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。     

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。     

阳极氧化铝基体上非晶态碳纳米纤维阵列膜的微观组织及其摩擦性能

采用乙炔热分解法在多孔阳极氧化铝膜板上制备了定向生长的非晶态碳纳米纤维阵列膜，采用场发射扫描电子显微镜、激光Raman光谱仪和透射电子显微镜观察分析了阵列膜和非晶态碳纳米纤维的组织形态和微观结构，并采用原子力显微镜和环-块式摩擦磨损试验机考察了非晶态碳纳米纤维阵列膜的摩擦性能．结果表明：以经草酸溶液二次阳极氧化得到的有序多孔氧化铝薄膜作为模板，通过化学催化气相沉积可以获得分布均匀的非晶态碳纳米纤维阵列，这种定向非晶态碳纳米纤维阵列构成的表面膜摩擦力均匀，具有优良的自润滑作用．     

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。     

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。     

某纳米级机械振荡器的非线性自由振动特性分析

主要对某纳米级振荡器的非线性自由振动特性进行了初步的研究。基于Lennard-Jones势能推导了单位面积的平板与无限长平板间的势能。为计算方便，引入无量纲化变量，给出了纳米级振荡器非线性自由振动的状态方程和Hamilton函数。根据负的Lennard-Jones力曲线和弹簧力曲线的相交特性，对非线性自由振动的平衡位置特性进行了分析，指出了影响平衡位置特性的若干重要参量。对给定参量的非线性自由振动的相位图特性、振动周期等进行了定量及定性研究。     

电镀铜薄膜力学性能的实验研究

电子器件中大量使用铜膜作为电信号通道,而且一般采用电镀工艺制成.铜膜的力学性能参数对于其热疲劳可靠性的研究非常重要.目前有关该材料的力学性能研究尚不充分,而且数据极为不统一.本文借助于纳米压痕法、声发射等实验手段对电镀铜薄膜的静态力学性能(包括弹性模量和屈服强度等)及疲劳性能进行了测试.结果发现,与大块铜材料相比,电镀铜薄膜的弹性模量低很多,但屈服强度与大块铜材料相当,甚至高出200％.同时,本文采用弯曲疲劳实验,以电阻变化为失效判据,对镀铜材料的疲劳性能进行了测试,获取了该材料不同失效判据下的疲劳寿命预测模型的系数.     

多孔氧化铝陶瓷储油材料的摩擦学性能研究

用石墨作为造孔剂,利用模压成型高温烧结方法制备了分布均匀的多孔氧化铝陶瓷,将多孔氧化铝陶瓷浸渍甲基硅油得到多孔氧化铝储油材料,在THT07-135型高温摩擦磨损试验机上考察了其同Si3N4陶瓷球对摩时的摩擦磨损性能,用扫描电子显微镜观察分析了磨损表面形貌.结果表明,浸渍甲基硅油后多孔氧化铝陶瓷的减摩抗磨性能显著改善,这是由于储存在多孔氧化铝陶瓷中的润滑剂起到润滑作用并抑制偶件的氧化磨损所致.     

利用纳米硬度试验法确定Cr/Cu梯度材料的变形特性

利用纳米硬度仪研究了在Cu基底上的Cu／Cr梯度膜的机械性能。梯度膜是通过将Cu靶和Cr靶同时溅射到Cu基底材料上，但两个靶的相对溅射功率随溅射时间变化而制备。利用Oliver and Pharr方法得到了膜随其厚度变化的硬度和弹性模量。然后利用加载／卸载／再加载的方法得到了在不同深度(即膜的厚度)压头平均压力与相对压人深度之间的关系曲线，在此曲线上可以明显反映出材料的屈服特性。     

Determining the Elastic Modulus of Compliant Thin Films Supported on Substrates from Flat Punch Indentation Measurements

Instrumented indentation is a technique that can be used to measure the elastic properties of soft thin films supported on stiffer substrates, including polymer films, cellulosic sheets, and thin layers of biological materials. When measuring thin film properties using indentation, the effect of the substrate must be considered. Most existing models for determining the properties of thin films from indentation measurements were developed for metal and dielectric films bonded to semiconductor substrates and have been applied to systems with film-substrate modulus ratios between 0.1 and 10. In the present work, flat punch indentation of a thin film either bonded to or in contact with a substrate is examined using finite element modeling. A broad range of film-substrate modulus ratios from 0.0001 to 1 are investigated. As the substrate is effectively rigid compared to the film when the film-substrate modulus ratio is less than 0.0001, the results are also useful for understanding systems with lower film-substrate modulus ratios. The effects of the contact radius, film thickness, elastic properties, and friction between the film and the substrate on the measured stiffness were quantified using finite element modeling in order to understand how the elastic properties of the film can be extracted from indentation measurements. A semi-analytical model was developed to describe the finite element modeling results and facilitate the use of the results to analyze experimental measurements. The model was validated through analysis of indentation measurements of thin polyethylene sheets that were supported on substrates of various stiffness.     

Elastic modulus measurements of vertically aligned multi walled carbon nanotubes carpets by using the nanoindentation technique

Electrical, thermal and mechanical properties of Vertically Aligned Multi Walled Carbon NanoTubes (VA-MWCNT) make them an ideal candidate to replace some of conventional materials in micro and nano-electronic components. Integrating this material in micro components requires a good knowledge of their properties. As the electrical and thermal properties, the MWCNT mechanical properties are difficult to assess. Several techniques have been developed to estimate the CNT Young's modulus and the obtained results cover a large range of scale. In this study, we propose an indirect technique for MWCNT carpet Young's modulus measurements by using the nanoindentation technique. Nanoindentation tests are performed on a metallic film deposited on MWCNT. The measured equivalent reduced modulus takes into account the elastic properties of the metallic thin film and those of the MWCNT substrate. Bec et al. model, introduced in 2006, is used to separate elastic properties, and thus determine the MWCNT reduced Young’s modulus which is estimated between 329 and 352 GPa. Knowing the indenter mechanical properties, we estimate the Young’s modulus in the 461 to507 GPa range.     

Analysis of elastic and plastic deformation associated with indentation testing of thin films on substrates

A study has been made of the elastic and plastic deformation associated with submicrometer indentation of thin films on substrates using the finite element method. The effects of the elastic and plastic properties of both the film and substrate on the hardness of the film/substrate composite are studied by determining the average pressure under the indenter as a function of the indentation depth. Calculations have been made for film/substrate combinations for which the substrate is either harder or softer than the film and for combinations for which the substrate is either stiffer or more compliant than the film. It is found, as expected, that the hardness increases with indentation depth when either the yield strength or the elastic modulus of the substrate is higher than that of the film. Correspondingly, the hardness decreases with indentation depth when the yield strength or elastic modulus of the substrate is lower than that of the film. Functional equations have been developed to predict the hardness variation with depth under these different conditions. Finite element simulation of the unloading portion of the load displacement curve permits a determination of the elastic compliance of the film/substrate composite as a function of indentation depth. The elastic properties of the film can be separated from those of the substrate using this information. The results are in good agreement with King's analytical treatment of this problem.     

Resonant and Stationary Waves in Rotating Disks

The analytical conditions for resonant and stationary waves inrotating disks are presented. These conditions are derived from anonlinear plate theory pertaining to initial configurations and areapplicable to rotating disks with initial waviness and/or undergoinglarge-amplitude displacements. The rotational speeds at which theresonant and stationary waves occur for a 3.5-inch diameter computermemory disk are computed. The resonant waves for linear and nonlinear,rotating disks are simulated numerically. It is found that some diskmodes exhibit a hardening effect under which the rotational speeds forthe resonant and stationary waves increase with increasing waveamplitude, while other modes experience a softening effect with thoserotational speeds decreasing with increasing wave amplitude. Therotating-disk resonant spectrum presented in this paper is relevant tothe disk drive industry for determining the range of operationalrotation speed.     

The stiffness and strength of the gyroid lattice

Recently, a nanoscale lattice material, based upon the gyroid topology has been self-assembled by phase separation techniques (Scherer et al., 2012) and prototyped in thin film applications. The mechanical properties of the gyroid are reported here. It is a cubic lattice, with a connectivity of three struts per joint, and is bending-dominated in its elasto-plastic response to all loading states except for hydrostatic: under a hydrostatic stress it exhibits stretching-dominated behaviour. The three independent elastic constants of the lattice are determined through a unit cell analysis using the finite element method; it is found that the elastic and shear modulus scale quadratically with the relative density of the lattice, whereas the bulk modulus scales linearly. The plastic collapse response of a rigid, ideally plastic gyroid lattice is explored using the upper bound method, and is validated by finite element calculations for an elastic-ideally plastic lattice. The effect of geometrical imperfections, in the form of random perturbations to the joint positions, is investigated for both stiffness and strength. It is demonstrated that the hydrostatic modulus and strength are imperfection sensitive, in contrast to the deviatoric response. The macroscopic yield surface of the imperfect lattice is adequately described by a modified version of Hill’s anisotropic yield criterion. The article ends with a case study on the stress induced within a gyroid thin film, when the film and its substrate are subjected to a thermal expansion mismatch.     

Indentation tests investigation of mechanical behavior of two-dimensional materials

准确了解二维材料的力学性能对于推动其应用具有重要意义, 无基底压痕技术是目前最广泛采用的二维材料力学性能测试方法之一, 本文综述了二维材料压痕研究的最新进展以及所面临的问题, 并对将来的研究工作进行了展望.无基底压痕技术是将二维材料转移到带有沟槽或柱形孔的基底上, 制备二维材料"梁"和"鼓"模型, 然后利用原子力显微镜测量其在压针作用下的载荷--位移关系, 最后通过基于连续介质薄膜导出的压痕响应分析模型拟合实验结果, 估算出二维材料的弹性模量和本征强度.由于二维材料的厚度远小于连续介质薄膜, 来自于压头以及基底孔侧壁的范德华力对二维材料的压痕响应具有显著影响, 造成二维材料与传统压痕分析模型中的基本假设不符, 导致不能准确预测二维材料的弹性模量; 另外, 由于传统压痕模型无法准确描述二维材料在大变形下的非线性行为, 以及由缺陷等引起的应力集中, 导致由压痕测试表征的二维材料(特别是多晶二维材料)本征强度具有较大的偏差. 因此, 一方面需要正确了解由压痕技术获得的二维材料力学性能, 另一方面还需对目前的研究方法做进一步的改进和完善.     

二维材料力学行为的压痕测试

准确了解二维材料的力学性能对于推动其应用具有重要意义, 无基底压痕技术是目前最广泛采用的二维材料力学性能测试方法之一, 本文综述了二维材料压痕研究的最新进展以及所面临的问题, 并对将来的研究工作进行了展望.无基底压痕技术是将二维材料转移到带有沟槽或柱形孔的基底上, 制备二维材料"梁"和"鼓"模型, 然后利用原子力显微镜测量其在压针作用下的载荷--位移关系, 最后通过基于连续介质薄膜导出的压痕响应分析模型拟合实验结果, 估算出二维材料的弹性模量和本征强度.由于二维材料的厚度远小于连续介质薄膜, 来自于压头以及基底孔侧壁的范德华力对二维材料的压痕响应具有显著影响, 造成二维材料与传统压痕分析模型中的基本假设不符, 导致不能准确预测二维材料的弹性模量; 另外, 由于传统压痕模型无法准确描述二维材料在大变形下的非线性行为, 以及由缺陷等引起的应力集中, 导致由压痕测试表征的二维材料(特别是多晶二维材料)本征强度具有较大的偏差. 因此, 一方面需要正确了解由压痕技术获得的二维材料力学性能, 另一方面还需对目前的研究方法做进一步的改进和完善.      

On the determination of the Young’s modulus of thin films using indentation tests

The main difficulty with the characterization of thin coatings using depth-sensing indentation tests is related to the determination of the contributions of the substrate and the film to the measured properties. In this study, three-dimensional numerical simulations of the Vickers hardness test are used in order to examine the influence of the elastic and plastic properties of the substrate and the film on the composite’s Young’s modulus results. The hardness of the film is equal to or higher than the substrate hardness. A study of the stress distributions and the indentation geometry of composites, film/substrate, was performed, taking into account the relative mechanical properties of the film and substrate. In addition, stress evolution during indentation was studied, in order to quantify the critical indentation depth under which the substrate is not elastically deformed. The accurate evaluation of the Young’s modulus of the films using weight functions is also examined: some of these have previously been proposed and one was introduced for this study. Two different fitting procedures were used to compare the results obtained from eight fictive film/substrate combinations using six weight functions. The first procedure, commonly used, considers the substrate’s modulus as a known parameter in the fitting process. In the second, the film and the substrate’s modulus are considered as unknown variables that are calculated simultaneously during the fitting process. The validity of the conclusions obtained using the fictive materials was checked by applying the weight functions to four real composites.