Extension of the Coherent Gradient Sensor (CGS) to the Combined Measurement of In-Plane and Out-of-Plane Displacement Field Gradients

The Coherent Gradient Sensor (CGS) is extended to the optical differentiation of specular, diffracted wave fronts leading to the combined measurement of in- and out-of-plane displacement field gradients. A derivation of the underlying optical interference principles is presented along with an analysis of the effective instrument sensitivity. In order to demonstrate the capabilities of the technique, experimental measurements of crack-tip deformation fields were conducted under various loading conditions corresponding to mode-I, mode-II, and mixed mode near-tip crack fields. The experimental procedures and results of these tests are presented as validation of the technique.     

On the Use of NURBS Functions for Displacement Derivatives Measurement by Digital Image Correlation

In this paper, we propose to investigate the potential improvement of using Non-Uniform Rational B-Spline (NURBS) functions for displacement measurements by digital image correlation (DIC). The aim is at improving the performance of DIC to capture with low uncertainty and low noise levels not only the displacement field but also its derivatives. Indeed, when the displacement field is used to feed constitutive law identification procedures, displacement derivatives are required and thus may be measured with robustness. Two examples illustrate the potential of NURBS for DIC: a compressive test on a wood sample and a bending test on a steel beam. For the latter, beam kinematics are adopted and NURBS are used in order to capture the variation of the curvature (second derivative of the displacement) along the beam axis. For these two examples, an error study based on a decomposition of the error into the correlation error and the interpolation error, is carried out and shows the great potential of NURBS functions for DIC.     

光学透视测量玻璃纤维增强复合材料板离面应变场分布

本文通过激光波数扫描干涉测量系统和方法,透视测量商用玻璃纤维增强复合材料板前、后表面的离面应变场分布。实验中分别对有缺陷和无缺陷的商用玻璃纤维增强复合材料样品进行了离面位移场测量和平均轴向正应变场分布计算。无缺陷样品的离面位移场及压缩应变场分布均匀连续,随加载呈现递增压缩变化;有缺陷样品的缺陷周围的离面位移场分布变化无规则,其压缩正应变分布以缺陷孔洞为中心,加载量越大,孔洞周围其压缩正应变值较小的区域越大,压缩正应变集中在远离孔洞的边缘区域,随加载量变化压缩应变场分布无线性规律。实验结果证明,激光波数扫描干涉测量系统和方法准确可靠,它为玻璃纤维增强复合材料板的力学性能测量提供了一个新技术平台。     

On Displacement Analysis of the RSSR-SS Mechanism

Abstract

This article presents a method for performing (RSSR-SS) mechanism displacement analysis. The benefit of this method is that it provides a practical alternative for performing RSSR-SS mechanism displacement analysis and is fully applicable with today's mathematics software. This method is an extension of the adjustable RSSR-SS synthesis method developed by the authors (Suh, C. H., Radcliffe, C. W. (1978 Suh, C. H. and Radcliffe, C. W. 1978. “Kinematic analysis of spatial mechanisms”. In Kinematics and Mechanism Design pp. 179–183. New York: John Wiley and Sons.  [Google Scholar]). Kinematic analysis of spatial mechanisms. In: Kinematics and Mechanism Design. New York: John Wiley and Sons, pp. 179–183). By utilizing the passive degree of freedom of the coupler of the RSSR mechanism and its design equations (Sandor, G. N., Erdman, A. G. (1984 Sandor, G. N. and Erdman, A. G. 1984. “Spatial mechanisms with an introduction to robotics”. In Advanced Mechanism Design Analysis and Synthesis pp. 635–641. Englewood Cliffs: Prentice-Hall.  [Google Scholar]). Spatial mechanisms with an introduction to robotics. In: Advanced Mechanism Design Analysis and Synthesis. Englewood Cliffs: Prentice-Hall, pp. 635–641), the design equation for the remaining (S-S) link of the RSSR-SS mechanism was developed using spatial transformation matrices under the constant length condition of the remaining S-S link. The angular rotation about the coupler of the RSSR mechanism, satisfying the constant length equation of this remaining S-S link, was calculated, numerically (Allen M. B. III, Isaacson, E. L. (1998 Allen, M. B. III and Isaacson, E. L. 1998. “Solution of non-linear equations”. In Numerical Analysis for Applied Science pp. 177–187. New York: John Wiley and Sons.  [Google Scholar]). Solution of non-linear equations. In: Numerical Analysis for Applied Science. New York: John Wiley and Sons, pp. 177–187). As an example, the displacement of a series of rigid body points on the coupler of an adjustable RSSR-SS mechanism was calculated for a range of prescribed crank angles.     

微尺度位移、形貌测量系统及应用

研制了一套可应用于MEMS器件的微尺度测量系统，可以在受载状态下实时检测MEMS器件的面内位移、离面位移和三维形貌。该系统中，面内位移测量是一个基于白光数字散斑相关方法的显微光学测量系统，与相应的力学加载系统结合，可以得到MEMS器件在受载状态下的实时面内位移；离面位移和三维形貌测量则是一个基于相移显微投影光栅方法的光学测量系统，与相应的力学加载系统结合，可以得到MEMS器件在受载状态下的实时三维形貌和离面位移。最后给出了几个典型的MEMS器件面内位移、离面位移和三维形貌的实测结果。     

应用云纹干涉法测量冷挤压孔周残余应力分布

本文就冷挤压加工后紧固孔周的残余应力测量问题进行了研究。文中提出了径向切割法以释放欲求剖面的周向残余应力;采用高灵敏度的云纹干涉法测量残余应力释放后引起的附加变形;用载波错位法获得高反差的应变条纹图。     

激光多光束闸墩位移测量研究

根据实际大型工建筑测试的需要，研究激光多光束的全变位测试方法，提出了相应的计算公式，研究了制造了实用的测试装置，并对大型闸墩进行了实地测量，分析了闸体的损伤程度，作了安全评估。     

Nano-Pattern Recognition and Correlation Technique for Sub-Nanometer In-Plane Displacement Measurement

An experimental technique to measure sub-nanometer scale in-plane deformations on a micron scale region of interest is proposed. The proposed Nano-Pattern Recognition and Correlation Technique (N-PRCT) utilizes regularly oriented patterns. Displacements are obtained by tracking the movement of each pattern on the images before and after loading through pattern recognition and correlation. The regularity offers a special benefit, relative to the random markings used in the existing techniques, which makes the proposed technique less sensitive to the random noise inherent in digital images at extreme magnifications (a region of interest less than 10 μm). The method is implemented to document thermally-induced deformations of a microelectronics circuit. E-beam lithography is implemented using a standard SEM to fabricate regularly oriented patterns required for N-PRCT. The patterns are produced on a polished cross-section of a flip-chip package, and the package is subsequently subjected to a temperature excursion inside the SEM chamber. Thermal deformations are obtained in a region of interest of approximately 7 × 6 μm.     

面内和离面位移场的电子散斑（ESPI）自动检测技术研究

本文采用频域同态滤波技术，减少了电子散斑的噪声，得到高质量的条纹图，并介绍一种自行设计的新型相移器，它结构简单，性能稳定，测试精度高和操作方便，此外，应用以上两种技术，以承受均布载荷周边固定的圆板为例，实现了电子散斑三维位移场的自动测量，实验与理论值吻合良好。     

Measurement of Automotive-Suspension Displacement Using Rotary Variable Differential Transformers

Experimental Techniques -     

Depth-resolved Imaging and Displacement Measurement Techniques Viewed as Linear Filtering Operations

The last 5 years have seen the emergence of a family of optical interferometric techniques that provide deformation measurements throughout three-dimensional (3-D) weakly scattering materials. They include wavelength scanning interferometry (WSI), tilt scanning interferometry (TSI), phase contrast spectral optical coherence tomography (PC SOCT) and hyperspectral interferometry (HSI) and can be thought of as a marriage between the phase sensing capabilities of Phase Shifting Interferometry and the depth-sensing capabilities of Optical Coherence Tomography. It was recently shown that some closely related 3-D optical imaging techniques can be treated as shift-invariant linear filtering operations. In this paper, we extend that work to include WSI, TSI, PC SOCT and HSI as spatial filtering operations and also relate the properties of their transfer functions in the spatial frequency domain to their spatial resolution and phase sensitivity, for depth-resolved displacement measurements.     

基于Haar小波变换的位移场测量方法

本文提出了一种应用小波变换对固体表面位移场进行测量的新方法，在图像分析时，用各点属于不同尺度的小波变换系数来表征该点周围的子区。将试件表面位移前后的两幅数字图像进行小波变换，通过变形前后两幅图像小波变换系数之间的相互匹配，使位移前后两幅图中的子区对应起来，从而确定图像的位移场。本文应用Haar小波变换进行了计算机模拟实验和实物位移实验。引入亚像素技术，获得了0．02的位移测量精度。     

虚位移场方法在石墨材料力学参数测量中的应用

光测实验技术在现代力学研究中得到了广泛的应用。对于材料力学参数如杨氏模量和泊松比的测量,可利用典型加载试验如拉伸试验、弯曲试验并结合光测方法(如云纹和数字图像相关技术)得到位移值,利用载荷信息和应变场信息通过计算获得相关的力学参数。本文利用虚位移场方法测量石墨材料的力学参数。结合石墨材料的三点弯曲实验,由数字图像相关法测量得到试件表面的非均匀变形场。通过选择两组不同的虚位移场,可以反算出材料的力学参数:杨氏模量和泊松比。结果表明这种方法可以有效测量石墨材料的弹性参数。该方法可望在材料力学行为检测中得到推广应用。     

Hydrodynamic and Geometric Stiffening Effects on the Out-of-Plane Waves of Submerged Cables

This study focuses on the relative importance of two sources of nonlinearities affecting submerged cable response. The first of these is the added fluid damping offered by the surrounding medium while the second is the geometric stiffening offered by the cable through finite extensions of its centerline. The contribution of each nonlinear effect, taken separately and in tandem, is evaluated herein through the study of structural waves that form in the (out-of-plane) direction normal to the cable equilibrium plane.Numerical solutions are pursued herein using a finite difference algorithm which is brought to bear on two nonlinear cable/fluid models including: (1)~a nonlinear submerged cable model in which hydrodynamic drag is the sole nonlinear mechanism (referred to herein as the 'nonlinear drag model'); and (2)~a nonlinear submerged cable model in which hydrodynamic drag and geometric stiffening are both active nonlinear mechanisms (the 'nonlinear elastic-drag model'). Numerical solutions for propagating cable waves are developed for the case of a long suspension subjected to a concentrated harmonic excitation source. Conclusions are subsequently drawn regarding the spatial decay of the resulting out-of-plane waves and the dynamic cable tension induced by these waves. The effect of these two nonlinear mechanisms is further explored through the analysis of two additional, linear models: (3)~a simple linear taut string model without drag (the 'simple model'); and (4)~a linear taut string model with linear drag (the 'linear drag model'). The results of all models are critically compared and the range of validity of the linear/cable fluid models are assessed.     

Displacement and Strain Measurement by Circular and Radial Gratings Moiré Method

Direct digital moiré method of circular and radial gratings with its phase shifting technique is proposed and applied in a mixed-mode fracture problem of large deformation materials. Circular and radial curves are used as both reference and specimen gratings in this digital moiré method for deformation measurement. And phase shifting technique is automatically implemented directly on circular and radial fringes, which facilitates obtaining displacement fields in polar coordinate system, radial u _r and circumferential u _θ , and strain fields ε _r, ε _θ , ε _rθ are calculated subsequently. Application of the direct digital moiré method of circular and radial gratings in a mixed-mode fracture problem with large deformation illustrates the process of this method, and also demonstrates its feasibility and validity for large deformation materials.     

On the Displacement of NAPL Lenses and Plumes in a Phreatic Aquifer

The movement of an LNAPL lens above a sloping or horizontal water table, and a DNAPL lens above an impermeable surface is discussed. The governing equations are derived, using the vertical equilibrium approach and assuming the water mobility to be much greater than that of the NAPL. Analytical solutions are obtained for onedimensional movement of a lens along a sloping water table. They describe the lens movement with the formation of a jump at the leading front (large-scale approximation), and the distribution of NAPL in the transition zone near the jump (smallscale approximation). A model,describing the movement of a lens, taking into account NAPL retention,is proposed. Approximate onedimensional solutions for the movement of a NAPL lens along sloping or horizontal surfaces under such conditions are presented for this model. Some approximate analytical solutions for twodimensional lens (plume) formation and movement are obtained for the case of a point source at a sloping surface.     

二维数字图像相关测量中离面位移引起的误差分析

二维数字图像相关方法作为一种非接触全场变形测量的光学方法,在工程上有着广泛的应用.由于其假设物体只发生面内位移,而实验中往往存在离面位移,从而引起测量误差.本文针对这一问题利用了针孔模型,从理论上分析了离面位移对普通镜头测量结果的影响,通过铝块平移实验验证了理论分析的正确性.利用提出的理论模型修正橡胶材料的变形测量结果,并与远心镜头测量结果进行对比,发现修正后的普通镜头测量的结果更接近远心镜头测量的结果.最后,本文根据理论分析和实验验证,给出了减小或消除离面位移造成误差的方法.     

Identification of Mechanical Properties by Displacement Field Measurement: A Variational Approach

We study a parameter identification problem associated with a two-dimensional mechanical problem. In the first part, the experimental technique of determining the displacement field is briefly presented. The variational method proposed herein is based on the minimization of either a separately convex functional or a convex functional that leads to the reconstruction of the elastic tensor and the stress field. These two reconstructed fields are continuous and piecewise linear on a triangulation of the two-dimensional domain. Some numerical and experimental examples are presented to test the performance of the algorithms.     

Real-Time Displacement Measurement of a Flexible Bridge Using Digital Image Processing Techniques

In this study, real-time displacement measurement of bridges was carried out by means of digital image processing techniques. This is innovative, highly cost-effective and easy to implement, and yet maintains the advantages of dynamic measurement and high resolution. First, the measurement point is marked with a target panel of known geometry. A commercial digital video camera with a telescopic lens is installed on a fixed point away from the bridge (e.g., on the coast) or on a pier (abutment), which can be regarded as a fixed point. Then, the video camera takes a motion picture of the target. Meanwhile, the motion of the target is calculated using image processing techniques, which require a texture recognition algorithm, projection of the captured image, and calculation of the actual displacement using target geometry and the number of pixels moved. Field tests were carried out for the verification of the present method. The test results gave sufficient dynamic resolution in amplitude as well as the frequency. Use of this technology for a large suspension bridge is discussed considering the characteristics of such bridges having low natural frequencies within 3 Hz and the maximum displacement of several centimeters.     

考虑弯曲刚度斜拉索面内面外内共振分析

本文研究桥梁工程中含弯曲刚度斜拉索的面内面外内共振问题．描述了工程中斜拉索变形的三种状态,考虑弯曲刚度、大变形及垂度等因素,忽略斜拉索纵向惯性力的影响,运用Hamilton变分原理建立了含弯曲刚度的斜拉索面内面外耦合偏微分控制方程,采用Galerkin方法对偏微分方程离散,并运用多尺度摄动方法进行了求解,获得了斜拉索可能存在的内共振模式,以工程中一根斜拉索为例,运用有限元法对其进行动力特性分析,列出了斜拉索前10阶面内面外振动频率,找出面内面外可能产生内共振的模态,分别研究了主共振条件下斜拉索面内和面外1:1、2:1内共振情形,获得了有意义的结论．