Microelectromechanical Systems for Nanomechanical Testing: Displacement- and Force-Controlled Tensile Testing with Feedback Control

Experimental Mechanics - Background: MEMS-based nanomechanical testing has received much interests. However, it remains challenging to perform displacement- and force-controlled nanomechanical...     

微机械加速度计及电容检测电路的设计

本文讨论一种扭摆式微机械加速度计.介绍其敏感元件的结构,振动模态和数学模型,说明了集成电容检测电路的原理,并对该电路进行了具体设计,利用PSPICE软件进行仿真分析,结果证明完全达到要求,并给出了同步解调器电路的形式,为进行版图设计打下了基础.     

基因芯片纳米挠度和表面应力的解析预测

本文利用能量法解析分析了无标记生物检测中基因芯片的纳米力学行为.首先,考虑微悬臂梁机械能和基因层静电能、水合能和构型熵,建立了基因芯片能量模型,并采用泰勒级数展开法.获得了能量势的一阶近似式.其次,利用能量最小原理,得到了芯片稳态弯曲的曲率半径、纳米挠度和表面应力的解析表达式,从而克服了求解多极值能量泛函数值解的困难.最后,预测了DNA的链长和种植密度对芯片纳米力学行为的影响,同时将表面应力的解析预测结果与有关实验数据进行了比较,证明了本文方法的可靠性.     

Nanomechanical Property and Nanowear Measurements for Sub-10-nm Thick Films in Magnetic Storage

In the magnetic storage industry, thin film carbon overcoats play a critical role in reducing magnetic and physical spacing between the recording slider and the rotating disk so that the information stored per unit area is maximized. Thin film carbon overcoats have been improved such that they exhibit higher hardness with lower thickness of few nanometers and still being able to perform reliably. In this paper, nanoindentation and nanoscratch techniques to measure nanomechanical properties, namely hardness, elastic modulus and shear strength of thin solid films were presented along with a recently developed high resolution force transducer. Nanowear behavior characterization techniques were also examined and were applied to commercially available magnetic disks to characterize their wear behavior. It was shown that the properties and wear behavior of sub-10-nm thick film carbon overcoats were reliably measured. These techniques could be applied to different thin solid films on substrates, and they are not restricted to magnetic storage systems.     

Microfluidics for Porous Systems: Fabrication,Microscopy and Applications

Transport in Porous Media - No matter how sophisticated the structures are and on what length scale the pore sizes are, fluid displacement in porous media can be visualized, captured, mimicked and...     

螺桨盘转子轴头动刚度实验测量方法及技术处理

在螺桨盘转子系统的颤振涡动研究中,系统的安装刚度对转子的颤振涡动失稳有着重要的作用.对于飞机发动机,实际安装情况十分复杂,发动机短舱.安装节、机翼等对螺桨盘转子的运动均有影响.所以,在颤振涡动研究中,必须考虑轴头的动刚度.轴头的动刚度是通过动柔度转换而来的,而在动柔度的实验测量中必须解决几个技术问题,首先是提高信噪比.其次是消除工艺夹具带来的附加质量和附加转动惯量的影响,从而提高动刚度系数的测量精度.本文通过对模型转子以及某实际桨轴发动机转子轴头动刚度系数的测量及处理,阐述轴头动刚度矩阵的测量方法,以及有关技术问题的处理过程.     

安全绳坠落试验及分析

对多种不同型号的安全绳、缓冲包及假人系统开展实验室坠落试验分析．研究发现,相邻二次冲击的冲量之比,及相邻二次冲击的自由抛体运动持续时间之比都近似为一个定值,利用该统计规律导出估算阻尼系数的近似方法,并利用首次冲击波形的试验结果得到了三次幂非线性刚度系数,相关结果可作为安全绳性能评估的重要依据．     

Actuation of the Kagome Double-Layer Grid. Part 2: Effect of imperfections on the measured and predicted actuation stiffness

The actuation stiffness of a set of steel Kagome Double-Layer Grid (KDLG) structures with brazed joints is measured experimentally and compared with predictions by the finite element method. The predicted actuation stiffnesses for the perfect KDLGs much exceed the measured values, and it is argued that the low values of observed actuation stiffness are due to the presence of geometric imperfections introduced during manufacture. In order to assess the significance of geometric defects upon actuation stiffness, finite element calculations are performed on structures with a stochastic dispersion in nodal position from the perfectly periodic arrangement, and on structures with wavy bars. It is found that bar waviness has the dominant effect upon the actuation stiffness. The predicted actuation stiffness for the imperfect structures are in satisfactory agreement with the measured values assuming the same level of imperfection between theory and experiment.     

机械性能测试中图形的在线截取和重显

本文针对国产ＷＡＷ－１００万能试验机所带测试软件的不足，给出了采用ＴＳＲ技术对万能试验机在不同的试验情况下产生的变形曲线进行截取、储存，然后将截取的曲线在同一坐标系下进行重显的方法和程序，从而实现了对各种试验所测数据和曲线进行跟踪、比较和分析．     

新型小载荷冲击磨损试验机的研制及其实验研究

设计并研制出新型小载荷冲击磨损试验机,介绍了该试验机的工作原理、结构及其主要技术参数,并采用所研制的试验机对TC4钛合金进行了8个不同周次的3组冲击磨损试验.结果表明:TC4钛合金的冲击坑形貌规整,具有明显的表面特征和累计损伤特征;在相同试验条件下试验结果的重现性较好,数据最大误差小于6%;试验机所加载荷稳定,长时运行无过流过温现象,能够满足小载荷冲击磨损试验的要求.     

Vehicle-wet snow interaction: Testing,modeling and validation

For a vehicle interacting with snow, whether dry or wet, uncertainties exist in the mechanical properties of snow, and in the interfacial properties between the tires of the vehicle and snow. For dry snow, these uncertainties have been studied recently using methods within a statistical framework employing a simple stochastic tire-snow interaction model and several validation metrics. Wet snow is more complicated and much less studied than dry snow, especially for tire-snow interaction. In this paper, the authors used a physical tire-snow interaction model and a similar statistical framework as was used to analyze dry snow, and presented results of calibration and validation of the interaction model for wet snow in conjunction with new test data based on a single test run with the assumption that it would provide needed sampling points for statistical analysis. Four local and global statistical validation metrics were used to assess the physical and statistical models with good results. Comparison between wet and dry snow, based on a single test run, shows that the former has a lower interfacial coefficient of friction, and a higher drawbar pull than the latter.     

多轴承动载下摆动疲劳试验方法

本文就多轴承动载下摆动疲劳试验方法进行了研究,对试验夹具和试验中发现的问题进行了探讨和分析。在试验完成后,对试验轴承进行了分解检查,并在此基础上对试验方法和夹具提出了新的设想和改进措施。     

Algorithms for Nanoindentation Strain Rate Jump Testing and Analysis

Experimental Mechanics - Understanding the dynamics of deformation processes is of interest for determining the dominant thermally activated processes during plasticity [1] and fracture [2, 3]....     

Birkhoff系统的积分因子与守恒定理

本文提出了构造Birkhoff系统守恒律的积分因子方法。首先，给出了Birkhoff方程的积分因子的定义，研究了Birkhoff系统的守恒量存在必要条件；其次，建立了系统的积分因子与守恒律的对应关系，并给出了用于确定积分因子的广义Killing方程，最后，建立了守恒定理的逆定理。文末，举例说明结果的应用。     

Out-of-plane Testing Procedure for Inverse Identification Purpose: Application in Sheet Metal Plasticity

Many recent works in inverse identification of constitutive parameters have pointed to the need of tests which exhibit heterogeneous strain paths. The present study details a new testing procedure based on out-of-plane motion capture by Stereo-Image Correlation (SIC). With the original test proposed hereby, a unique sample is deformed on a tensile machine along two perpendicular tensile directions, two perpendicular shear directions and one expansion area. The choice of the sample shape is discussed along with the stereo imaging device, 3D reconstruction and measurement uncertainties. The test sample is made from a sheet of commercially pure titanium. A Finite-Element updating inverse method is applied in order to identify six parameters of an anisotropic plastic constitutive model. Results show that this new testing procedure allows every constitutive parameter of the model to be identified from one and only one test.     

Stress- and Temperature-Dependent Wideband Fluorescence of a Phosphor Composite for Sensing Applications

As both stress and temperature can alter the lattice of a solid phosphor in a similar way, the dopant rare-earth ion may be used as a probe for either parameter using the same sensing mechanism. Here, a wideband phosphor, YAG:Ce is used as a micro stress sensor at very low magnitudes of compressive stress. The sensing resolution can be smaller than 0.06 N/mm² in the range of 0?~?1.2 N/mm² with a sensitivity of 11 cm^?1/MPa. The sensitivity is about a hundred times larger than the coefficient reported under hydrostatic pressure. The barycenter energy of the emission band of a phosphor can be used to indicate stress and/or temperature change, producing a precision beyond the spectroscopic resolution limit. The sensing functions obtained from the barycenter shift are superior to those from peak shifts. The stress/temperature dependent barycenter shift of the observed fluorescence bands of YAG:Ce were similar in magnitude. Mechanisms involving the nephelauxetic effect, crystal field effect and site symmetry of dopant ions are explored as explanations of the experimental phenomena.