物体运动、变形及光波长变化时的激光散斑运动规律

被激光照明的漫射面,由漫反射在空间Fresnel区形成的光场,用Fresnel-Kirchhoff积分表示。利用统计的方法,考虑变化前后强度场的相关度,得到关于强度场变化的三个基本方程,从而导出了激光散斑运动的一般公式。考虑了散斑场的变化是由漫射物面运动和变形以及激光光波长变化所引起。     

Investigation on mechanism of plastic deformation by digital speckle pattern interferometry

An experimental scheme of digital speckle pattern interferometry using two electromagnetic shutters and a three-frame color image board is presented to measure two in-plane components of incremental displacement field of diffuse objects. The deformation of the entire process from initial elastic deformation to fracture can be observed by using a Magneto Optical (MO) disk that has enough memory to record the image data of the entire process. By this system, some tensile experiments are achieved to investigate the mechanism of plastic deformation. The experimental results show that plastic deformation of tensile deformation is nonuniform. The material deforms in the distribution of domains. In the domains, the main deformation is uniform shear and rotation. At the boundary of the domains, the deformation is very large normal strain. With load, both the range and mode of domains are changing. At the end of plastic deformation, only two domains become dominant, and fracture happens at the boundary of the two domains.     

边界元和激光散斑的子域杂交法

本文将计算力学的边界元法和实验力学的激光散斑法相结合用于求解受力物体的应力应变场。即用实验提供变形物体的真实边界条件,用数值方法进行求解。文中定义了虚边界的概念,并进一步提出了子域杂交法。同单纯数值计算和实验分析相比较,本文提出的方法无需构造力学模型,因而具有简单、可靠的特点,并可以更好地应用于实际问题。     

Nondestructive testing using temporal phase evaluation in speckle interferometry

A novel nondestructive testing (NDT) method is reported in which temporal evolution of the speckles in speckle interferometry is used to measure large object deformations. The basic principle of the method is that continuous object movement introduces fluctuations in the phase of the speckle and is recorded as intensity modulation. Acquiring a large number of frames of the object motion, the phase data for the whole object deformation are then retrieved by the Fourier transformation technique. The method is capable of measuring more than 100 μm in-plane and out-of-plane deformation with speckle interferometry and more than 500 μm for speckle shearing interferometry. The authors discuss the NDT results obtained with the three methods and make some relative comparisons of each.     

Elastic characterization of anisotropic materials by speckle interferometry

In this paper we present an experimental procedure for the elastic characterization of thin anisotropic plates. The procedure allows the determination of the elastic constants of isotropic materials (metals and ceramics) and orthotropic materials (composite laminae). Moreover, the flexural compliances of completely anisotropic uncoupled materials (most of composite laminates) can also be measured. The tests are carried out by applying a concentrated force to the specimen supported by three spheres. The stress components are evaluated by simply measuring the applied load, while the strain fields are measured by digital phase-shifting speckle interferometry. The experimental procedure is entirely controlled by a virtual instrument developed for this purpose in the National Instruments LabVIEW^® environment, which runs on a personal computer interfaced with a standard black and white CCD camera. By means of the speckle interferometer, the whole field of the out-of-plane displacements is acquired; the curvatures, and hence the strain components, are obtained by two subsequent numerical differentiations. The numerical processing of the experimental data was carried out in the Mathematica? environment. The results obtained on a steel specimen and on a composite laminate are reported.     

材料热膨胀系数的激光散斑干涉测量方法

采用激光散斑干涉法测量材料的热变形，利用已知热膨胀系数的材料作为标准试件，无需对温差进行精密测量。在相对简单的实验设备条件下，得到较高精度的材料热膨胀系数。     

钢纤混凝土裂纹尖端应变场的实验研究

本文应用散斑干涉技术在四组含纤量分别为０，０．５％，１％，１．５％的钢纤混凝土三点弯曲裂纹试件的裂纹尖端位移场进行了测试，并换算为应变场。对钢纤混凝土开裂的基理进行了探讨；验证了最大位应变准则；并测定断裂韧度Ｊｉｃ．     

激光散斑干涉法测量金属复合引线热膨胀系数的实验研究

本文采用激光散斑干涉法测量微电子金属封装用金属复合引线的热膨胀系数。该方法有很高的测量精度和灵敏度,并对试件形状、尺寸和表面无特殊要求。同时利用光学方法全场测量的优点,使用已知热膨胀系数的金属材料作为标准试件,可减少温度场不均匀分布及微小变化对测试精度的影响,消除了测量光路几何参数导致的系统误差。在相对简单的实验设备下,得到较高精度金属复合引线的热膨胀系数值。该方法可广泛用于各种新材料的热膨胀系数的测定。     

Deformation measurement of conducting polythiophene thin films by an electronic speckle pattern interferometric method

The deformation measurement of electrosynthesized polythiophene (Pth) thin films is difficult because of the small thickness and high flexibility of the specimen. An electronic speckle pattern interferometry (ESPI) method is used to measure the deformation of Pth films of thicknesses in the range of 4–65 μm. Their stres-strain curve are obtained. It is found that the mechanical properties of Pth films are sensitive to the specimen thickness. The tensile strength increases with decreasing thickness of thin film from 10 μm. The influence of the electrochemical synthesis conditions on the mechanical properties of Pth films is also discussed. Project supported by the Basic-Research Foundation of Tsinghua University (JC2000057), and the Visiting Scholar Foundation of Solid Mechanical Key Lab in Tongji University of the Ministry of Education of China. Received 10 September 2001; revision received 9 November 2001.     

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.     

光导纤维在近代光力学中应用的综述

本文综述了国内外光导纤维在全息干涉、散斑计量及云纹法中应用的历史和现状。光纤不仅可以作为柔性传光元件应用于近代光测力学,还可以用多模传象束传送物光波前,从而使得测量远方的或特殊环境下构件的位移场、应变场成为可能。     

双参考光全息—散斑干涉术的原理和实验

本文用统计光学方法对双参考光全息——散斑干涉术进行了详尽的理论分析,给出了全息和散斑干涉场区域平均光强分布与光学系统主要参数及三维变形场各分量之间关系的解析表达式,进而讨论了离面位移和面内位移测量的上、下限,最后还给出了有关的实验结果。     

Digital speckle correlation for strain measurement by image analysis

This paper is concerned with small strain measurement utilizing the numerical processing of digital images. The proposed method has its theoretical basis in digital signal analysis and, from a methodological point of view, it can be considered as an extension to digital images of the wellknown white light speckle photography technique. That conventional method is based on the analysis of photographic plates that are exposed twice (before and after the specimen deformation) with the image of a random speckle pattern that has been previously printed on the test piece surface. The digital speckle correlation advantages consist of requiring a very simple specimen preparation and, mainly, of allowing the strain field computation just by numerical elaboration of the acquired images. In this paper, the theoretical basis of the technique and some valuable improvements to the known analogous methodologies are presented. Finally, test results for an application of digital speckle correlation are shown and advantages and disadvantages of the technique are elaborated. In addition, further developments in this area are discussed.     

利用激光散斑相关的非接触式随机振动特性测量

所发展的测量随机振动的方法,是测量由物体表面一个点漫射形成的散斑场的相关统计特性.根据激光散斑运动规律,这个相关统计特性实时地反映该点的位移或转角的时间历程.由所记录的相关信息,通过频谱分析,可以得到运动的频城特性参数,这种方式是非接触式光测方法,对物体无任何附加质量的影响.本文以铜梁和钢梁为例.测量了冲击力作用下,梁的动态响应和频谱.     

Compression strain measurement by digital speckle correlation

In this paper, an optimized digital speckle correlation algorithm, named big-window correlation, is proposed to iterate strain directly. Verified by some experiments, the sensitivity and accuracy of the displacement gradient measurement with this method can be improved greatly. Finally, this method was applied to the measurement of the compression strain for polyurethane foam plastics materials. Then the material properties, such as the module of elasticity and the Poisson ratio, with different mass densities were obtained.     

超声波的光外差接收

激光接收超声是一种非接触式的超声接收技术，它在超声无损评估及检测领域有重要的应用。本文设计研制了激光外差干涉接收超声的实验系统，该系统由声光调制器产生光频的频移，锁相环进行位相解调。文中重点讨论：（１）在光学部分，外差干涉光路空间准直性对信噪比的影响。（２）在信号处理电路部分，锁相环电路特性分析及其参数确定     

Density-sensitive whole-field flow measurement by optical speckle photography

An optical whole-field, line-of-sight method is surveyed that allows the measurement of the refractive deflection angles of light transmitted through a flow with density changes. The method uses the principles of speckle photography. In comparison to classical optical methods such as interferometry, a much higher number of data values can be obtained from one record without the need of interpolating between experimental data. This high signal density is particularly advantageous for analyzing turbulent flows with density fluctuations. Such an analysis is, so far, restricted to the existence of axisymmetric turbulence. A number of applications to this type of turbulent flow are reported, and proposals are made for future developments that will allow this speckle technique to be applied to the study of turbulent shear flow.     

In-plane and out-of-plane displacement measurement by ultrasonic speckle correlation method (USCM)

When an object moves, ultrasonic speckles backscattered from its surface will follow the object to move. From the Kirchhoff diffraction theory and the correlation principles of random signals, the necessary condition for keeping the correlativity between the speckle fields before and after the objective displacement was deduced. Based on this condition, the formulas for the relationship between the speckle displacement and the objective displacement were obtained. Practical measurement was performed. Ultrasonic digital speckle correlation method was used to measure the in-plane displacement and out-of-plane displacement of an object. The displacements of the objective surface were evaluated after the displacements of the speckles were determined.This method can be also used to measure the displacements of an inner objective surface. A mountain-climbing search method was proposed, which enabled us to find the maximum correlation coefficient in the correlation operation quickly and efficiently. The experimental results showed good agreement with the theoretical predictions.     

数字散斑相关技术进展及应用

数字散斑相关技术是廿世纪末发展的一项光力学测量技术,历经20年各国学者的研究改进积累,目前已成为一种成熟的测量方法,并已成功地应用于力学测量中。本文回顾和叙述了这些进展,并列举在各方面的应用实例以进一步扩展其应用领域。数字散斑相关技术的八个关键问题即1.相关公式,2.搜索技术,3.亚像素搜索,4.散斑图,5.减噪,6.补偿技术,7.位移场至应变场转换,8.三维位移场测量。最后将叙述数字相关技术在材料测试、结构模型及实物监测、岩石力学、复合材料性能研究、生物力学等方面的广泛应用情况。     

Measuring displacement fields of curved surface by moire interferometry of partial coherent light

This paper presents a method to measure the in-plane displacement fields of curved surface by moire interferometry of partial coherent light. The method has the following advantages: simple optical system, no requirement on vibration isolation, high sensitivity, large measuring range, high contrast of interference fringes and availability to in situ structural testing. the present paper also gives theoretical analysis of the method and the formulas of light intensity and displacement field, and introduces a replication technique to form a high frequency reflectance grating on the curved surface. The expriments achieved the measurement of the surface displacement field of a cylindrical shell— the simultaneous circumferential, axial and 45° displacement fields. The torsional test data for surface displacement of a circular bar agree well with the theoretical result. The project supported by National Natural Science Foundation of China.