共查询到20条相似文献,搜索用时 31 毫秒
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Two new techniques making use of the scattered-light speckle pattern have been developed which yield the displacements on an arbitrary interior plane of a 3-D body. When a sheet of coherent light passes through a transparent 3-D body, a small fraction is scattered. This scattered light produces a speckle pattern in an imaging system. By recording two superimposed images of this speckle pattern, one before and one after body deformation, the displacements on the interior illuminated plane can be found. The technique of scattered-light photography uses a single illuminating beam and is sensitive to displacements greater than one speckle diameter, approximately 3 μm. Scattered-light speckle interferometry uses two illuminating beams and is sensitive to displacements greater than one half the wavelength of light being used, approximately 0.2 μm. With both techniques, the double-exposed speckle photograph is optically processed to yield displacement information. With both techniques, the maximum displacement measurable is limited by correlation requirements between the two speckle patterns. Experimental results are presented demonstrating the two new techniques. 相似文献
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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. 相似文献
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本文用数字散斑相关方法测量了五种不同幂硬化指数韧性金属材料(铝和铜),双边裂纹尖端细观区域内应变场.对所得结果用韧性损伤模型进行了分析.在此法中以金属自然表面结构为散斑场,不同加载状态的散斑场进行比较,得到相对变形与应变.图象之间相关性 C 是变形参数或是位移及其导数的泛函.使其相关性 C 取最大值的试凑变形即为其真实变形场.这一方法在细观测量中应用得到满意的结果. 相似文献
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Impact-induced transient deformation analysis by means of digital speckle pattern interferometry 总被引:1,自引:0,他引:1
Transient in-plane displacements generated in a metal plate subjected to impact loading are measured using a pulsed digital
speckle pattern interferometry system. Two separated speckle patterns produced by a ruby laser that freezes the object motion
are recorded using a CCD camera and stored in a frame grabber. Transient displacements are evaluated by digital analysis of
the fringes generated by the subtraction of these speckle patterns. The computer used for image processing is also utilized
to control image acquisition and to synchronize the laser pulses to the CCD camera and the object position. Experimental results
are compared with numerical calculations obtained using the finite-element method. 相似文献
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R. V. Goldstein V. M. Kozintsev A. V. Podlesnykh A. L. Popov D. A. Chelyubeev 《Mechanics of Solids》2008,43(4):662-670
Advancement of nanomechanics and nanotechnologies assumes creation of adequate tools for measuring displacements in the nanoscale range. In the present paper, for these purposes we propose to use the method and hardware of electronic speckle interferometry, which have several advantages over the other known measurement means. We present an idea based on which the method of electronic speckle interferometry, primarily designed to be used to measure displacements in the submicron range, can be used to measure displacements that are hundreds of times smaller, i.e., of the order of 1 nanometer. We consider the theoretical justification of this idea and the program algorithm for its implementation and describe the methods, the test specimens, and the results of experimental metrological test of the possibility of measuring displacements in the nanoscale range by using the existing model of the electronic speckle interferometer. 相似文献
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H.-M. Zhu Y.-Y. Wu W.-H. Zheng Z.-W. Huang 《Archive of Applied Mechanics (Ingenieur Archiv)》2006,75(8-9):521-526
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. 相似文献
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通过对散斑计量法原理分析、数学描述及观测实例的论述,证明激光散斑法是研究煤矿地下结构物相似模型变形状态的一种新的无损检测技术,若采用白光作为光源,该项技术可用于二维变形场的实地测试。 相似文献
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A close-range objective white light speckle method has been used for strain determination on simply curved surfaces. The speckle
field is not the artificially printed random dots but only the radiance distribution of object surface which was slightly
treated before the test to produce fine structure of optical details. The holographic film, instead of holographic plate,
is attatched to the curved surface when illuminated by a flash light. Whole field fringe patterns are obtained with high sensitivities
and large adjustable range. There is no longer a requirement to derive the speckle movement on the image plane from the object
surface. Defocusing problem has been avoided. It can be practically applied to engineering problems with considerable convenience
because of the very simple recording system and little demand for environmental stability. 相似文献
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一种通过条纹方向图提取散斑条纹中心线的方法 总被引:3,自引:2,他引:1
在光测力学中,如何从单幅散斑干涉条纹图中消除散斑噪声,高精度自动提取相位信息,是一项较困难的工作。本文提出了一种计算条纹方向的简单算法,以及通过条纹方向图提取散斑条纹中心线的方法。实验表明此方法对高噪声的散斑条纹图非常有效。 相似文献
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激光散斑位移测量法是一种重要的现代光学位移测量方法,由于受到图像传感器元件感光性能限制,难以在强干扰光条件下获得有效散斑场信息,进而无法获取位移场数据,因此,基于单像素成像技术,本文提出一种新的激光散斑位移测量方法:对散斑信息进行图案编码调制,并使用单像素探测器采集调制后的光强信息;利用Walsh-Hadamard Transformation(WHT)成像算法对散斑场图像进行重建;最后结合自相关算法确定物体的位移场信息。分别利用商业相机和单像素成像技术对散射介质的单轴微小位移进行测量,结果表明基于单像素成像技术的激光散斑位移测量技术可以获得较好的测量结果。相比于传统测量方法,基于单像素成像技术的激光散斑位移测量方法在复杂环境中具有一定的优势,可实现强光干扰下的位移场测量。 相似文献
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Quasi-static fracture in four-point-bend specimens of both brittle and ductile materials was examined using a method which required only photographic access to the specimen surface. Decorrelation of laser speckle patterns was used as a means to map out two-dimensional regions of high surface strain associated with crack propagation. ASTM A515 grade 70 steel was tested, at temperatures above and below its brittle-ductile transition temperature, by double-exposure speckle photography of the area ahead of the crack tip. The regions where the two speckle patterns were uncorrelated, determined by pointwise spatial filtering of the speckle interferograms, have been observed and are related to plastic deformation of the specimen surface near the crack tip. A subsequent comparison of the decorrelation zones resulting from brittle versus ductile states showed differences as expected in both zone size and shape. 相似文献
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The authors show a nondestructive method for obtaining the isochromatic and isoclinic fringes in a three-dimensional photoelastic
specimen. The basic idea is to delimit a slice between two plane laser beams. The properties of polarization of the scattered
light (Rayleigh's law) and the interference possibilities of the diffused beams are used. By introducing speckle pattern properties,
the correlation factor of the two scattered beams is similar to the illumination given in a plane polariscope for the investigation
of a slice (in a classical frozen-stress technique). The authors use a monochromatic laser beam, a CCD camera and a personal
computer. Because they cannot obtain the correlation factor directly, they do a statistical analysis of the speckle patterns.
The variance (function of the correlation factor) is computed from the light intensities of three images corresponding to
the speckle pattern for plane 1 alone, plane 2 alone, and both planes together. 相似文献
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数字图像相关测量的普及提出了建立散斑质量评价体系要求,即发展针对不同的数字散斑图能够评估测量精度的标准方法.其中,数字图像相关计算中插值误差引起亚像素位移系统偏差(插值偏差)的估计是评价散斑质量的重要参数,然而至今插值偏差与散斑图结构及其插值方法之间的深层机制仍然不明,而且缺乏快速有效的手段估计插值偏差的量级.基于傅里叶方法获得了插值偏差的解析表达式.在满足采样定理的情况下,对其简化得到了插值偏差的带限近似形式和正弦近似形式.插值偏差的正弦近似形式解释了插值偏差随亚像素平移呈正弦形式变化的现象.基于插值偏差的正弦近似公式,提出了决定插值算法用于相关匹配优劣的插值偏差核概念,它表征了插值算法对散斑图特定频率的偏差响应,插值偏差是由插值偏差核与图像功率谱乘积的积分决定的.基于理论分析,提出了一种通过散斑频谱和插值偏差核估计插值偏差的简便有效算法,较之于传统的散斑图平移方法有明显的速度优势.分析了模板大小对估计精度的影响,并通过模拟进行了验证.解释了插值偏差产生的深层机理,解决了长久以来插值偏差难以快速估计的问题.不仅可以用于插值偏差估计,也可以用于插值算法优化,滤波模板选取等问题.对建立散斑质量评价体系,从而制作方便用户的水转印标准散斑也有推动作用. 相似文献
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Electronic Speckle Pattern Interferometry (ESPI) provides a sensitive technique for measuring surface deformations. The technique
involves comparison of the speckle phase angles within surface images measured before and after material deformation. This
phase angle comparison requires that the speckle positions be consistent in all images. A lateral shift between image sets
of just one pixel substantially degrades ESPI measurements, while a shift of two or more pixels typically causes complete
decorrelation and compromises the measurement entirely. To prevent such rigid body motions, the specimen and the optical system
must be rigidly fixed. This requirement typically impedes use of the ESPI method in applications outside laboratories or where
it is necessary to remove the specimen from the optical setup between ESPI measurements. Here, Digital Image Correlation (DIC)
is used to track speckle motion caused by specimen displacement between ESPI phase stepped image sets. The measured image
set can then be mathematically shifted to restore the original speckle locations, thereby recorrelating the ESPI measurement.
Examples are presented where ESPI measurements are successfully made with specimen shifts over 60 pixels. 相似文献
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Electronic shearography (ES), a laser interferometry technique, has the potential for large-scale structural inspection and
for identifying cracks and strain anomalies. A system based on this technology could possibly be used for noninvasive inspection
of structures with high insensitivity and robustness. One major problem is the existence of largerigid body motions in typical
engineering structures such as bridges and high-rise buildings. These rigid-body motions are large enough to cause a complete
decorrelation of the characteristic speckle pattern that is obtained by illuminating the object surface. This nullifies any
possibility of interference between speckled images obtained at different stages of loading, as is necessary for interferometry
applications. A systematic study was conducted to characterize the speckle pattern obtained from typical civil structures
as a function of the illumination and imaging system. Experiments were carried out to quantify speckle decorrelation as a
function of object motion and instrumentation characteristics. A fracture mechanics based finite element (FEM) analysis was
carried out on an existing fractured bridge to determine the strains and displacements. The results of these studies were
subsequently used to define the parameters of a structural inspection system based on ES for field applications. 相似文献
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The paper describes a hybrid experimental and numerical method analysis of bodies. It consists of the experimental method of double-aperture speckle interferometry and the boundary-integral method. The interference patterns allowing evaluation of the displacement vector are obtained by the speckle interferometry. The boundary displacements obtained experimentally are conveniently used for the calculation of stresses in the body by the boundary-integral method. Some examples bear witness of the effectiveness and accuracy of the hybrid technique. 相似文献
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The speckle tomography technique is used for reconstructing both large-scale structures in turbulent flows and the microstructure of turbulence. The technique is based on multi-projectional line-of-sight speckle photography measurements with a subsequent computer-assisted tomographic reconstruction of the interior structure of the flowfield. The large-scale structure is reconstructed using the Radon integral equation, and the microstructure is analysed using a statistical approach and a novel Erbeck-Merzkirch integral transform. Digital speckle photography and speckle tomography methods are described. Numerical simulation of the optical technique is performed using digital ray tracing through a turbulent flowfield. The methods are illustrated by the 3D "averaged" temperature fields in turbulent convective flows obtained earlier and by the recent reconstruction of 3D correlation functions of density variations in turbulent flows. Local values of turbulence (Kolmogorov) microscale are evaluated using these correlation functions and the Erbeck-Merzkirch integral transform The precision of the reconstruction and the spatial resolution achieved are analysed. 相似文献