蜂窝铝材料面内尺寸效应及应变率影响研究

发布时间：2018-08-29 15:02

【摘要】：由于六边形蜂窝结构具有一系列优良特性且应用广泛,有必要对其进行全面了解,实际应用中常常被设计成面外和面内两个方向承受载荷,且多胞材料的性能与尺寸有很大相关性,尤其是面内胞元个数的改变对结构力学性能的影响需要进一步细化研究。因此,面内尺寸的改变在面内压缩时对试件力学参数的影响作为本文主要研究内容。在面内压缩中,无尺寸效应影响情况下,应变率对变形模态以及力学性能的影响也是我们关心的重点。本文通过试验及数值模拟研究了面内压缩时面内尺寸效应对试件力学性能的影响,以及不同应变率对变形模态和力学性能的影响:通过英斯特朗材料试验机对3种相对密度、6种面内尺寸共计18种六边形铝蜂窝块体试件,分别从x1和x2方向进行面内单轴压缩实验,发现不同面内尺寸、不同密度蜂窝铝试件在面内单轴压缩过程中变形模式相同,都为逐层周期性叠加直到压实。对于力学性能方面,三种密度蜂窝铝试件的密实化应变均没有对面内尺寸表现出明显的尺寸效应,可以认为密实化应变是一个稳定的力学参数;而宏观刚度在x1和x2方向压缩时都表现出了对面内尺寸的敏感性,并随着试件尺寸的增加而增大直到N×N=9×9时趋于稳定;相对密度较小(t/D=0.016)的试件平台应力随着面内尺寸的增加而增大直到n×n=11×11时趋于稳定,而对于t/d=0.026和0.02两种试件的平台应力对于试件尺寸并不敏感;最后引入薄弱边界层理论合理解释了试件刚度在相对密度较小的情况下对面内尺寸减小变得更为敏感的原因,通过理论公式推导和实验数据对比验证了引用合理性;总之,在面内受力的蜂窝材料使用中,为得到不受面内尺寸效应影响的具有稳定力学参数的材料,应该选择胞元尺寸至少为n×n=11×11。然后采用abaqus有限元软件,分别从x1和x2方向进行面内准静态单轴压缩数值模拟,分析变形模态以及平台应力和密实化应变受面内尺寸效应的影响。结果与实验相同,进而验证了模型的可靠性。由上面对模型可靠性分析作为保障,采用abaqus有限元软件,为不受尺寸效应影响,建立相对密度t/d=0.016胞元尺寸为n×n=11×11的蜂窝铝材料模型,分别进行从x1和x2方向进行面内准静态单轴压缩数值模拟。发现不同应变率对变形模态有明显影响,在x1方向准静态及中等应变率压缩时试件横向对称轴附近胞元壁相互接触呈“一”字型逐层叠加,直至试件完全密实化。x2方向准静态及中等应变率压缩时试件中心区域发生塑性变形,胞元以非对称剪切变形模型破坏,然后胞壁呈三角形叠加并挤压相邻胞元,随着进一步压缩逐层塑性叠加直至完全密实化。高应变率时,两方向变形模态转变为冲击变形,惯性效应明显,上承载面随着压板的加载向下“i”型逐层叠加密实化。x1及x2方向压缩时应变率由准静态到低动态再到冲击状态下的平台应力均呈明显上升趋势,表现出较强应变率敏感性;而在x2方向压缩中密实化应变只在应变率达到500前有较小幅度的上升,之后在0.8附近波动,x1方向压缩时密实化应变没有随应变率的增加而变化,而是在0.85附近波动。所以蜂窝铝材料为应变率敏感材料。
[Abstract]:Because hexagonal honeycomb structures have a series of excellent characteristics and are widely used, it is necessary to have a comprehensive understanding of them. In practical applications, they are often designed to bear loads in both out-of-plane and in-plane directions, and the properties of polycellular materials are highly correlated with the size, especially the effect of the number of in-plane cells on the mechanical properties of structures. Therefore, the effect of in-plane dimension change on mechanical parameters of specimens during in-plane compression is the main content of this paper. In in-plane compression, the effect of strain rate on deformation mode and mechanical properties is also the focus of our attention without the influence of size effect. The effect of in-plane dimension on the mechanical properties of specimens under in-plane compression and the effect of different strain rates on the deformation modes and mechanical properties were investigated. The deformation modes of honeycomb aluminum specimens with different in-plane sizes and densities are the same during in-plane uniaxial compression, which are periodically superimposed layer by layer until compaction. The macro-stiffness is sensitive to the in-plane dimension when the specimen is compressed in the directions of x_1 and x_2, and tends to be stable when the specimen size increases until N N = 9 9, and the plateau stress of the specimen with smaller relative density (t/D = 0.016) increases with the in-plane dimension until n n = 11 11. The platform stress of t/d=0.026 and 0.02 specimens is not sensitive to the size of the specimens. Finally, the weak boundary layer theory is introduced to explain the reason why the stiffness of the specimens becomes more sensitive to the reduction of the in-plane size when the relative density is small. In the use of honeycomb materials subjected to in-plane force, in order to obtain materials with stable mechanical parameters which are not affected by in-plane size effect, the cell size should be at least n*n=11*11. Then the in-plane quasi-static uniaxial compression numerical simulation should be carried out by using ABAQUS finite element software from x_1 and x_2 directions, respectively, to analyze deformation modes and platform stress. The results are the same as those of the experiments, which verify the reliability of the model. Based on the above reliability analysis and ABAQUS finite element software, a honeycomb aluminum material model with relative density t/d=0.016 and cell size n*n=11*11 is established to avoid the influence of size effect. In-plane quasi-static uniaxial compression was numerically simulated in the directions of x_1 and x_2. It was found that different strain rates have obvious effects on the deformation modes. Under quasi-static and moderate strain rate compression in the direction of x_1, the cell walls near the transverse symmetric axis of the specimen were stacked layer by layer until the specimen was fully compacted. When the strain rate is high, the deformation modes of the two directions change to impact deformation, and the inertia effect is obvious, and the upper bearing surface is obvious. The strain rate increases obviously from quasi-static state to low dynamic state and then to impact state, showing a strong strain rate sensitivity, while the compacted strain increases only slightly before the strain rate reaches 500 in the direction of x2 compression. Then it fluctuates around 0.8, and the densification strain does not change with the increase of strain rate, but fluctuates around 0.85. So honeycomb aluminum is a strain rate sensitive material.
【学位授予单位】：太原理工大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TB383.4

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