蜂窝陶瓷催化臭氧氧化处理饮用水中试

在北京市某净水厂进行了臭氧催化氧化处理滤后水的中试，对各种操作条件下蜂窝陶瓷催化臭氧氧化／颗粒活性炭过滤工艺的净水效果进行了考察。结果表明，与臭氧单独氧化相比，臭氧催化氧化反应器中有较高的溶解性臭氧浓度，对天然有机物（NOM）及总有机物（TOC）的去除效果较好，三氯甲烷生成潜能（CHCl3FP）较低。臭氧催化氧化的后续活性炭滤柱上的生物量较多，出水TOC、UV254及CHCl3FP值也均低于臭氧单独氧化的后续活性炭滤柱出水。     

Behavior of intact and damaged honeycombs: a finite element study

The Young’s moduli, the elastic buckling strength and the plastic collapse strength of regular honeycombs with defects consisting of missing cells in the structure were analyzed using the finite element method. The behavior of intact honeycombs was first analyzed; the results of this numerical study are consistent with those of previous analyses. The effect of single, isolated defects of varying sizes and the effect of the separation distance between two defects on the elastic and plastic behaviors were then analyzed. Single, isolated defects reduce the modulus and strength. The elastic buckling strength of a honeycomb with a defect normalized by the intact strength decreases directly with the ratio of the minimum net cross-sectional area normalized by the intact cross-sectional area. The plastic collapse strength of a honeycomb with a defect normalized by the intact strength decreases less rapidly than the ratio of the minimum net cross-sectional area normalized by the intact cross-sectional area. Two closely spaced, separate defects interact to reduce the elastic buckling strength of a honeycomb; at a separation distance of about ten cells separate defects act independently. The separation distance between two defects has little effect on the Young’s modulus or the plastic collapse strength of a honeycomb. The finite element analysis allows localization behavior to be studied: we find that the localization strain decreases with increasing .     

Post-collapse characteristics of ductile circular honeycombs under in-plane compression

The post-collapse behaviour of a circular honeycomb material under in-plane compression is analysed in order to estimate the effect of the structural topology on the material strength. A structural approach using the limit analysis and the concept of an equivalent structure is employed to describe the large plastic deformations during post-collapse process. Based on some published experimental results (International Journal of Solids Structures 36 (1999) 4367–996) and our numerical simulations, certain deformation patterns are constructed depending on the direction of loading, and the corresponding post-collapse load-carrying capacities during large deformation until densification of cells are presented.The present analysis shows that the post-collapse stress associated with an equi-biaxial compression is not excessively larger than the corresponding uniaxial stresses, in contrast to those of hexagonal honeycombs in response to biaxial loading. This behaviour is attributed to the different deformation mechanism as the curvature of a cell wall invokes bending without stretching.The influence of the size of the connecting segment between two neighbouring cells is studied, showing that the “shape” of the limit surface varies significantly depending on this connection.     

基材属性对铝蜂窝共面力学性能的影响

目的研究不同属性的基体材料对铝蜂窝共面压缩力学性能的影响。方法在保持正六边形蜂窝结构参数不变的情况下,改变基材属性,基体材料模型分别选择不同应变强化参数的双线性各向同性强化模型和理想弹塑性模型,建立相关可靠的有限元模型并进行大量的模拟计算。获得相应的变形模式和应力-应变曲线,对曲线进一步处理得到蜂窝共面静动态峰应力,并将结果以图表形式展示并分析。结果随着冲击速度的增加,样品依次出现了"X","V","一"字型3种变形模式,基体材料的应变强化效应使变形趋于均匀化;基体材料的应变强化效应显著增加了蜂窝的静态峰应力,对动态峰应力增量的影响可以忽略,对计算数据处理后得到了应变强化参数与动态峰应力的计算公式。结论基材具有强化特性的蜂窝,其共面静态力学性能优于基材为弹性理想塑性材料模型的蜂窝;在利用数值模拟的方法来研究蜂窝结构共面静态力学行为时,需要考虑基体材料的强化效应。     

蜂窝状ZnCo2O4的制备及对AP和CL-20热分解行为的影响

为了研究双金属氧化物在固体推进剂中的催化性能,采用溶剂热法及热退火工艺成功制备出在镍泡沫(NF)上生长的蜂窝状ZnCo_2O_4(honeycombs ZnCo_2O_4,ZnCo_2O_4(HCs)),并通过X射线粉末衍射(XRD),X射线光电子能谱仪(XPS),傅里叶红外光谱仪(FT-IR),扫描电子显微镜(SEM)及N2吸附-脱附测试对其物相组成和形貌结构进行了表征分析。采用差示扫描量热法(DSC)研究了制备的ZnCo_2O_4(HCs)对高氯酸铵(AP)和六硝基六氮杂异伍兹烷(CL-20)的催化性能。结果表明,当ZnCo_2O_4(HCs)用量为20%时,ZnCo_2O_4(HCs)/AP和ZnCo_2O_4(HCs)/CL-20最低热分解峰温,分别为575.01,521.55 K。与纯AP和CL-20相比,ZnCo_2O_4(HCs)/AP和ZnCo_2O_4(HCs)/CL-20复合物的放热分解峰温分别提前了101.87,3.73 K,热分析动力学计算表明它们的表观活化能分别降低了17.88,6.23 kJ·mol~(-1)。与文献报道的纳米微晶状(NCs)、纳米线状(NWs)及纳米球状(NSs)ZnCo_2O_4相比,蜂窝状ZnCo_2O_4呈现出良好的催化活性,这可归因于ZnCo_2O_4(HCs)的多孔结构和大比表面积,能够为热分解反应提供丰富的活性位点。     

结构参数对自相似多级蜂窝力学性能的影响

对蜂窝的代表性体积单元(RVE)研究发现,相比于均匀化边界条件,周期性边界条件能更好地预测蜂窝的等效力学性能。基于周期性边界条件,对自相似多级蜂窝进行面内不同方向的拉伸模拟,重点分析了蜂窝孔隙率与多级长度比对拉伸性能的影响。结果表明:自相似多级蜂窝在拉伸过程中会呈现面内各向异性,沿扶手椅方向拉伸时,会在节点六边形的水平连接边处发生断裂;沿锯齿形方向拉伸时,当节点六边形的边长大于壁厚和节点六边形的连接斜边的边长较长的情况下,蜂窝会出现两次拉伸破坏,分别在节点六边形边与节点六边形的连接斜边处,而在其他情况下,则只会在节点六边形连接斜边处发生一次破坏。并且自相似多级蜂窝随着孔隙率或长度比的增大,蜂窝拉伸强度呈现减小的趋势。     

Ductile fracture of two-dimensional cellular structures – Dedicated to Prof. Dr.-Ing. D. Gross on the occasion of his 60th birthday

Crack growth initiation and subsequent resistance to propagation are explored numerically for regular and irregular hexagonal honeycomb structures made from ductile cell walls. The elasto-plastic response of the cell walls is described by a bilinear uniaxial stress-strain law, with fracture of the cell walls characterised by the fracture energy per unit area. Estimates for the macroscopic toughness and the associated plastic zone shape are derived analytically on the basis of simple considerations. Crack propagation is simulated numerically by fracturing elements within a finite element model and K-resistance curves are calculated under the assumption of small-scale yielding. The dependence of the crack growth behaviour upon the cell wall material parameters and geometric imperfections of the structure is investigated.     

92负刚度蜂窝结构压缩性能分析

为准确开展以黏弹性材料为载体的负刚度蜂窝结构数值模拟研究,提出一种基于黏弹性广义Maxwell模型的负刚度蜂窝结构压缩性能数值模拟法。进行了尼龙12的动态机械分析(DMA)测试,基于广义Maxwell模型拟合实测动态模量数据,得到反映尼龙12动态黏弹性的无量纲模量g_i和松弛时间τ_i。建立了负刚度蜂窝结构的有限元模型,基于实测的动态黏弹性参数,进行压缩性能的数值模拟研究,并同压缩试验结果进行比较,验证了数值模拟的准确性,利用数值模拟研究几何参数对结构压缩性能的影响规律。结果表明,基于黏弹性广义Maxwell模型的负刚度蜂窝结构数值模拟分析法可较准确模拟结构的压缩性能,为预测负刚度蜂窝结构的力学性能提供帮助。     

Multifunctional design of prismatic cellular materials

Low density, prismatic cellular materials have a combination of properties that make them suitable for multifunctional or multi-physics applications such as ultralight load-bearing combined with energy absorption and heat transfer. In this work, non-uniform, graded cellular materials are designed to achieve superior thermal and structural performance. A general multifunctional design approach is presented that integrates multiobjective decision-making with multi-physics analysis tools of structural and heat transfer performance. Approximate analysis models for heat transfer and elastic stiffness are utilized to analyze designs efficiently. Search/solution algorithms are used to solve multiobjective decisions by interfacing with customized and commercial software. During the design process, cell topology is assumed to be rectangular, but aspect ratios and dimensions of cells and cell walls are varied. Two design scenarios are considered – maximum convective heat transfer and in-plane elastic stiffness in the first case and maximum convective heat transfer and elastic buckling strength in the second case. A portfolio of heat exchanger designs is generated with both periodic and functionally graded cells. Both single- and multi-objective performance are considered, and trade-offs are assessed between thermal and structural performance. Generalization of this approach is discussed for broader materials design applications in which material structures and processing paths are designed to achieve targeted properties and performance characteristics within a larger overall systems design process, and process-structure-property-performance relations are manifested on a hierarchy of length and time scales.     

纸蜂窝压缩密实化应变评估

分析纸蜂窝压缩密实化应变对纸蜂窝吸能特性评估的重要性,引入纸蜂窝压缩瞬时相对密度的概念,从理论上建立纸蜂窝压缩密实化应变评估方程,并做了不同结构参数的纸蜂窝准静态压缩试验,试验结果表明纸蜂窝胞壁厚度、边长和纸蜂窝的拉伸率等结构因素对压缩密实化应变均有一定的影响:纸蜂窝压缩密实化应变随胞壁的厚度δ的增大而减小;随蜂窝胞元边长ι的增大而增大:随蜂窝胞壁厚跨比δ/ι的增大而减小;随其拉伸率γ的增大,先增大后减小,在拉伸率为1时,其压缩密实化应变达最大值;纸蜂窝结构因素对其压缩密实化应变的影响与文中的理论公式是相符的,纸蜂窝的密实化应变与其相对密度近似呈反比例关系,当纸蜂窝的瞬时相对密度为0.39左右时,纸蜂窝压缩趋于密实化.将该评估方程用于五层瓦楞纸板的压缩密实化过程评估表明它也可用于其他结构形式纸蜂窝材料的压缩密实化应变评估,具有一定的普适性.