含有序孔洞的多孔氧化铝薄膜的力学性能测量和数值模拟

高纯铝箔在特定的溶液下经过电化学阳极氧化腐蚀,可在其表面生成一层多孔的非晶氧化铝层,其孔径分布非常均匀,孔大致呈六方密排布。由于此类薄膜具有规则的纳米级孔径,大的比表面积,良好的自组织排列性,所以其日益受到人们的关注。然而,到目前为止,对于此类薄膜力学性能的研究还很少,所以在一定程度上限制其功能的开发和应用。为了获得此类多孔膜的弹性常数,本文首先由实验出发,通过光力学检测(双光束散斑干涉)的方法得到薄膜拉伸时的整体表观弹性模量。然后对薄膜建立二维有限元模型,运用均匀化理论反推出其基体(无孔结构)的弹性模量,同时考察了不同的基体泊松比对模型整体表观模量的影响,并且用一般有限元方法验证了沿特定方向拉伸时均匀化模型计算的有效性。     

鼓膜法测定纳米多孔氧化铝薄膜的弹性模量

本文的多孔氧化铝薄膜含有直径均一、互相平行且与表面垂直的有序纳米孔阵列。它有广阔的应用前景。多孔氧化铝膜与氧化铝陶瓷材料的宏观力学性能有很大的区别。本文用鼓膜法结合实时电子散斑干涉(ESPI)技术,测量薄膜压力与离面位移的关系,再用周边固支平板小挠度模型计算出多孔氧化铝薄膜的宏观弹性模量。本实验中厚76微米的多孔氧化铝薄膜的宏观弹性模量为32.5GPa,比热压氧化铝陶瓷的弹性模量几乎小一个数量级,主要是由于晶相和细观结构不同造成的。这种方法较适合测量此类结构薄膜的力学性能。     

含有序孔洞的多孔氧化铝薄膜的弹性模量测量

高纯铝箔在特定的溶液下经过电化学阳极氧化腐蚀,可在其表面生成一层多孔的非晶氧化铝层,孔大致呈六方密排,孔径分布均匀.此类薄膜具有规则的纳米级孔径,大的比表面积,可用在微纳滤方面和纳米材料组装方面.然而,对于此类薄膜力学性能的研究较少,在一定程度上限制其功能的开发和应用.为了获得此类多孔膜的弹性常数,本文用鼓膜法结合散斑干涉实验方法、单轴拉伸结合双光束干涉法和多普勒测振仪三种方法测量氧化铝多孔膜的弹性模量,得到的宏观弹性模量基本相同, 并对三种方法的优缺点进行了比较,分析了多孔氧化铝膜与块状氧化铝材料或致密氧化铝膜力学性能的差异.     

含有序孔洞的多孔氧化铝薄膜的弹性模量测量

高纯铝箔在特定的溶液下经过电化学阳极氧化腐蚀，可在其表面生成一层多孔的非晶氧化铝层，孔大致呈六方密排，孔径分布均匀。此类薄膜具有规则的纳米级孔径，大的比表面积，可用在微纳滤方面和纳米材料组装方面。然而，对于此类薄膜力学性能的研究较少，在一定程度上限制其功能的开发和应用。为了获得此类多孔膜的弹性常数，本文用鼓膜法结合散斑干涉实验方法、单轴拉伸结合双光束干涉法和多普勒测振仪三种方法测量氧化铝多孔膜的弹性模量，得到的宏观弹性模量基本相同，并对三种方法的优缺点进行了比较，分析了多孔氧化铝膜与块状氧化铝材料或致密氧化铝膜力学性能的差并。     

含有序孔洞的多孔氧化铝薄膜的弹性模量测量

高纯铝箔在特定的溶液下经过电化学阳极氧化腐蚀,可在其表面生成一层多孔的非晶氧化铝层,孔大致呈六方密排,孔径分布均匀.此类薄膜具有规则的纳米级孔径,大的比表面积,可用在微纳滤方面和纳米材料组装方面.然而,对于此类薄膜力学性能的研究较少,在一定程度上限制其功能的开发和应用.为了获得此类多孔膜的弹性常数,本文用鼓膜法结合散斑干涉实验方法、单轴拉伸结合双光束干涉法和多普勒测振仪三种方法测量氧化铝多孔膜的弹性模量,得到的宏观弹性模量基本相同, 并对三种方法的优缺点进行了比较,分析了多孔氧化铝膜与块状氧化铝材料或致密氧化铝膜力学性能的差异.

     

氧化铝多孔膜变形的时间序列散斑干涉法检测

本文通过鼓膜实验,利用双光束电子散斑干涉技术(ESPI)和时间序列的散斑干涉法,首先对纯铝试样鼓膜变形进行测量,并结合薄板小挠度理论计算了纯铝的弹性模量,结果与弹性模量的参考值基本相同,表明该测量变形的方法精确可行。在此基础上对二步阳极氧化法制备的氧化铝多孔膜试样的鼓膜变形进行了检测,变形检测结果为进一步研究氧化铝多孔膜的力学性能及其与微观结构的关系提供了依据和基础。     

横观各向同性液体饱和多孔介质中平面波的传播

基于孔隙介质的Ｂｉｏｔ理论,研究了横观各向同性液体饱和多孔介质中平面波的传播特性．首先导出了波传播的特征方程并给出其解析解,结果显示：有４种不同波速的平面体波传播：第一准纵波（ＱＰ１）、第二准纵波（ＱＰ２）、准横波（ＱＳＶ）和反平面横波（ＳＨ）．文中给出了波速和衰减的解析表达式,数值计算了频散曲线和衰减曲线,并讨论了各类准体波位移之间的耦合关系．最后分析了Ｒａｙｌｅｉｇｈ波的生成条件和传播特性．文章详细讨论了介质异性对波传播特性的影响     

横观各向同性热弹性多孔介质板的精化理论

研究了孔隙水压力作用下横观各向同性热弹性多孔介质板的精化理论。在不做任何预先假设的情况下,利用 Lur’e 方法和横观各向同性热弹性多孔介质的通解,得到了横观各向同性热弹性多孔介质板的精化理论。首先,根据调和函数的sin算子函数表达式,得到了用5个二维待定函数表示的位移场和应力场;其次,在非齐次边界条件下,利用基本的数学算法,得到了在孔隙水压力载荷作用下热弹性多孔介质板的精化方程;最后,通过舍弃高阶项,得到了位移场和应力场的近似解。     

锂离子薄膜电极充放电变形的原位实验观测方法

锂离子薄膜电极在充放电过程中的力学变形会严重影响锂离子电池的性能和使用寿命。本文提出一种原位观测锂离子薄膜电极充放电变形的实验方法,该方法通过设计一种新型的实验室模型电池,并采用基于位相增量叠加的相移电子散斑干涉方法测量变形,成功实现了对锂离子薄膜电极充放电变形的原位实验观测。实验结果表明,锂离子薄膜电极在充放电过程中会产生周期性的变形,该变形宏观上与电池的SOC(State of Charge,充电状态)相关,微观上则与锂离子在电极活性材料中的嵌入/脱出过程对应。该实验方法为深入研究锂离子薄膜电极变形对锂离子电池性能的影响提供了一种有力的实验手段。     

纳米压痕法研究PZT压电薄膜的力学性能

PZT压电薄膜的力学性能如弹性模量、硬度等对于MEMS器件的结构设计、结构响应特性、服役性能等尤为重要.薄膜材料由于尺寸效应、表面效应等的作用,力学性能与宏观块体材料有显著差异.本文用纳米压痕法获得了PZT压电薄膜的弹性模量和硬度,考察了基底的影响,分析了退火时间对于其力学性能的影响,以及硬度和压入深度之间的压痕尺度效应.     

Electronic speckle pattern interferometry analysis of tensile tests of semihard copper sheets

Uniaxial tension tests of semihard copper sheets were studied by means of electronic spekle pattern interferometry (ESPI). The setup allowed the authors to analyze in detail the transitions from elastic to plastic behavior and from homogeneous to inhomogeneous plastic deformation. In agreement with the conventional definition of the yield point for copper fully plastic behavior starded at permanent strains close to 0.005. The strain-hardening coefficient was very low at the early stage of plastic flow (“easy glide”), increasing progressively until values on the order of 0.13 to 0.14 were reached at maximum load. A this point, the appearance of unequally spaced fringes signaled the beginning of inhomogeneous deformation. With ESPI, this occurrence may thus serve as a criterion to establish the forming limit of the material.     

Micro/macromechanical plastic limit analyses of composite materials and structures

The load-bearing capacities of ductile composite materials and structures are studied by means of a combined micro/macromechanics approach. Firstly, on the microscopic scale, the aim is to get the macroscopic strength domains by means of the homogenization theory of micromechanics. A representative volume element (RVE) is selected to reflect the microstructures of the composite materials. By introducing the homogenization theory into the kinematic limit theorem of plastic limit analysis, an optimization format to directly calculate the limit loads of the RVE is obtained. And the macroscopic yield criterion can be determined according to the relation between macroscopic and microscopic fields. Secondly, on the macroscopic scale, by introducing the Hill's yield criterion into the kinematic limit theorem, the limit loads of orthotropic structures such as unidirectional fiber-reinforced composite structures are worked out. The finite element modeling of the kinematic limit analysis is deduced into a nonlinear mathematical programming with equality-constraint conditions that can be solved by means of a direct iterative algorithm. Finally, some examples are illustrated to show the application of the present approach. Project supported by the National Natural Science Foundation of China (No. 19902007), the National Foundation for Excellent Doctoral Dissertation of China (No. 200025), the Fund of the Ministry of Education of China for Returned Oversea Scholars and the Basic Research Foundation of Tsinghua University.     

Three-dimensional stress-relief displacements from blind-hole drilling: a parametric description

Optically-based interferometric techniques are finding increased application to the quantitative determination of near surface stress states. Unlike the standardized strain-gage method of hole drilling, however, some optical methods are sensitive to all three components of the displacement field produced by drilling of the stress-relieving hole. Analysis of the resulting fringe patterns necessitates a full knowledge of such motions. Here, direct formulae, which relate stress-relief displacements to radial position and azimuth, relative hole dimensions, residual or applied stress, and Poisson's ratio, are constructed from an extensive series of finite element calculations. The final formulae are derived from a large set of trial formulae that best describe the displacements according to a statistical regression analysis. The formulae are generally valid for hole depth/diameter ratios from 0.5 to 4.0, for Poisson's ratios from 0.05 to 0.45, and over radial distances from the hole axis from 2 to 20 times the hole radius, although these validity ranges can vary with hole depth. The equations are compared to an existing strain-gage hole-drilling standard and are used to forward model a speckle interferometer fringe pattern recording stress-relief displacements in an acrylic block.     

基于均匀化理论的管板有效弹性常数的研究

根据多尺度均匀化理论建立了管板有效弹性常数研究的有限元计算模型，在弹性平面状态下，计算结果与ASME规范中采用的有效弹性常数进行了比较，其相对误差在0．2％，然后对管板中胀接管子的加强作用进行了研究，得到了管板有效弹性常数与胀接管子在孔间带效率为0．4时的变化曲线。计算结果表明，用均匀化方法计算管板的有效弹性常数是可行的。     

血红细胞力学性能的纳米压痕实验和有限元模拟

采用纳米压痕技术和有限元方法研究了血红细胞的生物力学性能. 进行了血红细胞的纳米压痕实验, 得到了血红细胞的材料参数和变形形貌; 在实验基础上, 建立了血红细胞的三维有限元模型, 模拟了血红细胞的压痕载荷-位移曲线, 并考虑了参数效应. 数值模拟结果和实验数据符合很好. 通过改变压头与材料之间的摩擦系数和压头曲率半径等参数, 比较了载荷-位移曲线的变化情况. 研究表明摩擦系数对压痕载荷-位移曲线和应力分布影响很小, 而压头曲率对载荷-位移曲线的影响明显.     

纳米压痕过程的三维有限元数值试验研究

采用有限元方法模拟了纳米压痕仪的加、卸载过程，三维有限元模型考虑了纳米压痕仪的标准Berkovich压头．介绍了有限元模型的几何参数、边界条件、材料特性与加载方式，讨论了摩擦、滑动机制、试件模型的大小对计算结果的影响，进行了计算结果与标准试样实验结果的比较，证实了模拟的可靠性．在此基础上，重点研究了压头尖端曲率半径对纳米压痕实验数据的影响．对比分析了尖端曲率半径r＝0与r＝100nm两种压头的材料压痕载荷—位移曲线．结果表明，当压头尖端曲率半径r≠0时，基于经典的均匀连续介质力学本构理论、传统的实验手段与数据处理方法，压痕硬度值会随着压痕深度的减小而升高．     

On the Size of RVE in Finite Elasticity of Random Composites

This paper presents a quantitative study of the size of representative volume element (RVE) of random matrix-inclusion composites based on a scale-dependent homogenization method. In particular, mesoscale bounds defined under essential or natural boundary conditions are computed for several nonlinear elastic, planar composites, in which the matrix and inclusions differ not only in their material parameters but also in their strain energy function representations. Various combinations of matrix and inclusion phases described by either neo-Hookean or Ogden function are examined, and these are compared to those of linear elastic types.     

Computer simulation of tensile deformation of aluminium bicrystalline specimen by means of elasto-plastic finite element method of crystal

Based on the experimental data of strain-stress relation of single crystal and the complexity of polycrystal deformation, a calculating model is proposed and the calculating program is designed. Finally, the tensile deformation of the bicrystal aluminium specimen is simulated by means of the crystal elasto-plastic finite element method. The strain-stress curve of tension, the details of the slip deformation and the stress distribution are obtained. So the effect of the region near grain boundary is shown obviously.     

考虑孔隙影响的混凝土有效弹性模量预测分析研究

本文通过纳米压痕实验技术得到混凝土材料细观各相参数，基于渐进均匀化理论，采用蒙特卡洛方法和双向游走方法建立了含孔隙混凝土的胞元模型．分析了孔隙在冻融循环次数增加情况下对混凝土有效弹性模量的影响，同时与有限元模拟分析进行了比较．结果表明：随着冻融循环次数增加，孔隙体积分数增大，界面与砂浆压痕模量相对降低，但对骨料影响较小，导致混凝土宏观弹性模量随之降低；理论分析预测的混凝土有效弹性模量与有限元模拟结果吻合良好．应用含孔隙混凝土胞元模型能有效地预测混凝土宏观弹性模量，进而也为其在冻融作用下老化演变机理的研究评估提供了基础．