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‣ Displacement and strain field assessment of PDMS using digital image correlation

Mendonça, B.; Ribeiro, J.E.; Lopes, H.; Martins, P.; Vaz, M.A.P.; Gomes, S.
Fonte: Instituto Politécnico de Bragança Publicador: Instituto Politécnico de Bragança
Tipo: Conferência ou Objeto de Conferência
Português
Relevância na Pesquisa
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The main goal of this work is to characterize the hyper-elastic mechanical behaviour of PDMS. For that, were made-up special specimens of PDMS (Sylgard® 184) for test them in bi-axial tensile machine. During the tensile test was used a commercial digital image correlation system (ARAMIS of GOM) to obtain de displacement and strain fields. These measurements are compared with numerical simulations which uses the more popular algorithms of constitutive models.

‣ Displacement and strain full-field measurement at open hole composite specimen using the digital Image correlation technique

Ribeiro, J.E.; Lopes, H.; Pimenta, S.; Vaz, M.A.P.
Fonte: Instituto Politécnico de Bragança Publicador: Instituto Politécnico de Bragança
Tipo: Conferência ou Objeto de Conferência
Português
Relevância na Pesquisa
663.04016%
This work presents the analysis of the displacement and strain fields at open hole carbon epoxy composite specimen using the optical of Digital Image Correlation (DIC). An uniaxial tensile test with Hexcel IM7/8552 composite specimen that was previous drilled and created a random intensity pattern on its surface. During the test was captured a sequence of images using an equipment of commercial DIC system, the Aramis. The results were subsequently analyzed and was verified the possibility of damage detection using this technique.

‣ Displacement and strain field assessment of PDMS using digital image correlation

Mendonça, B.; Ribeiro, J.E.; Lopes, H.; Martins, P.; Vaz, M.A.P.; Gomes, Silva
Fonte: Instituto Politécnico de Bragança Publicador: Instituto Politécnico de Bragança
Tipo: Conferência ou Objeto de Conferência
Português
Relevância na Pesquisa
663.04016%
The main goal of this work is the characterization of the hyper-elastic mechanical behaviour of PDMS. The special specimens of PDMS (Sylgard® 184) were tested in a bi-axial tensile machine. During the tensile test was used a commercial digital image correlation system (ARAMIS of GOM) to obtain de displacement and strain fields. These measurements are compared with numerical simulations which use the most popular algorithms of constitutive models.

‣ On the analysis of notched concrete beams: From measurement with digital image correlation to identification with boundary element method of a cohesive model

FERREIRA, M. D. C.; VENTURINI, W. S.; HILD, F.
Fonte: PERGAMON-ELSEVIER SCIENCE LTD Publicador: PERGAMON-ELSEVIER SCIENCE LTD
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
663.04016%
A way of coupling digital image correlation (to measure displacement fields) and boundary element method (to compute displacements and tractions along a crack surface) is presented herein. It allows for the identification of Young`s modulus and fracture parameters associated with a cohesive model. This procedure is illustrated to analyze the latter for an ordinary concrete in a three-point bend test on a notched beam. In view of measurement uncertainties, the results are deemed trustworthy thanks to the fact that numerous measurement points are accessible and used as entries to the identification procedure. (C) 2010 Elsevier Ltd. All rights reserved.; FAPESP/CNRS

‣ Digital image correlation analysis of the load transfer by implant-supported restorations

TIOSSI, Rodrigo; LIN, Lianshan; RODRIGUES, Renata C. S.; HEO, Young C.; CONRAD, Heather J.; MATTOS, Maria da Gloria C. de; RIBEIRO, Ricardo F.; FOK, Alex S. L.
Fonte: ELSEVIER SCI LTD Publicador: ELSEVIER SCI LTD
Tipo: Artigo de Revista Científica
Português
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This study compared splinted and non-splinted implant-supported prosthesis with and without a distal proximal contact using a digital image correlation method. An epoxy resin model was made with acrylic resin replicas of a mandibular first premolar and second molar and with threaded implants replacing the second premolar and first molar. Splinted and non-splinted metal-ceramic screw-retained crowns were fabricated and loaded with and without the presence of the second molar. A single-camera measuring system was used to record the in-plane deformation on the model surface at a frequency of 1.0 Hz under a load from 0 to 250 N. The images were then analyzed with specialist software to determine the direct (horizontal) and shear strains along the model. Not splinting the crowns resulted in higher stress transfer to the supporting implants when the second molar replica was absent. The presence of a second molar and an effective interproximal contact contributed to lower stress transfer to the supporting structures even for non-splinted restorations. Shear strains were higher in the region between the molars when the second molar was absent, regardless of splinting. The opposite was found for the region between the implants, which had higher shear strain values when the second molar was present. When an effective distal contact is absent...

‣ Análise inversa utilizando o método dos elementos de contorno e correlação de imagens digitais; Inverse analysis utilizing the boundary element method and digital image correlation

Ferreira, Manoel Dênis Costa
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 13/07/2012 Português
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A identificação de parâmetros físicos e geométricos utilizando medições experimentais é um procedimento comum no tratamento de muitos problemas da ciência e engenharia. Neste contexto, a análise inversa apresenta-se como uma importante ferramenta no tratamento desses problemas. Este trabalho apresenta formulações que acoplam o uso do método dos elementos de contorno (MEC) e a técnica de correlação de imagens digitais (CID) (para obtenção dos campos de deslocamentos) na resolução de alguns problemas inversos de interesse para engenharia de estruturas. Implementou-se um código computacional baseado no MEC, em técnicas de regularização e em algoritmo genético, para análise inversa em problemas de identificação das propriedades dos materiais, recuperação das condições de contorno e identificação de parâmetros do modelo coesivo de fraturamento. Exemplos com dados oriundos de uma prévia análise direta (simulando dados experimentais) são apresentados para demonstrar a eficiência das formulações propostas. Ensaios de vigas em flexão em três pontos com entalhe foram realizados com aquisição de imagens para obtenção dos campos de deslocamentos da região de propagação da fissura, via CID. Estes campos foram utilizados para alimentar o modelo inverso proposto. A técnica de CID originou dados em quantidade e precisão suficientes para os fins almejados neste trabalho. A utilização do MEC mostrou-se simples e de grande eficiência para a solução dos problemas inversos tratados.; The identification of physical and geometrical parameters utilizing experimental measurements is a common procedure in treating many problems of science and engineering. In this context...

‣ Análise das tensões geradas por implantes curtos e convencionais reabilitados com próteses fixas unidas e isoladas, por meio do método de correlação de imagem digital; Analysis of the stresses generated by short and conventional implants rehabilitated with splinted and non-splinted fixed prosthesis by digital image correlation method

Peixoto, Raniel Fernandes
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 06/12/2013 Português
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Nos casos de perda óssea vertical severa, principalmente em áreas posteriores da mandíbula, o uso de implantes curtos associado a próteses fixas metaloplásticas esplintadas pode ser uma alternativa às cirurgias de enxerto ósseo e a melhor transmissão de tensões ao osso adjacente, respectivamente. Dentre os métodos que avaliam a distribuição de tensões em torno dos implantes, a Correlação de Imagem Digital (CID) leva vantagens no que diz respeito à possibilidade de avaliar a distribuição das tensões de forma contínua por meio de imagens obtidas ao longo do tempo, durante carregamento oclusal. Diante disso, este trabalho avaliou qualitativa e quantitativamente o desempenho biomecânico de próteses fixas metaloplásticas parafusadas, unidas e isoladas, sobre implantes de diferentes comprimentos, posicionados na região posterior da mandíbula, por meio do método de CID. A partir de quatro modelos mestres, foram confeccionados quatro modelos em resina de poliuretano F16, simulando extremidade livre mandibular, com o dente 44 em resina (Luxatemp) e os dentes 45, 46 e 47 substituídos por implantes curtos (4 x 5 mm) e/ou convencionais (4 x 11 mm). Os grupos (G) deste estudo foram: G1 (dois implantes convencionais [45 e 46] e um curto [47])...

‣ Application of digital image correlation in investigating the bond between FRP and masonry

Ghiassi, Bahman; Xavier, José; Oliveira, Daniel V.; Lourenço, Paulo B.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Publicado em //2013 Português
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Full characterization of the bond behavior between Fiber Reinforced Polymers (FRPs) and masonry in externally bonded reinforcement (EBR) technique is crucial at the design stage or structural performance prediction. In this regard, a full-field assessment technique seems to be valuable for an adequate characterization of the bond behavior. The digital image correlation (DIC) and feature tracking techniques have been used in this study for investigating the evolution of strains and deformation during uniaxial tensile tests and shear debonding tests in FRP-masonry systems. The results show that the DIC is a valuable technique for characterization of the bond behavior and investigating its three-dimensional aspects. The DIC was also found applicable for following the matrix crack development in Steel Reinforced Grout (SRG) specimens. Feature tracking method was used for monitoring the strains development on the steel fibers in SRG specimens during tensile tests.

‣ In-plane strain measurement by digital image correlation

Hung,Po-Chih; Voloshin,A. S.
Fonte: Associação Brasileira de Engenharia e Ciências Mecânicas - ABCM Publicador: Associação Brasileira de Engenharia e Ciências Mecânicas - ABCM
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/09/2003 Português
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This paper presents a "fast and simple" (FAS) detection algorithm based on the digital image correlation for measurement of the surface deformation of planar objects. The proposed algorithm uses only fine search at the pixel level resolution and surface fitting for sub-pixel level. Two different specimens are investigated to explore the feasibility of this proposed algorithm. The displacements calculated by the FAS algorithm are compared with the ones obtained from Newton-Raphson method (N-R) and Enhanced Sequential Similarity Detection Algorithm (ESSDA). The results show that the experimental data are in good agreement with the theoretical solution. The proposed algorithm is found to be much faster than Newton-Raphson method with inferior, yet reasonable, accuracy for displacement and strain evaluation in the cases of uniaxial tension and disk under diametrical compression tests.

‣ Experimental investigation of mixed-mode-I/II fracture in polymer mortars using digital image correlation method

Nunes,L.C.S.; Reis,J.M.L.
Fonte: Associação Brasileira de Ciências Mecânicas Publicador: Associação Brasileira de Ciências Mecânicas
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/03/2014 Português
Relevância na Pesquisa
667.8894%
The purpose of this work is to investigate experimentally the effects of mixed-mode I/II loading on the fracture behavior of polymer mortars. Three point bend beam specimens with offcenter notch were used in plane-strain fracture toughness tests. Two approaches have been simultaneously used to determine the crack opening displacements. The crack mouth opening displacement was measured by means of a clip gauge, while the crack tip opening displacement was estimated through the Digital Image Correlation method. Fracture parameters, such as critical values of crack opening displacement, energy release rate and mixed-mode stress intensity factor were estimated. In addition, the values of crack mouth opening displacement and crack tip opening displacement were used to evaluate the rotational factor. Finally, the effect of sliding mode-II in fracture was not easily observed using clip gage, however this effect was noticed employing Digital Image Correlation method.

‣ Spatiotemporal Image Correlation Spectroscopy (STICS) Theory, Verification, and Application to Protein Velocity Mapping in Living CHO Cells

Hebert, Benedict; Costantino, Santiago; Wiseman, Paul W.
Fonte: Biophysical Society Publicador: Biophysical Society
Tipo: Artigo de Revista Científica
Português
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We introduce a new extension of image correlation spectroscopy (ICS) and image cross-correlation spectroscopy (ICCS) that relies on complete analysis of both the temporal and spatial correlation lags for intensity fluctuations from a laser-scanning microscopy image series. This new approach allows measurement of both diffusion coefficients and velocity vectors (magnitude and direction) for fluorescently labeled membrane proteins in living cells through monitoring of the time evolution of the full space-time correlation function. By using filtering in Fourier space to remove frequencies associated with immobile components, we are able to measure the protein transport even in the presence of a large fraction (>90%) of immobile species. We present the background theory, computer simulations, and analysis of measurements on fluorescent microspheres to demonstrate proof of principle, capabilities, and limitations of the method. We demonstrate mapping of flow vectors for mixed samples containing fluorescent microspheres with different emission wavelengths using space time image cross-correlation. We also present results from two-photon laser-scanning microscopy studies of α-actinin/enhanced green fluorescent protein fusion constructs at the basal membrane of living CHO cells. Using space-time image correlation spectroscopy (STICS)...

‣ Detection and Correction of Blinking Bias in Image Correlation Transport Measurements of Quantum Dot Tagged Macromolecules

Durisic, Nela; Bachir, Alexia I.; Kolin, David L.; Hebert, Benedict; Lagerholm, B. Christoffer; Grutter, Peter; Wiseman, Paul W.
Fonte: The Biophysical Society Publicador: The Biophysical Society
Tipo: Artigo de Revista Científica
Português
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Semiconductor nanocrystals or quantum dots (QDs) are becoming widely used as fluorescent labels for biological applications. Here we demonstrate that fluorescence fluctuation analysis of their diffusional mobility using temporal image correlation spectroscopy is highly susceptible to systematic errors caused by fluorescence blinking of the nanoparticles. Temporal correlation analysis of fluorescence microscopy image time series of streptavidin-functionalized (CdSe)ZnS QDs freely diffusing in two dimensions shows that the correlation functions are fit well to a commonly used diffusion decay model, but the transport coefficients can have significant systematic errors in the measurements due to blinking. Image correlation measurements of the diffusing QD samples measured at different laser excitation powers and analysis of computer simulated image time series verified that the effect we observe is caused by fluorescence intermittency. We show that reciprocal space image correlation analysis can be used for mobility measurements in the presence of blinking emission because it separates the contributions of fluctuations due to photophysics from those due to transport. We also demonstrate application of the image correlation methods for measurement of the diffusion coefficient of glycosyl phosphatidylinositol-anchored proteins tagged with QDs as imaged on living fibroblasts.

‣ Image Correlation Microscopy for Uniform Illumination

Gaborski, Thomas R.; Sealander, Michael N.; Ehrenberg, Morton; Waugh, Richard E.; McGrath, James L.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /01/2010 Português
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Image cross-correlation microscopy (ICM) is a technique that quantifies the motion of fluorescent features in an image by measuring the temporal autocorrelation function decay in a time-lapse image sequence. ICM has traditionally employed laser-scanning microscopes because the technique emerged as an extension of laser-based fluorescence correlation spectroscopy (FCS). In this work, we show that image correlation can also be used to measure fluorescence dynamics in uniform illumination or wide-field imaging systems and we call our new approach uniform illumination image correlation microscopy (UI-ICM). Wide-field microscopy is not only a simpler, less expensive imaging modality, but it offers the capability of greater temporal resolution over laser-scanning systems. In traditional laser-scanning ICM, lateral mobility is calculated from the temporal de-correlation of an image, where the characteristic length is the illuminating laser beam width. In wide-field microscopy, the diffusion length is defined by the feature size using the spatial autocorrelation function (SACF). Correlation function decay in time occurs as an object diffuses from its original position. We show that theoretical and simulated comparisons between Gaussian and uniform features indicate the temporal autocorrelation function (TACF) depends strongly on particle size and not particle shape. In this report...

‣ The efficacy of image correlation spectroscopy for characterization of the extracellular matrix

Mir, Sadiq Mohammed; Baggett, Brenda; Utzinger, Urs
Fonte: Optical Society of America Publicador: Optical Society of America
Tipo: Artigo de Revista Científica
Publicado em 03/01/2012 Português
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Image correlation spectroscopy (ICS) is known to be a useful tool for the evaluation of fiber width in the extracellular matrix. Here we evaluate a more general from of ICS fit parameters for fiber networks and arrive at a means of quantifying the fiber density, pore size and length which facilitates the characterization of the extracellular matrix. A simulation package was made to create images with different structural properties of fiber networks such as fiber orientation, width, fiber density and length. A pore finding algorithm was developed which determines the distribution of circular voids in the image. Collagen I hydrogels were prepared under different polymerization conditions for validation of our pore size algorithm with microscopy data. ICS parameters included amplitude, standard deviation and ellipticity and are shown to predict the structural properties of fiber networks in a quantitative manner. While the fiber width is related to the ICS sigma; the fiber density relates to the pore size distribution which correlates with the ICS amplitude in thresholded images. Fiber length is related to ICS ellipticity if the fibers have a preferred orientation. Findings from ICS and pore distribution algorithms were verified for both simulated and microscopy data. Based on these findings...

‣ Image Correlation Method for DNA Sequence Alignment

Curilem Saldías, Millaray; Villarroel Sassarini, Felipe; Muñoz Poblete, Carlos; Vargas Vásquez, Asticio; Maureira Butler, Iván
Fonte: Public Library of Science Publicador: Public Library of Science
Tipo: Artigo de Revista Científica
Publicado em 27/06/2012 Português
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The complexity of searches and the volume of genomic data make sequence alignment one of bioinformatics most active research areas. New alignment approaches have incorporated digital signal processing techniques. Among these, correlation methods are highly sensitive. This paper proposes a novel sequence alignment method based on 2-dimensional images, where each nucleic acid base is represented as a fixed gray intensity pixel. Query and known database sequences are coded to their pixel representation and sequence alignment is handled as object recognition in a scene problem. Query and database become object and scene, respectively. An image correlation process is carried out in order to search for the best match between them. Given that this procedure can be implemented in an optical correlator, the correlation could eventually be accomplished at light speed. This paper shows an initial research stage where results were “digitally” obtained by simulating an optical correlation of DNA sequences represented as images. A total of 303 queries (variable lengths from 50 to 4500 base pairs) and 100 scenes represented by 100 x 100 images each (in total, one million base pair database) were considered for the image correlation analysis. The results showed that correlations reached very high sensitivity (99.01%)...

‣ DYNAMIC MONITORING OF RAIL AND BRIDGE DISPLACEMENTS USING DIGITAL IMAGE CORRELATION

Murray, Christopher
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado
Português
Relevância na Pesquisa
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Rail and bridge infrastructure assets are critical elements of Canada’s transportation network and their continued efficient and safe operation is necessary to ensure the nation’s economic livelihood. Monitoring technologies that can detect changes in performance as well as precursors to failure are an important element of ensuring this efficient and safe operation. Digital Image Correlation (DIC) is a monitoring technology that has the potential to provide critical data for infrastructure assessment and to replace various conventional sensors with one integrated monitoring solution. In this research, the accuracy of DIC is evaluated using numerical, laboratory and field-based experiments. The sources of error of particular relevance to dynamic measurement using DIC are identified as (i) bias error in the sub-pixel interpolation scheme, (ii) the ratio of sample rate to the frequency of the signal being monitoring and (iii) the signal to noise ratio. It is also shown that the chosen sub-pixel interpolation scheme can greatly affect the accuracy of dynamic measurements. The use of DIC was investigated for field monitoring of both horizontal and vertical railway displacements at sites with good and poor subgrade conditions under dynamic train loading. It is shown that there is a significant benefit to using an absolute displacement measurement system rather than a relative displacement measurement system as the former can capture irrecoverable rail displacements in both the vertical and horizontal directions. Finally...

‣ Digital Image Correlation for Evaluating Structural Engineering Materials

Dutton, MICHAEL
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado
Português
Relevância na Pesquisa
665.6535%
In the structural engineering community, a need exists for a non-contact two-dimensional measurement system which could provide information for field monitoring and greatly enhance the accuracy of numerical structural models. Recent advances have enabled the use of digital image correlation (DIC) to calculate the surface displacements of chosen targets in a series of digital images with a high degree of accuracy. Images are recorded during an experiment and are afterwards post-processed to find relevant information including, but not limited to, a) global displacement, b) relative displacement and c) changes in strain. In this research, a series of experiments were conducted to create measurement techniques for monitoring steel and reinforced concrete (RC) structures utilizing DIC. However, to ensure accurate DIC measurements, the addition of artificial texture from lightly applied spray paint on finished concrete was investigated and was determined to noticeably improve results. Furthermore, the placement of the digital camera relative to the structure being monitored was shown to control not only the desired field of view in the region of interest, but also the resulting image texture and DIC measurement accuracy. The DIC technique was applied to monitor and understand two important aspects of structural evaluation: a) the movement along shear planes and b) the evaluation of changes in strain due to curvature in beam elements. To monitor the change in crack width and slip...

‣ A space–time approach in digital image correlation: Movie-DIC

BESNARD, Gilles; GUERARD, Sandra; ROUX, Stéphane; HILD, François
Fonte: elsevier Publicador: elsevier
Português
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A new method is proposed to estimate arbitrary velocity fields from a time series of images acquired by a single camera. This approach, here focused on a single spatial plus a time dimension, is specialized to the decomposition of the velocity field over rectangular shaped (finite-element) bilinear shape functions. It is therefore assumed that the velocity field is essentially aligned along one direction. The use of a time sequence over which the velocity is assumed to have a smooth temporal change allows one to use elements whose spatial extension is much smaller than in traditional digital image correlation based on successive image pairs. This method is first qualified by using synthetic numerical test cases, and then applied to a dynamic tensile test performed on a tantalum specimen. Improvements with respect to classical digital image correlation techniques are observed in terms of spatial resolution.

‣ Assessment of Digital Image Correlation Measurement Accuracy in the Ultimate Error Regime: Main Results of a Collaborative Benchmark

AMIOT, fabien; BORNERT, michel; DOUMALIN, pascal; DUPRÉ, Jean Christophe; FAZZINI, marina; ORTEU, Jean José; POILANE, Christophe; ROBERT, laurent; ROTINAT, René; TOUSSAINT, Evelyne; WATTRISSE, Bertrand; WIENIN, Jean Samuel
Fonte: Wiley Publishing Ltd Publicador: Wiley Publishing Ltd
Português
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We report on the main results of a collaborative work devoted to the study of the uncertainties associated with Digital image correlation techniques (DIC). More specifically, the dependence of displacement measurement uncertainties with both image characteristics and DIC parameters is emphasised. A previous work [Bornert et al. (2009) Assessment of digital image correlation measurement errors: methodology and results. Exp. Mech. 49, 353–370] dedicated to situations with spatially fluctuating displacement fields demonstrated the existence of an ‘ultimate error’ regime, insensitive to the mismatch between the shape function and the real displacement field. The present work is focused on this ultimate error. To ensure that there is no mismatch error, synthetic images of in-plane rigid body translation have been analysed. Several DIC softwares developed by or in use in the French community have been used to explore the effects of a large number of settings. The discrepancies between DIC evaluated displacements and prescribed ones have been statistically analysed in terms of random errors and systematic bias, in correlation with the fractional part τ of the displacement component expressed in pixels. Main results are as follows: (i) bias amplitude is almost always insensitive to subset size...

‣ A novel course-fine search scheme for digital image correlation method

Zhang, Zhi-Feng; Kang, Yi Lan; Wang, Huai-Wen; Qin, Qing Hua; Qui, Yu; Li, Xiao-Qui
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Português
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As a well-established technique for measuring surface deformation, the digital image correlation method (DICM) has received wide application in experimental mechanics and structural analysis in recent years. One of the major challenges in practical applic