基于Total—Lagrange法SMA算法接头的有限元分析

基于非线性连续介质力学的有限变形理论和Ｔｏｔａｌ－Ｌａｇｒａｎｇｅ增量方法，考虑到形状记忆合金材料（ＳＭＡ）的强物理非线性，推导了适用于有限元计算的虚功方程和增量型本构方程，并相应编制了考虑物理非线性有限变形的增量有限元程序，特别讨论了计算中应注意的问题和处理方法。最后采用该方法模拟ＳＭＡ管接头的工作过程，研究了影响接触应力、扩孔载荷、加热温度等的几个因素。     

形状记忆合金超弹性缆索力学行为的有限单元法

由于涉及材料和接触双重非线性问题,很难建立描述形状记忆合金(Shape memory alloy,SMA)超弹性缆索力学行为的理论模型,为了克服试验成本高和易受环境因素影响的缺点,基于形状记忆因子概念和SMA本构模型,推导了适于有限单元法的增量型SMA本构模型。利用ABAQUS二次开发功能,考虑相变过程中SMA弹性模量的变化,编写了SMA用户材料子程序,实现了SMA超弹性缆索力学行为的有限元单元法。利用建立的有限单元法对SMA超弹性缆索的相变和力学行为进行数值模拟,并将数值结果与文献中试验结果进行了对比验证,在此基础上,分析了SMA超弹性缆索外线股螺距对缆索整体力学行为的影响。计算结果及其与试验结果的对比表明,提出的有限单元法能有效描述和预测SMA超弹性缆索在拉伸过程中的相变和力学行为,SMA超弹性缆索外线股轴线螺距对缆索整体相变和力学行为有明显影响,研究工作可为SMA超弹性缆索设计及工程应用提供计算方法与技术指导。     

无网格法在几何非线性力学中的应用

利用无网格法分析几何非线性力学问题,建立拉格朗日坐标系下基于移动最小二乘法的无网格静力学和动力学模型,并采用载荷增量和修正牛顿迭代法相结合的混合法对静力学模型进行方程求解,采用Wilson-θ法求解动力学模型方程.最后计算直杆和悬臂梁在载荷作用下的变形结果与动力响应,并将计算结果与有限元方法的相比较,结果表明,本文方法是可行的.     

计及非线性变形的空间自由旋转梁有限元模型

根据柔性梁的几何非线性变形理论,针对大范围运动的空间柔性梁,在考虑了弯曲和扭转的非线性因素对3个变形方向的影响的基础上,利用有限元方法进行离散,得到了较为精确的变形模式。利用Lagrange方程建立了非线性变形模式下的动力学方程,该方程包含了较为完全的刚度矩阵和各种耦合项。对一带有扭转弹簧的中心体-空间柔性梁结构进行仿真计算,说明变形耦合在横向变形中的作用不可忽视。     

水工钢结构焊接残余应力有限元模拟分析

采用有限元数值计算方法模拟了钢结构在焊接过程中产生的残余应力和变形特性,采用了双线性弹性-塑性模型、Von Mises屈服准则,和增量原理处理焊接过程中的材料非线性问题,建立了热-结构耦合有限元模型和方法。数值仿真结果表明,采用单元生死处理方法对于模拟多道焊缝问题是有效的。     

基于二次摄动法的SMA层合梁非线性自由振动分析

为对SMA(形状记忆合金)层合梁的非线性自由振动进行分析,使用Brison一维本构模型描述SMA的力学特性,基于不同剪切函数和Von Karman大变形理论,建立梁质点位移与应变之间的关系,使用Hamilton变分原理,获得在弹性地基上两端简支SMA层合梁的动力学方程并进行无量纲处理。使用二次摄动法获得SMA层合梁的非线性自由振动方程。研究不同SMA体积分数、预应变、SMA铺设角度、温度变化对非线性振动的影响。     

形状记忆合金梁的非线性弯曲变形

形状记忆合金(Shape memory alloy,SMA)梁作为一种新型智能元件,在工程领域的应用日益广泛。基于实测的形状记忆合金材料应力-应变关系曲线及梁的大变形理论,同时考虑SMA材料拉压力学性能的不对称性及简支端移动等因素,建立形状记忆合金梁非线性弯曲变形的控制方程,并采用打靶法、辛普森数值积分等方法对方程进行数值求解。通过梁在不同载荷条件下的挠曲线以及最大挠度—弯矩曲线,分析材料非线性、几何非线性及简支端移动3个因素对SMA超弹性梁弯曲变形的影响规律。结果表明:梁中性层位置随弯矩变化;弯矩较小时,材料性能是线性的,几何非线性及简支端移动对梁的弯曲变形几乎不产生影响;弯矩较大时,材料性能是非线性的,几何非线性及简支端移动对梁的弯曲变形产生明显影响。     

圆柱壳结构外压弹塑性稳定性问题的半解析有限元法

综合考虑几何、物理双重非线性因素的影响,对圆柱壳结构在外压作用下发生承受外压失稳屈曲进行研究.几何方程采用大位移的应变位移关系,物理方程采用弹塑性分析的应力应变关系,导出圆柱壳单元弹塑性分析的切线刚度矩阵.计算中,为追踪失稳屈曲完整的平衡路径,在位于极值点邻域内的每一增量步中,采用控制弧长约束下的增量-迭代法进行计算,使计算效率大大提高.     

多支承“主轴—轴承”系统变形的非线性边界有限元分析

在计算主轴部件的静载变形时，往往需要综合考虑主轴本身以及轴承的变形。在有限元计算的边界条件可以很方便地计入轴承的变形，但这仅限于轴承的“载荷－变形”曲线是线性的情况。实际上多数轴承的“载荷－变形”曲线是非线性的，这使有限元具有非线性的边界条件。本文着重讨论了这种非线性边界条件下的有限元方程的建立及其求解方法。 [1]单元划分 　　对主轴静载变形作有限元分析时，可在轴线方向将主轴划分成离散的一维梁单元。划分单元时，将不同直径的轴段 (包括退刀槽和越程槽 )划分为不同的单元，主轴上受集中载荷的点以及轴承的安…     

柔性梁式构件的多体系统动力学方法研究

采用有限段方法建立柔性梁式构件的离散模型，以基于Ｋａｎｅ方程的Ｈｕｓｔｏｎ方法建立柔性梁式构件的多体系统动力学方程，在方程中，计入梁式构件的几何非线性变形的惯性影响，包括了非对称截面当量弹性力对广义动力的贡献。在求解过程中，引入了相对位移的模态变换以提高计算效率，通过典型算例验证此方法可以用于具有几何非线性变形的柔性梁式构件的多体系统。     

二烷基二硫代磷酸钕作为锂基脂添加剂的极压抗磨作用机理

合成了二正十六烷基二硫代磷酸阴离子与稀土离子（Ｎｄ＾３＋）的中性络合物，考察了具有类似配体结构的稀土和过渡金属（Ｚｎ）络合物对锂基脂摩擦学性能的影响，通过Ｘ光光电子能谱对添加剂的作用机理进行了研究。     

用普通水玻璃砂铸造高精度齿条工艺方案的优化

齿条的齿部尺寸精度和表面平整度要求较高,采用普通水玻璃砂手工生产方式铸造难度很大,试制过程往往解决了一些问题又出现一些新的问题,在不断的实践摸索中,我们终于找到最优工艺方案。采用该方案生产出2640件齿条,全部符合质量要求。     

An assessment of the homogeneity of nano-crystalline Fe–Cu powders as studied by means of APT

In this contribution the homogeneity of mechanically alloyed Fe–Cu powders for two different compositions (Fe-10 and Fe-2.5 at%Cu) has been systematically characterised by atom probe tomography. Since Fe–Cu exhibits the Invar effect, it is among the most attractive systems for technical application. Furthermore, this system is immiscible and characterised by a large positive heat of mixing. In combination with the widespread application and accessibility, this predestines Fe–Cu as a binary model alloy to elaborate the enforced nonequilibrium enhanced solubility for immiscible systems. Depending on the parameters composition and milling time, results on the extension of the solubility limit and on the homogeneity of the alloy are presented, discussed and compared to earlier works. Only for the alloy with lower Cu content and for the prolonged milling time of 50 h, chemical homogeneity of the sample as measured by the atom probe was fully reached on the nano-scale. For all other parameter combinations homogeneity could not be achieved, even for long milling times and for those samples that appear to be homogeneous via X-ray analysis. Moreover, impurities were determined, mostly stemming from the fabrication procedure. The arrangement and homogeneity of the most common impurity, oxygen, was evaluated from atom probe data for different samples.     

Effect of SP-C on surface potential distribution in pulmonary surfactant: Atomic force microscopy and Kelvin probe force microscopy study

The air–lung interface is covered by a molecular film of pulmonary surfactant (PS). The major function of the film is to reduce the surface tension of the lung's air–liquid interface, providing stability to the alveolar structure and reducing the work of breathing. Earlier we have shown that function of bovine lipid extract surfactant (BLES) is related to the specific molecular architecture of surfactant films. Defined molecular arrangement of the lipids and proteins of the surfactant film also give rise to a local highly variable electrical surface potential of the interface. In this work we investigated a simple model of artificial lung surfactant consisting of DPPC, eggPG, and surfactant protein C (SP-C).     

Limits to the spatial, energy and momentum resolution of electron energy-loss spectroscopy

We discuss various factors that determine the performance of electron energy-loss spectroscopy (EELS) and energy-filtered (EFTEM) imaging in a transmission electron microscope. Some of these factors are instrumental and have undergone substantial improvement in recent years, including the development of electron monochromators and aberration correctors. Others, such as radiation damage, delocalization of inelastic scattering and beam broadening in the specimen, derive from basic physics and are likely to remain as limitations. To aid the experimentalist, analytical expressions are given for beam broadening, delocalization length, energy broadening due to core-hole and excited-electron lifetimes, and for the momentum resolution in angle-resolved EELS.     

Near-field visualization of dynamical processes of semiconductor surface

The near-field images calculation method for semiconductor surface with inhomogeneous electron distribution, formed by strong focused laser pulse, was proposed. Calculation is performed using Green function method. The main characteristic of the proposed approach is maximal usage analytical computations. The near-field images for the surface of GaAs were obtained at different points of time. Developed approach is universal and could be able to find with experimental data on time-resolved near-field microscopy some parameters of semiconductor surface such as diffusion constant and relaxation time.     

In situ measurements and transmission electron microscopy of carbon nanotube field-effect transistors

We present the design and operation of a transmission electron microscopy (TEM)-compatible carbon nanotube (CNT) field-effect transistor (FET). The device is configured with microfabricated slits, which allows direct observation of CNTs in a FET using TEM and measurement of electrical transport while inside the TEM. As demonstrations of the device architecture, two examples are presented. The first example is an in situ electrical transport measurement of a bundle of carbon nanotubes. The second example is a study of electron beam radiation effect on CNT bundles using a 200 keV electron beam. In situ electrical transport measurement during the beam irradiation shows a signature of wall- or tube-breakdown. Stepwise current drops were observed when a high intensity electron beam was used to cut individual CNT bundles in a device with multiple bundles.     

A method for fabricating protein patterns on the octadecyltrichlorosialne(OTS) surface through paper swabbing

A simple protein patterning procedure was developed for fabricating clean protein patterns ranging from nanometer to sub-millimeter scale. A carboxylic acid-terminated chemical pattern was fabricated first through the local probe oxidation on the octadecyltrichlorosilane (OTS) film under 100% relative humidity at the first. After incubating the chemical pattern in a protein solution, the sample was swabbed with a piece of ChemWipe paper to selectively remove the non-specifically adsorbed protein. After the swabbing, only the specifically immobilized protein remained on the surface, forming a protein pattern on the chemical template with a very clean background. In our approach, an anti-fouling surface or vigorous rinsing is not required, which simplifies the protein patterning process. As a demonstration of the capability of this protein patterning approach, we fabricated the lysozyme and catalase patterns on the OTS surface. Both patterns were clean and bioactive.     

Direct electron imaging in electron microscopy with monolithic active pixel sensors

A new imaging device for dynamic electron microscopy is in great demand. The detector should provide the experimenter with images having sufficient spatial resolution at high speed. Immunity to radiation damage, accumulated during exposures, is critical. Photographic film, a traditional medium, is not adequate for studies that require large volumes of data or rapid recording and charge coupled device (CCD) cameras have limited resolution, due to phosphor screen coupling. CCD chips are not suitable for direct recording due to their extreme sensitivity to radiation damage. This paper discusses characterization of monolithic active pixel sensors (MAPS) in a scanning electron microscope (SEM) as well as in a transmission electron microscope (TEM). The tested devices were two versions of the MIMOSA V (MV) chip. This 1M pixel device features pixel size of 17 x 17 microm(2) and was designed in a 0.6 microm CMOS process. The active layer for detection is a thin (less than 20 microm) epitaxial layer, limiting the broadening of the electron beam. The first version of the detector was a standard imager with electronics, passivation and interconnection layers on top of the active region; the second one was bottom-thinned, reaching the epitaxial layer from the bottom. The electron energies used range from a few keV to 30 keV for SEM and from 40 to 400 keV for TEM. Deterioration of the image resolution due to backscattering was quantified for different energies and both detector versions.     

JW型激光测微仪在动态测量应用中的研究

本文介绍了JW系列新型激光测微仪的结构、原理、特点,还介绍了利用该仪器在音箱质量检测、记忆合金伸缩特性等科研中对微振动及动态位移进行非接触测量的研究情况,并对测量结果进行了分析.