Showing papers on "Digital image correlation published in 2001"
TL;DR: An iterative, spatial-gradient based algorithm is developed, which uses only first-order spatial derivatives of the images before and after deformation, and an application of DISC to thermome- chanical diagnostics of electronic packaging is presented.
Abstract: Experimental solid mechanics relies heavily on surface dis- placement and deformation gradient measurements. Digital image/ speckle correlation (DISC) uses digital image processing to resolve dis- placement and deformation gradient fields. The practical implementation of DISC involves important challenges such as computation complexity and the discrepancy of the sensitivities and accuracies claimed in previ- ous studies. We develop an iterative, spatial-gradient based algorithm, which uses only first-order spatial derivatives of the images before and after deformation. Simulated images are then used to verify this algo- rithm, as well as to study the impact of speckle size on the accuracy. Based on these simulations, the sensitivity of DISC to displacement and deformation gradient, as well as an optimal speckle size for optimal ac- curacy, is recommended. The algorithm is then calibrated using rigid body translation and rotation, and an application of DISC to thermome- chanical diagnostics of electronic packaging is also presented. © 2001
390 citations
TL;DR: In this article, an imaging technique developed to study the strain localization phenomena that occur during the tension of thin, flat steel samples is presented, where the data are processed using digital speckle image correlation to derive the two in-plane components of the displacement vectors.
Abstract: This paper presents an imaging technique developed to study the strain localization phenomena that occur during the tension of thin, flat steel samples. The data are processed using digital speckle image correlation to derive the two in-plane components of the displacement vectors. The authors observe that the calculation of the intercorrelation function reveals a systematic error and propose a numerical method to limit its influence. Plastic incompressibility and thin-sheet assumptions are used to derive the third displacement component and, hence, the various strain and strain rate components. Numerous checks are presented at each step in processing the data to determine the final accuracy of the strain measurements. It is estimated that this accuracy is quite sufficient to track the inception and the development of localization. Examples of possible application are presented for mild steels whose strain localization mechanisms appear to be precocious and gradual.
298 citations
TL;DR: In this article, an experimental approach to discriminate models describing the mechanical behavior of polymeric materials is presented, where the authors focus on the particular case of hyper-elastic models to simulate the behavior of a rubber-like material.
Abstract: We present an experimental approach to discriminate models describing the mechanical behavior of polymeric materials A biaxial loading condition is obtained in a multiaxial testing machine An evaluation of the displacement field obtained by digital image correlation allows us to evaluate the heterogeneous strain field observed during these tests We focus on the particular case of hyper-elastic models to simulate the behavior of a rubber-like material Different expressions of hyper-elastic potential are used to model experiments under uniaxial and biaxial loading conditions
197 citations
TL;DR: Results from numerical and experimental studies using DC measurement data demonstrate that the approach can effectively isolate absorption and scattering heterogeneities, even for complex combinations of perturbations in optical properties.
Abstract: In this report, we present a method for reducing the inter–coefficient crosstalk problem in optical tomography The method described is an extension of a previously reported normalized difference method that evaluates relative detector values, and employs a weight matrix scaling technique together with a constrained CGD method for image reconstruction Results from numerical and experimental studies using DC measurement data demonstrate that the approach can effectively isolate absorption and scattering heterogeneities, even for complex combinations of perturbations in optical properties The significance of these results in light of recent theoretical findings is discussed
88 citations
TL;DR: In this paper, the relationship between surface and internal cracking was studied using high-resolution, non-destructive evaluation techniques to measure crack growth caused by compressive loading in the fracture process of cement-based materials.
Abstract: To study the relationship between surface and internal cracking, 2 high-resolution, non-destructive evaluation techniques were used to measure crack growth caused by compressive loading in the fracture process of cement-based materials. Digital image correlation (DIC) was used to characterize the 2-D, surface fracture pattern, while 3-D, internal behavior was measured with x-ray microtomography (XMT). Rectangular mortar specimens containing both sand and graphite aggregates were examined. These techniques gave complementary information about crack geometry and development: DIC was more effective at determining crack width and location of small cracks, while XMT depicted the shape of larger cracks more successfully and showed the influence of internal features on the fracture process. The effect of aggregate shape and strength and the subsequent influence of increased crack distribution on ductility are discussed.
77 citations
TL;DR: In this article, the authors describe the characteristics of the strain field within and outside of a propagating Luders band and the properties of strain states associated with diffuse and localised necking.
Abstract: The aim of this paper is to show that recent advances made in the field of speckle image processing give valuable information useful in understanding and modelling of localisation phenomena. The potentialities of the proposed imaging method are illustrated by examples extracted from tensile tests performed on steel specimens. Having introduced the underlying motivations of this experimental work, this paper briefly focuses on the image processing technique and its reliability. Then, it describes the characteristics of the strain field within and outside of a propagating Luders band. The properties of strain states associated with diffuse and localised necking are also investigated. The catalyst role of possible geometrical defects is pointed out. Finally, a method is proposed to construct, despite localisation, a local stress–strain correspondence.
72 citations
Abstract: Conductive fibers can reinforce concrete and monitor damage leading to the development of smart material. This research studied the correlation between the electrical and mechanical properties of cement composites reinforced with conductive carbon fibers. The tensile behavior and impedance behavior of extruded and notched composites with a fiber volume fraction of 0.5 and 3% were examined; mechanical load and electrical field were applied longitudinally. The crack growth of these composites during loading was observed and analyzed by digital image correlation. Impedance spectroscopy (IS) measurements were made under loaded and unloaded conditions to address the effect of specimen geometry, the manufacturing process, and the effect of fiber volume fraction. Using these IS measurements, along with numerical computation, the bridging area of the fibers could be extracted quantitatively from the tensile measurements. It is shown that such methods can be useful to elucidate the role of the reinforcing fibers during fracture.
72 citations
TL;DR: An edge-based image registration approach is developed to guide the intensity-based registration which uses optical flow estimation, and it is demonstrated that the approach proves useful for registering some multi-spectral images.
56 citations
24 Apr 2001
TL;DR: The two-photon image correlation spectroscopy (ICS) as mentioned in this paper was developed as an imaging analog of FCS optimized for measuring the aggregation state of fluorescently labeled macromolecules on the surface of biological cells.
Abstract: Image correlation spectroscopy (ICS) was developed as an imaging analog of fluorescence correlation spectroscopy (FCS) optimized for measuring the aggregation state of fluorescently labeled macromolecules on the surface of biological cells Ics was first implemented on a confocal laser scanning microscope (CLSM) and entails spatial autocorrelation analysis of fluorescence fluctuations within an image sampled from an area of the cell Spatial and temporal autocorrelation analysis of image time series enables measurement of both the molecular dynamics and aggregation state of the imaged molecules The parallel nature inherent in the collection of multiple fluctuations in an imaging scheme improves the signal to noise ratio of the correlation analysis, which enhances dynamic measurements for slowly moving species in membrane systems We outline our development of two-photon ICS and describe recent applications of the method for measurements of flow, diffusion and aggregation behavior of green fluorescent protein/integrin receptor constructs in living cells We also describe the use of two-photon excitation to perform two-color image cross-correlation spectroscopy to measure the dynamics and colocalization of non-identical species labeled with different fluorophores
42 citations
TL;DR: Results from displaced and thermally stressed microelectronic devices indicate these techniques can achieve comparable accuracies to other subpixel techniques and that the use of ANNs can facilitate very fast analysis without knowledge of the analytical form of the image correlation function.
Abstract: Microscopic deformation analysis has been performed using digital image correlation and artificial neural networks (ANNs). Cross-correlations of small image regions before and after deformation contain a peak, the position of which indicates the displacement to pixel accuracy. Subpixel resolution has been achieved here by nonintegral pixel shifting and by training ANNs to estimate the fractional part of the displacement. Results from displaced and thermally stressed microelectronic devices indicate these techniques can achieve comparable accuracies to other subpixel techniques and that the use of ANNs can facilitate very fast analysis without knowledge of the analytical form of the image correlation function.
40 citations
TL;DR: In this article, an image correlation method is proposed to track the displacement of the observed thermal pattern on the wall, which is similar to particle image velocimetry, but the thermal patterns on the heated wall are used, rather than tracing particles.
Abstract: This paper deals with measurements of convective velocity of large-scale thermal structures, using the thin foil technique and infrared thermography to visualize the thermal pattern on the wall. An image correlation method is proposed to track the displacement of the observed thermal pattern. The idea of the method is similar to that of particle image velocimetry, but the thermal patterns on the heated wall are used, rather than tracing particles. On this basis, the thermal patterns created by the coherent structures of turbulent channel flow are examined. Particular attention is paid to the determination of the optimal parameters of image acquisition, including spatial and temporal separation. An attempt is made to relate momentum and scalar transport analyses by considering the propagation velocity of large-scale temperature structures. The proposed technique appears to be an attractive alternative for non-intrusive analysis of turbulent flow, especially, where opaqueness of channel walls excludes the use of optical methods.
Patent•
21 May 2001
TL;DR: A reference image updating method and apparatus used in an image-correlation system which updates a reference image when predetermined control parameters are met is described in this article. But this method is not suitable for the case of static images.
Abstract: A reference image updating method and apparatus used in an image-correlation system which updates a reference image when predetermined control parameters are met. An image corresponding to a displacement of a surface is captured and stored. A reference image and the captured image are compared at different offsets in a displacement direction. When the displacement falls within set predetermined displacement values or a predetermined value for a sample time that corresponds to the displacement, then the reference image is updated. By updated the reference image in this manner, systematic errors are prevented from accumulating thereby significantly removing systematic errors in the image-correlation system.
TL;DR: In this paper, an experimental and analytical evaluation of the compressive response of two composite, notched stiffened panels representative of primary composite wing structure is presented, where a three-dimensional full-field image correlation technique is used to measure all three displacement components over global and local areas of the test panels.
Abstract: An experimental and analytical evaluation of the compressive response of two composite, notched stiffened panels representative of primary composite wing structure is presented. A three-dimensional full-field image correlation technique is used to measure all three displacement components over global and local areas of the test panels. Pointwise and full-field results obtained using the image correlation technique are presented and compared to experimental results and analytical results obtained using nonlinear finite element analysis. Both global and global-local image correlation results are presented and discussed. Results of a simple calibration test of this image correlation technique are also presented.
TL;DR: In this article, the transverse swelling behavior of tracheids of Douglas fir was observed with confocal scanning laser microscopy and DIC and succeeded in measuring the change of cell shape and distribution of expansion in cell walls with absorption of moisture.
Abstract: The swelling or shrinkage behavior of a cross section of wood is complicatedly affected by its anatomical structure and anisotropic elasticity. 1 Therefore, no theory that explains exactly the cause of swelling anisotropy has been reported. Recently, application of the digital image correlation method (DIC) to microscopic or mesoscopic strain measurements has been studied, 23 and DIC was found to be a promising tool for that purpose. We also observed the transverse swelling behavior of tracheids of Douglas fir by means of confocal scanning laser microscopy and DIC and succeeded in measuring the change of cell shape and distribution of expansion in cell walls with absorption of moisture. 4 However, the cross section surface planed by a sliding microtome was so smooth that we could not measure strain distribution in cell walls using DIC. In this study, therefore, the smooth surface of the cross section of cell walls was made rugged by sputter etching; and subsequently the minute swelling distribution of cell walls of latewood tracheids was observed with confocal scanning laser microscopy and DIC.
01 Jan 2001
07 Oct 2001
TL;DR: Displacement precisions of better than 0.03 pixels have been achieved by combining nonintegral pixel shifting of subimages and artificial neural networks (ANNs) trained to estimate the subpixel element of the object displacement from the digital correlation.
Abstract: Digital image correlation has been used to measure microscopic deformation in thermally stressed microelectronics devices. Displacement precisions of better than 0.03 pixels have been achieved by combining nonintegral pixel shifting of subimages and artificial neural networks (ANNs). The ANNs are trained to estimate the subpixel element of the object displacement from the digital correlation. Although similar accuracies can be obtained by curve-fitting to the correlation peaks and differentiating, the neural approach has the advantage that it allows fast subpixel. displacement analysis over a range of object textures without knowledge of the analytical form of the correlation peaks.
30 Oct 2001
TL;DR: In this paper, the authors present an approach to deformation measurement based on localized correlation analysis on load state images, which is applied to thermo-mechanical reliability studies on electronic packaging components.
Abstract: Recent advances in micro electronics and electronic packaging have led to a strong need in material characterization on micro and nano scale. The authors present an approach to deformation measurement based on localized correlation analysis on load state images. Displacement and strain fields are extracted from images, captured by high resolution equipment, e.g. by optical far distance, scanning electron and scanning force microscopes. As a result object response to mechanical or thermal load can be recorded from microscopic or nanoscopic material areas. Within the paper a brief overview is given about measurement basics, achievable measurement resolution and equipment. The method is being applied to thermo-mechanical reliability studies on electronic packaging components. As an example stress suppression mechanisms on advanced chip scale packages (CSP) have been investigated. Spatially resolved deformation measurement by correlation techniques could have been extended successfully to AFM imaging. A corresponding application is demonstrated for experiments on microcrack evaluation. In order to measure material properties a modified correlation algorithm is applied assuming homogeneous material response. Determining average strains over micrographs material properties as coefficients of thermal expansion (CTE) and Poisson ratios can be determined on micro objects.
Patent•
23 Mar 2001
TL;DR: In this paper, a method for measuring movement amount or a mobile speed by the use of mutual correlation of continuous images photographing a mobile body was proposed, in which a time mean brightness value of each image or a minimum brightness value in a time-based pickup image group is subtracted from an original image, so that a stationary body image is eliminated as noise, and mutual correlation is selectively left behind.
Abstract: PROBLEM TO BE SOLVED: To eliminate stationary subject image as noise from a recorded image to enhance measuring precision SOLUTION: In a method for measuring movement amount or a mobile speed by the use of mutual correlation of continuous images photographing a mobile body, a time mean brightness value of each image or a minimum brightness value in a time-based pickup image group is subtracted from an original image, so that a stationary body image is eliminated as noise, and mutual correlation of images, in which a mobile body image is selectively left behind, is taken
Patent•
07 Sep 2001
TL;DR: In this paper, a synthetic aperture radar device is provided with a transmit-receive antenna 1, a wide-band transmitter-receiver part 2 amplifying signals collected by the transmit- receive antenna 1.
Abstract: PROBLEM TO BE SOLVED: To heighten accuracy in estimating the phase compensation quantity to obtain an image improved in resolution by suppressing the error of image correlation caused by speckle noise. SOLUTION: This synthetic aperture radar device is provided with a transmit-receive antenna 1; a wide-band transmit-receive part 2 amplifying signals collected by the transmit- receive antenna 1; an image reproducing processing part 3 for carrying out image reproducing processing, using an output signal from the wide-band transmit-receive part 2; an azimuth FFT part 4 performing the inverse Fourier transformation of an image in the proceeding direction of a platform; a spectrum dividing part 5 for dividing the Fourier transformed result of the image equally in a plurality of parts; an azimuth IFFT part 6 for performing the inverse Fourier transformation of the divided result; a picture element neighborhood averaging part 10 for performing the neighborhood averaging of the adjacent picture elements of the image obtained by inverse Fourier transformation; an image correlation part 7 for computing the correlation in all combinations of a plurality of images in the neighborhood averaged result of the picture elements; a phase compensating part 8 for computing the phase compensation quantity from the correlative result of the images to compensate the phase, and an image reproducing part 9 for reproducing the image from the phase compensated result.
29 Jun 2001
TL;DR: In this article, the limitations of using assumptions of linearity, particularly in the case where image data is acquired before and after a change in optical properties within an object with heterogeneous optical properties, are explored.
Abstract: Image reconstruction and data collection in optical tomography can be achieved in a number of different ways. This paper explores the limitations of using assumptions of linearity, particularly in the case where image data is acquired before and after a change in optical properties within an object with heterogeneous optical properties. The effects of using a 2 dimensional (2D) reconstruction scheme for changes in 3D measurements are also demonstrated. Problems are a direct result of the inherent non-linearity of optical tomographic image reconstruction. We show how these assumptions affect images of changes in absorption in the presence of a) heterogeneous background scatter, and b) heterogeneous background absorption using both simulations and time-resolved experimental data. Comparisons of results using non-linear and linear image reconstruction techniques are included throughout. The origin and dependence of the error are investigated. Methods to improve results by using estimates of background structure from baseline images are shown to improve quantitation and object localization in simple images. The potential significance of this error is discussed in relation to successful, reliable clinical imaging of the neonatal brain.
TL;DR: In this paper, the homogenization of periodic and heterogeneous masonry structures like masonry, which is composed of stones linked by joints of mortar, was studied in order to study the mortar interface behavior.
Abstract: This work is part of a study of historical masonry behavior It deals with the homogenization of periodic and heterogeneous structures like masonry, which is composed of stones linked by joints of mortar Combined compressive-shearing tests were performed in order to study the mortar interface behavior Deformation properties were measured, locally, by an optical extensometer Like the speckle method, this principle uses digital image correlation processing Compared to the volume of the joint, the size of aggregates induces heterogeneities An experimental protocol is proposed to determine homogenous deformation according to joint width and localized deformation according to joint height This approach accurately characterizes the interface at a microscale level and enhances high compaction strain at the interface
13 Jun 2001
TL;DR: In this paper, a fractal correlation method of displacement measurement is developed to estimate the in-plane displacement field of a body, which is based on gray level correlation between unformed and deformed digital images.
Abstract: The classical digital speckle pattern, or digital image, correlation method of deformation measurement is based on gray level correlation between unformed and deformed digital images. Since the pattern of artificial random speckles and the natural texture have fractal characteristics, and their fractal dimensions represent both gray and morph information, a fractal correlation method of displacement measurement is developed in this paper. The in-plane displacement field of a body can be acquired. In order to verify the validity of the new method, an experiment has been designed and the results have been compared with those tested by gray correlation method. The calculation speed is over 20 times fast than the digital image correlation method. The results how that its precision is less than 0.05 pixels.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
20 Oct 2001
Patent•
07 Sep 2001
TL;DR: In this paper, a system and method are described for an image registration system, including a registration engine that receives complex image data for corresponding images, which generates a correlation map between the complex image pair for relative translation by calculating an inverse of the complex conjugate product of the first image and the frequency domain data of the second, corresponding image.
Abstract: A system and method are described for an image registration system and method including a registration engine that receives complex image data for corresponding images. The registration engine generates a correlation map between the complex image pair for relative translation by calculating an inverse of the complex conjugate product of the frequency data of the first image and the frequency domain data of the second, corresponding, image. The frequency domain data may be obtained using Fast Fourier transform-based techniques.
Patent•
01 Aug 2001
TL;DR: In this article, a single-lens instantaneous three-dimensional image taking apparatus that is used for taking digital image is described, which includes a lens installed inside the digital image-taking apparatus and arranged in a straight line, an aperture plate and a single sensor.
Abstract: This invention is about a single-lens instantaneous three-dimensional image taking apparatus that is used for taking digital image. In addition, the digital image taking apparatus includes a lens installed inside the digital image taking apparatus and arranged in a straight line, an aperture plate and a single sensor, wherein the aperture plate is defined with three apertures having different angular coordinates and deviated from the optical axis. The three apertures are provided with red, blue, and green color filters, respectively, for allowing the object light to pass through the lens, and the image of object is projected onto the sensor, so as to obtain the object image and the color information in three different angles. After that, color separation and image correlation techniques are used to obtain the precise three-dimensional measurement of the object and color information.
Dissertation•
01 Jul 2001
TL;DR: In this paper, a calibration has been performed on the existing scanning tunneling microscopy (STM) built "in-house" and the coefficients used in the STM system were confirmed.
Abstract: Probe microscopy (scanning tunneling microscopy and atomic force microscopy) and digital image correlation together serve as a potentially powerful tool for experimentally
investigating the mechanical behaviors of materials at the sub-micron and nanometer scales. Based on the tunneling effect in quantum physics, the scanning tunneling
microscope (STM) records surface topography quantitatively and can achieve angstrom resolution. The digital image correlation (DIC) extracts the displacements and gradients
from the undeformed and deformed topographical images.
In this work, a calibration has been performed on the existing STM built "in-house" and the coefficients used in the STM system were confirmed. Major improvements on several
components of the system have been made, including constructing a new actuator probe to decouple its in-plane and out-of-plane movements, designing and implementing a new
first-stage amplifier to reduce the noise output by a factor of 10 and modeling of the controller in the STM feedback loop.
Further, systematic study of the digital image correlation has been conducted. In the simple case of one-dimensional correlation, key parameters involved are the subset size,
variables in the displacement representation, frequency content of the signal and noise. The one-dimensional study was then extended to two dimensions. In addition to those
key parameters identified in the one-dimensional study, the sampling rate poses substantial influence on the correlation accuracy. Low amplitude, high frequency noise
still increases the correlation error significantly.
07 May 2001
TL;DR: This work uses bilinear time-frequency distributions and their optimized version by the AOK procedure to analyze experimental near-field optical and magneto-optical raw images and shows that this approach allows local characterization of optical resolution and separation of relevant optical information from artifacts caused by the scanning probe recording process.
Abstract: Near-field microscopy has been developed to characterize optical properties of materials below the diffraction limit. It consists of scanning a probe, which can be of atomic dimensions, a few nanometers above a material surface, and detecting electromagnetic interaction. The resulting near-field optical images are conventionally analyzed by means of Fourier-based methods although these data are nonstationary. This observation suggests that time frequency analysis is potentially a powerful tool for extracting attributes such as local resolution of near-field optical microscopes. We use bilinear time-frequency distributions and their optimized version by the AOK procedure to analyze experimental near-field optical and magneto-optical raw images. We show that this approach allows local characterization of optical resolution and separation of relevant optical information from artifacts caused by the scanning probe recording process.
Patent•
07 Dec 2001
TL;DR: In this article, the authors proposed a displacement detection method for estimating the sub-pixel displacement of an image in an image correlation position transducer with high speed and accuracy, and a reading head using it.
Abstract: PROBLEM TO BE SOLVED: To provide a displacement detection method for estimating the sub- pixel displacement of an image in an image correlation position transducer with high speed and accuracy, and a reading head using it. SOLUTION: A correlation value (sum of differences) between first and second images is calculated and plotted each time one pixel is shifted along the direction of displacement. The points of a relatively small number of correlation values in the vicinity of extreme values are used. Also, symmetrical points across extreme values of the points of specific correlation values are obtained by interpolation from the points of other correlation values, and mid-point positions with respect to these points are used as extreme values. Thus, the speckle image correlation position transducer can be formed which can detect displacement with high speed and accuracy through simple calculations, using the points of a relatively small number of correlation values.
13 Jun 2001
TL;DR: This paper presents a method of compensating for any vibration of the object under study and thus alleviating the adverse effects of vibration on the quality of fringe patterns obtained by DSSI by incorporating DIC Into D SSI before the image subtraction phase of the technique.
Abstract: Digital speckle shearing interferometry is an optical method for measuring displacement derivatives directly and has gained wide acceptance for many industrial applications. Although it has a reputation for being insensitivity o vibration, an unfavorable environment may cause severe deterioration of the typical double-eye fringe pattern, making interpretation difficult. Digital image correlation has been found to be capable of detection displacement os points on images of illuminated object surface to a high degree of accuracy. This is achieved through a relatively simple set-up. This paper presents a method of compensating for any vibration of the object under study and thus alleviating the adverse effects of vibration on the quality of fringe patterns obtained by DSSI. This is achieved by incorporating DIC Into DSSI before the image subtraction phase of the technique. It is shown that good quality fringes can be obtained successfully for specimens vibrating at 25 Hz with amplitudes of up to 1mm.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.