸能性能。对比项目包括各结构的变形模式、载荷-位移曲线、总吸能量(Absorbed Energy,AE)和比吸能(Specific Absorbed Energy,SAE)。本文使用通用有限元计算程序LS-DYNA进行仿真分析,仿真中的材料模型参数均由其标准材料性能测试试验的结果中拟合提取,其中泡沫铝的材料模型使用的是DeshpandeFleck泡沫材料模型(2000),即LS-DYNA材料卡片MAT_154。本文还使用了Hanssen等(2002)提出的泡沫铝密度模型对本文中使用的泡沫铝材料进行描述,该模型使用泡沫铝三个及以上密度的材料性能参数作为拟合值,得到描述任意密度下材料性能参数的函数。在建立泡沫铝椎体有限元模型时,由于泡沫铝椎体试样的密度分布和变化规律不可知,本文展示了得到准确仿真分析结果的实践性方法和在特定密度变化梯度下不同的建模方法对有限元模型精度的影响。同时为了增强各结构的仿真结果的对比性,在保证仿真精度的前提下,本文在仿真分析中对不同截面形状的泡沫铝椎体模型进行了相同的设置。通过对比各结构的试验和仿真分析变形模式和吸能性能评价参数,本文发现,在单轴准静态压缩工况下,截面形状对泡沫铝椎体和泡沫铝填充锥形薄壁结构的吸能性能影响不大;此外,泡沫铝填充锥形薄壁结构的吸能能力优于单独压缩泡沫铝椎体和薄壁锥形结构的吸能能力的数值和。对具有密度变化的泡沫铝椎体试样建立有限元模型时发现,对泡沫铝椎体的密度分布进行仿真时需要综合考虑泡沫铝标定试验的试样尺寸和密度变化梯度及泡沫铝椎体试样的几何尺寸。
[Abstract]:Function-density gradient aluminum filled tapered thin-walled structure is an energy absorbing buffer structure with great application prospect in automobile low-speed impact protection. In order to better design and optimize foamed aluminum filled conical thin-walled structure in automobile crash with complicated stress conditions. It is necessary to test the conical thin-walled structure filled with functional density aluminum foam under uniaxial compression, observe its deformation mode and energy absorption mechanism, and obtain an accurate finite element model at the same time. On the other hand, because naturally occurring density changes in the gravity direction are observed in aluminum foam products, when applied to automotive energy absorption structures, The influence of density variation in the direction of gravity of aluminum foam on simulation modeling must be fully considered in order to obtain an accurate finite element model. In order to better understand the energy absorption performance of function-density aluminum foam filled conical thin-walled structure and to provide an intuitive basis for the design and optimization of aluminum foam energy absorption structure, this paper is based on experimental observation and simulation analysis. The energy absorption properties of functional density aluminum foam vertebrae with quadrilateral and hexagonal sections, aluminum alloy thin-walled conical structures and aluminum foam filled conical thin-walled structures under uniaxial quasi-static compression are compared. The contrast items include deformation mode, load-displacement curve, total energy absorption (Absorbed Energy,AE) and specific energy absorption (Specific Absorbed Energy,SAE) of each structure. In this paper, the general finite element program LS-DYNA is used to simulate and analyze the parameters of the material model. The parameters of the material model are extracted from the results of the test of the performance of the standard material. The material model of aluminum foam is DeshpandeFleck foam material model (2000), that is, LS-DYNA material card MAT_154. This paper also uses the foam aluminum density model proposed by Hanssen et al. (2002) to describe the aluminum foam materials used in this paper. The model uses the material properties of three or more densities of aluminum foam as the fitting value. A function describing the properties of materials at any density is obtained. When the finite element model of foam aluminum vertebra is established, the density distribution and variation law of foam aluminum vertebral body are unknown. In this paper, the practical methods to obtain accurate simulation results and the influence of different modeling methods on the accuracy of the finite element model under the specific density gradient are shown. At the same time, in order to enhance the comparison of the simulation results of each structure, under the premise of ensuring the simulation accuracy, the same setting of the foam aluminum vertebral body model with different cross-section shape is carried out in this paper. By comparing the experimental and simulation analysis of different structures, it is found that under the uniaxial quasi-static compression condition, the deformation mode and the energy absorption performance evaluation parameters are analyzed. The shape of section has little effect on the energy absorption performance of foamed aluminum vertebrae and foamed aluminum filled conical thin-walled structure. In addition, the energy absorption capacity of aluminum foam filled conical thin-walled structure is better than that of compression foam aluminum vertebra and thin-walled conical structure. The finite element model of foam aluminum vertebrae with density change is found. When simulating the density distribution of foam aluminum vertebrae, it is necessary to consider the sample size and density change gradient of foam aluminum calibration test and the geometric dimension of foam aluminum vertebral sample.
【学位授予单位】：湖南大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TG146.21;TB383.4

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