Showing papers on "Speckle imaging published in 1999"
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TL;DR: It is shown that a simple process such as multiple repetition of an anisotropic sine/cosine average filter produces the effect of an excellent automatic adaptive filter for filtering speckle-interferometric phase fringe patterns.
229 citations
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TL;DR: A phase-shifting out-of-plane speckle interferometer operating at 1 kHz for studying dynamic events based on a Pockels cell that is synchronized to a high-speed video camera to ensure that the phase shifting occurs between frames.
Abstract: We describe a phase-shifting out-of-plane speckle interferometer
operating at 1 kHz for studying dynamic events. The system is based
on a Pockels cell that is synchronized to a high-speed video camera to
ensure that the phase shifting occurs between frames. Phase
extraction is performed by use of a standard four-frame algorithm, and
temporal phase unwrapping allows sequences of several hundred absolute
(rather than relative) displacement maps to be obtained fully
automatically. The maximum theoretical surface velocity of 67
µm s-1 is a factor of 40 greater than can be
achieved with a speckle interferometer based on a conventional video
camera. We test the system using a target that is displaced with
constant speed in a direction normal to its surface by means of a
piezoelectric transducer. The system’s performance in a practical
situation is illustrated with measurements on a thin plate undergoing
out-of-plane deformation.
116 citations
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TL;DR: In this paper, the authors have discussed laser-based interferometric techniques for measurement of refractive index, temperature and temperature profile of burners with special emphasis on laser speckle techniques and Talbot Interferometric technique.
115 citations
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TL;DR: The roughness dependence of the intensity autocorrelation function is studied and utilized to characterize typical engineering surfaces with anisotropic roughness to show that an in-process surface inspection can be achieved by this method.
Abstract: The statistical properties of speckle patterns generated from a rough surface under a fully developed static speckle-pattern illumination are examined. The roughness dependence of the intensity autocorrelation function is studied and utilized to characterize typical engineering surfaces with anisotropic roughness. The speckle patterns under investigation are recorded by use of a CCD technique and are then analyzed by digital image processing algorithms to obtain a parameter that describes the surface roughness. It is shown that an in-process surface inspection can be achieved by this method.
90 citations
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TL;DR: Improved orbital elements for 22 binary systems are presented in this article, for 12 binary systems, masses are calculated using available trigonometric parallaxes and making certain assumptions regarding the mass ratio.
Abstract: Improved orbital elements for 22 binary systems are presented. For 12 systems, masses are calculated using available trigonometric parallaxes and making certain assumptions regarding the mass ratio. For the other 10 systems, provisional elements are provided that should provide relatively accurate ephemerides for the next decade.
88 citations
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TL;DR: The ESA Hipparcos satellite made measurements of over 12,000 double stars and discovered 3406 new systems as discussed by the authors, including a total of 11,687 "problem stars" that did not provide the classical parameters of separation and position angle (ρ, θ) but were the so-called problem stars, flagged "G, "O, "V, or "X" (field H59 of the main catalog).
Abstract: The ESA Hipparcos satellite made measurements of over 12,000 double stars and discovered 3406 new systems. In addition to these, 4706 entries in the Hipparcos Catalogue correspond to double star solutions that did not provide the classical parameters of separation and position angle (ρ, θ) but were the so-called problem stars, flagged "G," "O," "V," or "X" (field H59 of the main catalog). An additional subset of 6981 entries were treated as single objects but classified by Hipparcos as "suspected nonsingle" (flag "S" in field H61), thus yielding a total of 11,687 "problem stars." Of the many ground-based techniques for the study of double stars, probably the one with the greatest potential for exploration of these new and problem Hipparcos binaries is speckle interferometry. Results are presented from an inspection of 848 new and problem Hipparcos binaries, using both archival and new speckle observations obtained with the USNO and CHARA speckle cameras.
87 citations
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TL;DR: In this article, the authors used speckle pattern interferometry to measure both harmonic vibration and transient deformation in real-time with microsecond temporal resolution for the first time.
Abstract: To the best of our knowledge, transient deformations have been measured in real time with microsecond temporal resolution for the first time with speckle pattern interferometry. The short exposure period and high framing rate of a high-speed camera at as many as 40,500 frames per second allow low-power continuous-wave laser illumination and fiber-optic beam delivery to be used. We have applied the technique to measure both harmonic vibration and transient deformation.
84 citations
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30 Apr 1999TL;DR: A novel laser speckle strain gauge for evaluating mechanical microstrains in perfused and superfused vessel segments is presented and changes in the mechanical behavior due to disease can be evaluated.
Abstract: Changes in the ultrastructure of vascular tissue due to pathologies such as atherosclerosis may be manifested as subtle changes in the mechanical properties of the arterial wall. The ability to detect these changes is considered to be important in the early diagnosis of atherosclerosis. In order to evaluate the subtle viscoelastic properties of the arterial wall, a highly sensitive means of evaluating mechanical strain in the tissue is required. Herein we will present a novel laser speckle strain gauge for evaluating mechanical microstrains in perfused and superfused vessel segments. The strain gauge relies upon 2D frequency transforms of stacked speckle histories, which are time sequences of one dimensional views of the backscattered light stacked into a 2D array such that time is along the vertical axis and space is along the horizontal axis. The gauge can be made sensitive only to in-plane strains. Sensitivity of the gauge is on the order of single microstrain. By mechanically straining the vessel segments in a custom microtensile testing machine fitted with a high sensitivity load cell, mechanical constants of the vessel wall can be derived and changes in the mechanical behavior due to disease can be evaluated.
84 citations
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TL;DR: With temporal DSP the spatial resolution of the shape measurement is improved considerably compared with previously reported results with projected random patterns.
Abstract: Projected random patterns have been used to measure the shape of discontinuous objects. A sequence of independent random patterns are projected onto the object. These images are analyzed by use of the technique called temporal digital speckle photography (DSP) that is introduced here. With temporal DSP the spatial resolution of the shape measurement is improved considerably compared with previously reported results with projected random patterns. A calibration procedure is described that uses a sequence of independent random patterns to calibrate measurement volume. As a result, independent space coordinates for each subimage are obtained. The accuracy is of the order of 1/1000 of the field of view where a subimage size of 8 pixels seems to be a good compromise between reliability and spatial resolution. The technique is illustrated with a measurement of an electrical plug and a 9-V battery.
80 citations
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TL;DR: In this article, an optimized digital speckle correlation algorithm, named big-window correlation, is proposed to iterate strain directly, which can improve the sensitivity and accuracy of the displacement gradient measurement with this method.
Abstract: 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.
74 citations
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TL;DR: In this paper, two new techniques for spatial phase stepping using a computer-generated holographic optical element (HOE) are described, and implemented with electronic speckle pattern interferom- etry, although they could be applied to other optical metrology methods.
Abstract: We describe two new techniques for spatial phase stepping using a computer-generated holographic optical element (HOE). The techniques are implemented with electronic speckle pattern interferom- etry, although they could be applied to other optical metrology methods. The first technique uses an HOE that introduces a known phase step between the 61 diffracted orders, without being translated. The interfer- ence phase corresponding to object deformation can be calculated from a single TV frame, and the technique is therefore suitable for the mea- surement of transient deformations. We apply the technique to measure the phase changes caused by refractive index variations in an evolving thermal plume. The second technique requires the HOE to be used in conjunction with a phase grating. In this technique, the HOE and the phase grating are used sequentially for the two exposures required in speckle interferometry (made before and after object deformation) and is therefore suitable for making dynamic deformation measurements with a double-pulsed interferometer. A root mean square (rms) precision of 2p/20 rad for the phase measurements is obtained. © 1999 Society of Photo-Optical Instrumentation Engineers. (S0091-3286(99)00712-6)
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TL;DR: A quantitative relation between the decorrelation of the scattered light fields and the rate of corrosion is established in a theoretical model, based on the statistics of phase and reflectivity changes of point scatterers at the surface.
Abstract: The changes in the microtopography of a metal surface during a corrosion process are measured by decorrelation of the scattered speckle fields under coherent illumination. For that purpose a quantitative relation between the decorrelation of the scattered light fields and the rate of corrosion is established in a theoretical model, based on the statistics of phase and reflectivity changes of point scatterers at the surface. The speckle fields are recorded by a CCD camera and processed numerically in a computer, yielding the standard deviation of the topography changes with nanometer sensitivity. From the analysis of a series of images taken at equal time intervals during the corrosion process, the degree of interrelation among subsequent topography changes is calculated.
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TL;DR: A multiwavelength speckle pattern shearing interferometer for the determination of two-dimensional strain distributions based on simultaneous illumination of the object with three diode lasers that emit at different wavelengths between 800 and 850 nm is reported on.
Abstract: We report on the development of a multiwavelength speckle pattern shearing interferometer for the determination of two-dimensional strain distributions. This system is based on simultaneous illumination of the object with three diode lasers that emit at different wavelengths between 800 and 850 nm. Wavelength separation and image acquisition were performed with a special optical arrangement, including narrow-bandpass filters and three black-and-white cameras. The shearographic camera with a variable shearing element, in combination with the appropriate illumination geometry, permitted us to isolate all six displacement derivatives from phase-stepped fringe patterns. The optical system and the measurement procedure were validated with two different experiments. First, the shearographic sensor head was used for the determination of in-plane displacements, and, second, in-plane strain distributions of an aluminum block caused by temperature expansion were measured.
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TL;DR: A computer-generated holographic optical element with electronic speckle pattern interferometry is used to calculate the interference phase corresponding to the deformation of a test object from a single TV frame.
Abstract: We have used a computer-generated holographic optical element
(HOE) with electronic speckle pattern interferometry to calculate
the interference phase corresponding to the deformation of a test
object from a single TV frame. The HOE is a modified crossed phase
grating that introduces a known phase change between the ±1 diffracted
orders, without being translated. The progressive propagation of
transient mechanical waves was measured with an rms precision of
2π/30.
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TL;DR: A detailed theory and analysis of the influence of decorrelation due to longitudinal and lateral size of the speckles is presented and it is shown that the method can be used to measure small deformations with higher resolution.
Abstract: Recently, a new method to measure object shape and deformation with
temporal evolution of speckles in speckle interferometry was
reported. In this method, certain parameters, sensitive to shape or
deformation are changed continuously, and the fluctuations in the
irradiance of each speckle is recorded. The information over the
whole object deformation is retrieved by Fourier-transformation
techniques. We present a detailed theory and analyze the influence
of decorrelation due to longitudinal and lateral size of the
speckles. It is also shown that the method can be used to measure
small deformations (less than 5 µm) with higher
resolution. Further, the nonlinearity of the camera is shown to
enhance the sensitivity.
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TL;DR: 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 as mentioned in this paper.
Abstract: 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.
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TL;DR: In this article, a general Bayesian approach for the joint estimation problem of fixed aberrations, dynamic aberrants, and the object from phase-diverse speckle data that leads to a maximum a posteriori estimator is presented.
Abstract: In phase-diverse speckle imaging one collects a time series of phase-diversity image sets that are used to jointly estimate the object and each of the phase-aberration functions. Current approaches model the total phase aberration in some deterministic parametric fashion. For many imaging schemes, however, additional information can be exploited. Specifically, the total aberration function consists of the fixed aberrations combined with dynamic (time-varying), turbulence-induced aberrations, about whose stochastic behavior we often have some knowledge. One important example is that in which the wave-front phase error corresponds to Kolmogorov turbulence. In this context using the extra statistical information available may be a powerful aid in the joint aberration/object estimation. In addition, such a framework provides an attractive method for calibrating fixed aberrations in an imaging system. The discipline of Bayesian statistical inference provides a natural framework for using the stochastic information regarding the wave fronts. Here one imposes an a priori probability distribution on the turbulence-induced wave fronts. We present the general Bayesian approach for the joint-estimation problem of fixed aberrations, dynamic aberrations, and the object from phase-diverse speckle data that leads to a maximum a posteriori estimator. We also present results based on simulated data, which show that the Bayesian approach provides an increase in accuracy and robustness for this joint estimation.
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TL;DR: It is shown that the absolute phase change in each pixel may be unwrapped by use of the DSP result as an initial guess for an in-plane deformation, which results in a high fringe contrast even for deformations of several speckle diameters.
Abstract: The compensation of large in-plane motions in digital speckle-pattern interferometry (DSPI) with the use of digital speckle photography (DSP) is demonstrated. Ordinary recordings of DSPI are recombined and analyzed with DSP. The DSP result is used to compensate for the bulk speckle motion prior to calculation of the phase map. This results in a high fringe contrast even for deformations of several speckle diameters. In addition, for the case of an in-plane deformation, it is shown that the absolute phase change in each pixel may be unwrapped by use of the DSP result as an initial guess. The principles of this method and experiments showing the in-plane rotation of a plate and the encounter of two rounded plates are presented.
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TL;DR: A procedure that uses the Rician distribution to predict the intensity statistics of the light at the image center as a function of the number of corrected Zernike polynomials is provided.
Abstract: Adaptive optics systems allow us to retrieve high-spatial-frequency information that is preserved in the wave fronts distorted by the atmosphere. Although wave-front correction should be as complete as possible, only partial compensation is attainable in the visible. We provide a procedure that uses the Rician distribution to predict the intensity statistics of the light at the image center as a function of the number of corrected Zernike polynomials.
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TL;DR: Application of the nonstationary polarization modulation of a speckle pattern transmitted through a photorefractive crystal under the alternating electric field of a square-wave form to noncontact and highly sensitive measurements of a rough surface movement is suggested.
Abstract: We have observed the nonstationary polarization modulation of a speckle pattern transmitted through a photorefractive crystal under the alternating electric field of a square-wave form. A simple model based on Gaussian-beam propagation in the crystal with the diffusion type of nonlinearity is proposed to explain the main features of the experiment. Application of the phenomenon to noncontact and highly sensitive measurements of a rough surface movement is suggested.
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TL;DR: In this article, the 3D dynamical nature of speckles that are formed in free space and in Fourier transform and imaging systems is investigated within the paraxial approximation as represented by ABCD-matrix theory, exact expressions for the space-time-lagged intensity covariance that results from an in-plane translation, an out-of-plane rotation, or an inplane rotation of a diffuse scattering object that is illuminated by a Gaussian-shaped laser beam.
Abstract: Three-dimensional (3D) speckle dynamics are investigated within the paraxial approximation as represented by ABCD-matrix theory. Within the paraxial approximation, exact expressions are derived for the space–time-lagged intensity covariance that results from an in-plane translation, an out-of-plane rotation, or an in-plane rotation of a diffuse scattering object that is illuminated by a Gaussian-shaped laser beam. As illustrative examples we consider the 3D dynamical nature of speckles that are formed in free space and in Fourier transform and imaging systems. The spatiotemporal characteristics of the observed 3D speckle patterns are interpreted in terms of boiling, decorrelation, rotation, translation, and tilting. Experimental results, which support the quantitative theory, are presented and discussed.
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TL;DR: A simple geometrical model was developed for calculation of the contrast of a polychromatic image-plane speckle pattern from a source of light with high spatial coherence and its validity was established by comparison with an exact solution.
Abstract: A simple geometrical model was developed for calculation of the contrast of a polychromatic image-plane speckle pattern from a source of light with high spatial coherence. It is based on counting the number of independent speckle patterns that contribute to a given point in the image plane. This results in a simple equation for the contrast as a function of imaging geometry; relative orientation of the projection direction, observation direction, and specimen normal; bandwidth of the light source; and surface roughness. Its validity was established by comparison with an exact solution: rms errors in the calculated contrast were only 0.033 over a wide range of parameter values likely to be encountered in practice.
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TL;DR: A dual in-plane electronic speckle pattern interferometry system has been developed for in situ measurements, and the overall system is controlled by advanced software, which allows switching between the two perpendicular planes in quasi real time.
Abstract: A dual in-plane electronic speckle pattern interferometry (ESPI) system has been developed for in situ measurements. The optical setup is described here. The system uses an electro-optical switch to change between the illumination directions for x and y sensitivity. The ability of the electro-optic device to change the polarization of the laser light forms the basis of this switch. The electro-optic device is a liquid-crystal layer cemented between two optically flat glass plates. An electric field can be set up across the layer by application of a voltage to electrodes. The speckle interferometry system incorporates two additional liquid-crystal devices to facilitate phase shifting, and the overall system is controlled by advanced software, which allows switching between the two perpendicular planes in quasi real time. The fact that there are no moving parts is an advantage in any ESPI system for which mechanical stability is vital.
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TL;DR: In this paper, position angles and separations resulting from 2578 speckle interferometric observations of 590 binary stars are tabulated using the 66 cm refractor at the US Naval Observatory.
Abstract: Position angles and separations resulting from 2578 speckle interferometric observations of 590 binary stars are tabulated This is the third in a series of papers presenting measures obtained using the 66 cm refractor at the US Naval Observatory in Washington, DC, and covers the period from 1995 June through 1996 December Program stars range in separation from 02 to 43, with a limiting magnitude of V = 11 Random errors are estimated to be 170 mas in separation and 056/ρ in position angle, where ρ is the separation in arcseconds These are the first results acquired using an improved intensified CCD detector The new detector, in concert with an intensity-filtering technique applied in software, has permitted a 1 mag increase in dynamic range, to 35 mag, for pairs separated by about 2'' The instrumentation and calibration are briefly described, with an emphasis on the characteristics of the new detector The software filter used to increase the dynamic range is also described
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TL;DR: In this paper, the leakage flux from the surface by using Hall elements, on magnetic noises, on sub-micron deformations by Ar-laser speckle interferometry and on residual stresses by X-ray diffraction were investigated.
Abstract: Nondestructive evaluations of iron-based material (A533B) have been investigated on the leakage flux from the surface by using Hall elements, on magnetic noises, on sub-micron deformations by Ar-laser speckle interferometry and on residual stresses by X-ray diffraction. A high resolution and high sensitivity for spatial inhomogeneity observation were attained as small as 200μm for residual strains less than 0.5 %.
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15 Sep 1999TL;DR: In this article, a micro speckle interferometer for scaling down the object size to one millimeter is presented, and the deformation behavior of an X-shaped torsional spring with a width of 100 micrometer is characterized.
Abstract: Design, manufacturing and test of microcomponents generate new challenges for measurement techniques in general. The non- contacting operation of optical metrology makes it attractive to solve the task of measuring geometric quantities of microparts. So far, speckle interferometry (ESPI) is well established as a measuring tool for analyzing deformation, vibration and strain on a macroscopic level. This paper deals with possibilities and application limits of ESPI in the case of scaling down the object size below one millimeter. In a first part, both spatial resolution and displacement sensitivity of the technique are discussed. Theoretical considerations are shown together with experimental verification. Secondly, a micro speckle interferometer will be presented that has been built for the use with different microscopes. Its capabilities are demonstrated by a practical application. The microcomponent under investigation is a bulk micromachined gyroscope, a demanding object with respect to its multilayer design. Developments aim at increasing the spatial resolution step by step and results obtained with different field of view will demonstrate the progress. Finally, the deformation behavior of an X-shaped torsional spring with a width of 100 micrometer could be characterized.
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TL;DR: A novel fluid-velocimetry technique based on speckle interferometry that provides information about the velocity field for an out-of-plane component of a Rayleigh-Bénard convective flow is presented.
Abstract: We present a novel fluid-velocimetry technique based on speckle interferometry. The light scattered from an illuminated plane is recorded with a CCD camera at the same time as a speckled reference beam. Substraction of two nonsimultaneous frames provides information about the velocity field for an out-of-plane component. An application to a Rayleigh-Benard convective flow is given.
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TL;DR: The results of 1314 speckle interferometric observations of 625 binary stars, ranging in separation from 2 to 52 with a limiting secondary magnitude of V = 11, are tabulated in this article.
Abstract: The results of 1314 speckle interferometric observations of 625 binary stars, ranging in separation from 02 to 52 with a limiting secondary magnitude of V = 11, are tabulated. These observations were obtained using the 66 cm refractor at the US Naval Observatory in Washington, DC, with an intensified CCD detector. This is the fourth in a series of papers presenting measures obtained with this equipment and covers the period 1997 January 1 through December 31. Random errors for all measures are estimated to be 18 mas in separation and 057/ρ in position angle, where ρ is the separation in arcseconds.
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TL;DR: In this article, position angles and separations resulting from 2406 speckle interferometric observations of 547 binary stars are tabulated, with random errors estimated to be 14 mas in separation and 052/ρ in position angle, where ρ is the separation in arcseconds.
Abstract: Position angles and separations resulting from 2406 speckle interferometric observations of 547 binary stars are tabulated. This is the second in a series of papers presenting measures obtained using the 66 cm refractor at the US Naval Observatory in Washington, DC, with an intensified CCD detector. Program stars range in separation from 02 to 38, with Δm ≤ 2.5 mag and a limiting magnitude of V = 10.0. The observation epochs run from 1993 January through 1995 August. Random errors are estimated to be 14 mas in separation and 052/ρ in position angle, where ρ is the separation in arcseconds. The instrumentation and calibration are briefly described. Aspects of the data analysis related to the avoidance of systematic errors are also discussed.
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08 Feb 1999TL;DR: In this paper, a moving picture encoding technique is introduced to encode all of the sequential fringe patterns as one MPEG2 file, and the analysis of a huge volume of fringe patterns becomes easy, and subtle changes of fringe pattern can be observed clearly.
Abstract: Whole deformation processes and slipboard propagation of aluminum alloy in tensile experiments are directly observed on whole field in real time by dynamic speckle interferometry. In plastic deformation, an inclined white band appears. It sweeps the specimen surface repeatedly in a certain sped and band width along the tensile direction. Sometimes the inclined angle of the white band transfers symmetrically. With plastic deformation increasing, the band speed decreases gradually, and the specimen cracks finally at the position where the band stops. Transient process of the white band formation is captured with a high speed CCD camera. It is revealed that the white band is a sharp slip deforming region consisted of concentrated inclined fringes. An interesting phenomenon that the strain value at a point of the specimen surface changes like a stair shape is accounted by the sweeping movement of the slipboard. The moving picture encoding technique is introduced to encode all of the sequential fringe patterns as one MPEG2 file. By watching the moving picture, the analysis of a huge volume of fringe patterns becomes easy, and subtle changes of fringe patterns can be observed clearly.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.