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Showing papers on "Digital image correlation published in 2021"


Journal ArticleDOI
TL;DR: In this article, the use of distributed optical fiber sensors (DOFS) based on Optical Frequency Domain Reflectometry of Rayleigh backscattering for Structural Health Monitoring purposes in civil engineering structures is investigated.
Abstract: This paper investigates the use of distributed optical fiber sensors (DOFS) based on Optical Frequency Domain Reflectometry of Rayleigh backscattering for Structural Health Monitoring purposes in civil engineering structures. More specifically, the results of a series of laboratory experiments aimed at assessing the suitability and accuracy of DOFS for crack monitoring in reinforced concrete members subjected to external loading are reported. The experiments consisted on three-point bending tests of concrete beams, where a polyamide-coated optical fiber sensor was bonded directly onto the surface of an unaltered reinforcement bar and protected by a layer of silicone. The strain measurements obtained by the DOFS system exhibited an accuracy equivalent to that provided by traditional electrical foil gauges. Moreover, the analysis of the high spatial resolution strain profiles provided by the DOFS enabled the effective detection of crack formation. Furthermore, the comparison of the reinforcement strain profiles with measurements from a digital image correlation system revealed that determining the location of cracks and tracking the evolution of the crack width over time were both feasible, with most errors being below +/- 3 cm and +/- 20 mu m, for the crack location and crack width, respectively.

72 citations


Journal ArticleDOI
TL;DR: In this article, the authors focused on the analysis of fracture processes in fly ash (FA) concrete considering the second model of cracking, where the basic parameter of fracture mechanics in concrete elements according to Mode II fracture, i.e., KIIc, was determined using the Digital Image Correlation (DIC) technique.

71 citations


Journal ArticleDOI
TL;DR: In this article, an ML-based framework is proposed to predict the evolution of local strain distribution, plastic anisotropy and failure during tensile deformation of AlSi10Mg aluminum alloy produced by selective laser melting (SLM).

70 citations


Journal ArticleDOI
TL;DR: In this paper, the mechanical and fracture properties of basalt fiber reinforced fly ash geopolymer concrete with different length (3mm, 6mm, 12mm and 18mm) were investigated by means of compressive strength test, splitting tensile strength test and three point bending test.

50 citations


Journal ArticleDOI
TL;DR: In this article, the effect of different fiber/matrix materials on the damage progression of quasi-isotropic laminates with one open hole was investigated first and then, different hole orientations with respect to load direction were studied next to identify the damage mechanism of laminated composites with two interacting holes.

39 citations


Journal ArticleDOI
TL;DR: In this paper, a variational asymptotic homogenization of a 2D-continuum model describing large elastic planar deformations of a discrete bi-pantographic structure is presented.

38 citations


Journal ArticleDOI
TL;DR: In this paper, a 2D digital image correlation (2D-DIC) method was applied to measure the full-field strain in granite samples with different loading amplitudes, and the threshold value for rock fragmentation under ultrasonic vibration was obtained, and it was also found that the logarithm of the time required to meet this value decreases linearly with an increasing amplitude coefficient.
Abstract: Ultrasonic vibration-assisted rock breaking is a potentially effective technique to accelerate hard rock drilling processes. Fatigue damage is a primary factor that governs rock fragmentation subject to ultrasonic vibration, and when such damage accumulates to a critical level via crack initiation and propagation, macro-damage (e.g., macro-cracks) will occur. To date, however, the specific fatigue damage mechanism of hard rock materials under high-frequency and low-amplitude cyclic loading conditions is still unclear. In the present study, we applied a 2D digital image correlation (2D-DIC) method to measure the full-field strain in granite samples with different loading amplitudes. From these deformation data, the threshold value for rock fragmentation under ultrasonic vibration was obtained, and it was also found that the logarithm of the time required to meet this value decreases linearly with an increasing amplitude coefficient. Then, we conducted numerical simulation based on a 2D particle flow code (PFC2D) to reproduce the crack initiation and propagation processes and explore their mechanisms. The results from the simulation show that due to irreversible sliding under ultrasonic vibration, the difference in the displacement between particles on either side of a crack tip will increase, which leads to an increase in the concentrated lateral tensile stress. When the tensile stress exceeds the strength limit, the crack will initiate and propagate, resulting in fragmentation of rocks.

36 citations


Journal ArticleDOI
TL;DR: This study presents the first comprehensive literature review on remote deformation measurement in the presence of discontinuities using images, and different methodologies to overcome the limitation of DIC are analysed and categorized systematically.

36 citations



Journal ArticleDOI
TL;DR: In this paper, the inverse finite element method (iFEM) is applied to real-time displacement reconstruction of a moderately thick wing-shaped sandwich structure via a network of strain sensors.

30 citations


Journal ArticleDOI
TL;DR: In this article, the authors apply Digital Image Correlation (DIC) to X-ray computed tomography (CT) slices for characterization of individual fibers misalignment in continuous fiber composites.
Abstract: We apply Digital Image Correlation (DIC) to X-ray Computed Tomography (CT) slices for characterization of individual fibers misalignment in continuous fiber composites. This is an atypical application of DIC since the input is slices of a CT tomogram acquired at one time step, whereas the input of the typical deformation analysis application is 2D images captured over consecutive loading steps. The methodology is demonstrated and validated on synchrotron CT images of a glass/epoxy laminate, where individual fibers can be clearly identified. It is found that the average/standard deviation of the DIC displacement field in every CT slice is a good estimation of the average/standard deviation of the actual displacement of all fibers’ cross-sections in that slice. This provides a shortcut to the measurement of the moments of fiber orientation distribution, compared to the algorithms that reconstruct the fiber center lines. Using this shortcut, the fiber misalignment was also characterized in synchrotron CT images of a carbon/epoxy laminate, where individual fibers were not clearly observed and where, fiber segmentation tools failed to characterize the fibers. Furthermore, being applied to synchrotron images acquired during in-situ tension, the methodology is employed to quantify the evolution of misalignment during tension. The investigated 3D volumes are provided in [1] and described in [2].

Journal ArticleDOI
TL;DR: In this paper, a critical review of in situ full-field measurements provided by digital image correlation (DIC) for inspecting and enhancing additive manufacturing (AM) processes is presented.
Abstract: This paper is a critical review of in situ full-field measurements provided by digital image correlation (DIC) for inspecting and enhancing additive manufacturing (AM) processes. The principle of DIC is firstly recalled and its applicability during different AM processes systematically addressed. Relevant customisations of DIC in AM processes are highlighted regarding optical system, lighting and speckled pattern procedures. A perspective is given in view of the impact of in situ monitoring regarding AM processes based on target subjects concerning defect characterisation, evaluation of residual stresses, geometric distortions, strain measurements, numerical modelling validation and material characterisation. Finally, a case study on in situ measurements with DIC for wire and arc additive manufacturing (WAAM) is presented emphasizing opportunities, challenges and solutions.


Journal ArticleDOI
TL;DR: In this paper, a specific anisotropic elastic model for a WAAM-processed austenitic stainless steel was proposed, considering an orthogonally aisotropic constitutive law and a procedure to calibrate the elastic parameters based on experimental results.
Abstract: Wire-and-Arc Additively Manufactured (WAAM) alloys are characterized by specific mechanical properties which can largely differ from the conventionally-manufactured alloys. In detail, the printing process results in a peculiar microstructure, characterized by preferential crystallographic orientation with reference to the printing direction, that leads to an anisotropic mechanical behavior of the printed part. Previous experimental tests on WAAM-produced stainless steel plates showed in particular a strong anisotropic elastic behavior. Based on the above, the present work formulates a specific anisotropic elastic model for a WAAM-processed austenitic stainless steel, considering an orthogonally anisotropic (or orthotropic) constitutive law and a procedure to calibrate the elastic parameters based on the experimental results. In detail, the procedure is applied to calibrate the numerical values of the elastic parameters of a specific WAAM 304L austenitic stainless steel. For this aim, specific investigations on both the mechanical and microstructural features were carried out. Experimental tensile tests were performed on specimens with different orientations with reference to the printing direction. In detail, Young’s modulus and Poisson’s ratios were evaluated for samples oriented along three different orientations with regard to the printing deposition layers: longitudinally (L), transversally (T) and diagonally (D) to them. Digital Image Correlation (DIC) optical measuring system was used to acquire the full strain fields during the test. Microstructural analysis was also carried out to study the inherent microstructure, characterized by a distinctive grain growth direction, and to assess the preferred crystallographic orientations of specimens extracted along the three considered directions. The experimental results are used to calibrate the orthotropic elastic model. From the calibrated model additional material properties in terms of Young’s and shear modulus for any printing direction are derived. The resulting values exhibit very large variations with the printing angle, with ratios between minimum to maximum values around 2 for the Young’s modulus and 3.5 for the shear modulus. This marked orthotropic behavior could open unexplored design possibilities based on deformability issues. Additionally, the calibrated orthotropic model can also be used for future experimental explorations of the mechanical properties of WAAM alloys and for stiffness-based structural design optimizations.

Journal ArticleDOI
Liping Yu1, Bing Pan1
TL;DR: Challenges and recent advances in high-temperature DIC techniques are comprehensively summarized, to build a suitable DIC system for kinematic field measurements at high temperatures and solve the challenging problems that may be encountered during real tests.
Abstract: Developments in digital image correlation (DIC) in the last decade have made it a practical and effective optical technique for displacement and strain measurement at high temperatures. This overview aims to review the research progress, summarize the experience and provide valuable references for the high-temperature deformation measurement using DIC. We comprehensively summarize challenges and recent advances in high-temperature DIC techniques. Fundamental principles of high-temperature DIC and various approaches to generate thermal environment or apply thermal loading are briefly introduced first. Then, the three primary challenges presented in performing high-temperature DIC measurements, i.e., 1). image saturation caused by intensified thermal radiation of heated sample and surrounding heating elements, 2) image contrast reduction due to surface oxidation of the heated sample and speckle pattern debonding, and 3) image distortion due to heat haze between the sample and the heating source, and corresponding countermeasures (i.e., the suppression of thermal radiation, fabrication of high-temperature speckle pattern and mitigation of heat haze) are discussed in detail. Next, typical applications of high-temperature DIC at various spatial scales are briefly described. Finally, remaining unsolved problems and future goals in high-temperature deformation measurements using DIC are also provided. We expect this review can guide to build a suitable DIC system for kinematic field measurements at high temperatures and solve the challenging problems that may be encountered during real tests.

Journal ArticleDOI
TL;DR: In this paper, a non-linear 2D material model was implemented in ABAQUS and validated with extensive experimental test data from compression and tensile tests, which was recorded by a stereo camera system for digital image correlation to resolve damage initiation and propagation in detail.
Abstract: The limited capability to predict material failure in composite materials and specifically in wavy composite layers has led to high margins of safety for the design of composite structures. Thus, the full lightweight potential of this class of materials is left unused. To understand the complex failure behavior of composite materials containing out-of-plane fiber waviness under compressive and tensile loading, a non-linear 2D material model was implemented in ABAQUS and validated with extensive experimental test data from compression and tensile tests. Each test was recorded by a stereo camera system for digital image correlation to resolve damage initiation and propagation in detail. This study has shown excellent agreement of numerical simulations with experimental data. In a virtual testing approach various parameters, i.e. amplitude, wavelength and laminate thickness, have been studied. It was found that the failure mode changed from delamination to kink shear band formation with increasing laminate thickness. The wavelength has shown minor influences compared to amplitude and laminate thickness.

Journal ArticleDOI
TL;DR: The constitutive behavior of a near α Ti3Al2.5V alloy, conceived for impact resistant turbine engine containment applications, is characterized at quasi-static, medium, and high strain rates ranging from 10−3 [s−1] to 106 [s −1] by using the cylindrical compression specimen and shear compression specimen.

Journal ArticleDOI
TL;DR: Using digital image correlation (DIC) analysis in an Fe-19Cr-13Ni-0.2C austenitic stainless steel (mass), the tensile deformation behavior accompanied with the Portevin-LeChatelier (PLC) effect was investigated at high temperatures of 723-823 K under various applied strain rates of 10−4 s−1 −1 −5 −5 × 10−3 s− 1.

Journal ArticleDOI
TL;DR: In this article, a new DIC-based method is proposed for automatically tracing the discontinuities and quantitatively identifying the crack mechanism, i.e. mode I, mode II, and mixed-mode I/II.
Abstract: As a representative non-interferometric optical technique, the digital image correlation (DIC) can provide full-field displacement and strain measurement for the deformed rocks. However, the standard DIC technique has a limitation in measuring the displacements at the discontinuity and cannot be directly used for identifying the crack mechanism. Thus, a new DIC-based method is proposed for automatically tracing the discontinuities and quantitatively identifying the crack mechanism, i.e. mode I, mode II, and mixed-mode I/II. The new method involves three steps, including displacement measurement from the standard DIC technique, displacement field reconstruction at the discontinuity with the modified subset splitting technique, and post-processing for crack identification and displacement jump measurement. The effectiveness and robustness of the modified subset splitting technique and post-processing method have been verified with the synthetic images and theoretical displacement fields of mode I crack and dislocation. Then, the proposed method is utilized to locate cracks and quantitatively identify the crack mechanism of the initiated cracks in red sandstone containing a single flaw under uniaxial compression. The crack development in the flawed red sandstone specimens is analyzed and the crack types are summarized, in which wing cracks are in mode I, while horsetail cracks and anti-wing cracks are identified as mixed-mode I/II crack. It is shown that the new method avoids some ambiguous identification of crack mechanism and present more objective results.

Journal ArticleDOI
Xiang Zou1, Bing Pan1
TL;DR: An efficient, robust and full-automatic initial guess approach combining the speeded-up robust features (SURF) algorithm and the reliability-guided displacement tracking (RGDT) strategy is proposed, which can not only automatically select and update seed point, but also can effectively deal with target images with large deformation and rotation.

Journal ArticleDOI
TL;DR: In this paper, the auxetic cellular structures with two different chiral geometries (tetrachiral and hexachiral) were fabricated using laser powder bed fusion (LPBF) technology from two different materials (aluminium alloy AlSi10Mg and stainless steel AISI 316L).
Abstract: The auxetic cellular structures with two different chiral geometries (tetrachiral and hexachiral) were fabricated using laser powder bed fusion (LPBF) technology from two different materials (aluminium alloy AlSi10Mg and stainless steel AISI 316L). The specimen's microstructure, porosity and surface texture were observed by X-ray diffraction, optical and electron microscopy and micro-computed tomography. The mechanical properties of all specimens were determined experimentally with a simple tensile test. The results show that hexachiral and tetrachiral auxetic structures have similar initial stiffness, whereas the former provides a more ductile response with more than four times larger failure strain. The AISI316L steel provides for a much more ductile response than AlSi10Mg at comparable normalised load-carrying capability. The samples' deformation behaviour was analysed with the digital image correlation and tracking method, where it was shown that hexachiral samples exhibit a lower Poisson's ratio. The experimental results were used to validate the corresponding computational models, providing a more detailed analysis of deformation behaviour. They allow for cost-effective parametric studies and the development of new optimised chiral geometries.

Journal ArticleDOI
TL;DR: In this article, a series of semi-circular bending (SCB) tests were performed to examine the mode I fracture behavior of compacted MTs at different notch depths, and the digital image correlation (DIC) technique was utilized to acquire the surface image sequence under mode I loading condition in order to characterize the strain behaviors.

Journal ArticleDOI
TL;DR: In this article, the authors applied the particle displacement trend method to explain the initiation mechanism of secondary cracks, but the corresponding analyses are only reasonable if particle information along the y-axis is considered, and the simulation results prove that the Mode II and III failures are usually coupled, and direct Mode III failures only occur in the front and rear surrounding rocks of the preset flaw.
Abstract: Open flaws without any filling material are common fracture structures in real rock. To study the failure characteristics of this fracture structure, small-scale rock-like samples with single internal 3D open flaws are prepared, and uniaxial compression tests are conducted. Digital image correlation (for surface strain and failures) and acoustic emission (for internal microfracture behaviors) monitoring technologies are also employed to analyze the flaws. The test results are verified through numerical simulations. Different inclination angles of the internal preset flaws are found to have little influence on the strength of the samples, and the surface and internal secondary failures of the samples exhibit very different development processes and distributions. The particle displacement trend method is applied to explain the initiation mechanism of secondary cracks, but the corresponding analyses are only reasonable if particle information along the y-axis is considered. Therefore, the particle information in the y-axis is incorporated by defining new 2D sections (with y-axis) or partial 3D models. Based on these research methods, the initiation mechanism of secondary cracks is reasonably explained, and the influence of the preset flaw thickness on the particle displacement trend fields and secondary failures in surrounding rocks can be discussed. Finally, the simulation results prove that the Mode II and III failures are usually coupled, and direct Mode III failures (displacement of two parts of rock parallel to each other and in opposite directions) only occur in the front and rear surrounding rocks of the preset flaw.

Journal ArticleDOI
05 Jan 2021
TL;DR: Experiments show that the depth and height measurements of both techniques can reach sub-micron accuracy, and the relative accuracy of the 3D shape or position measurements can reach 1/600 000.
Abstract: With ever-increasing demand for three-dimensional (3D) imaging and shape measurements in a variety of fields, measurement accuracy has become of vital importance to numerous scientific and engineering applications. This paper presents an experimental investigation into the accuracy comparison of two prevalent 3D imaging and shape measurement methods: fringe projection profilometry (FPP) and 3D digital image correlation (3D-DIC) techniques. A detailed description of their principles reveals their inherent similarities and fundamental differences. A measurement system composed of both techniques is employed in the study, and a test target with speckle checkerboard patterns on its surface is adopted to allow simultaneous FPP and 3D-DIC measurements. The evaluation puts emphasis on how the geometric angles between key hardware components affect the 3D measurement accuracy. Experiments show that the depth and height measurements of both techniques can reach sub-micron accuracy, and the relative accuracy of the 3D shape or position measurements can reach 1/600 000.

Journal ArticleDOI
TL;DR: In this paper, a mesh-free non-ordinary state-based peridynamics (PD) technique is developed for simulating the elasto-plastic deformation of 3D polycrystalline aggregates of a magnesium alloy.

Journal ArticleDOI
TL;DR: In this article, a β-metastable Ti-alloy is designed with the aim to obtain a TWIP alloy but positioned at the limit between the TRIP/TWIP and the TWIP dominated regime.
Abstract: A new β-metastable Ti-alloy is designed with the aim to obtain a TWIP alloy but positioned at the limit between the TRIP/TWIP and the TWIP dominated regime. The designed alloy exhibits a large ductility combined with an elevated and stable work-hardening rate. Deformation occurring by formation and multiplication of {332} twins is evidenced and followed by in-situ electron microscopy, and no primary stress induced martensite is observed. Since microstructural investigations of the deformation mechanisms show a highly heterogeneous deformation, the reason of the large ductility is then investigated. The spatial strain distribution is characterized by micro-scale digital image correlation, and the highly deformed regions are found to stand at the crossover between twins, or at the intersection between deformation twins and grain boundaries. Detailed electron back-scattered imaging in such regions of interest finally allowed to evidence the formation of thin needles of stress induced martensite. The latter is thus interpreted as an accommodation mechanism, relaxing the local high strain fields, which ensures a large and stable plastic deformation of this newly designed Ti-alloy.


Journal ArticleDOI
TL;DR: In this paper, a multiscale model based on finite element analysis is proposed which includes repeating unit cell micromechanics, material nonlinearity, and progressive damage analysis to predict the mechanical behavior and failure of glass/carbon fiber hybrid composites subjected to various loading conditions.

Journal ArticleDOI
TL;DR: In this article, the behavior of short-length PLA 3D printed elements under compression is investigated, with a specific focus on buckling, and the experimental results are compared with three analytical models for buckling prediction in isotropic materials and with linear and non-linear Finite Elements (FE) models.
Abstract: In this work, the behaviour of short-length PLA 3D printed elements under compression is investigated, with a specific focus on buckling. An extensive experimental campaign is conducted on square polymeric columns produced via Fused Filament Fabrication (FFF), with the longitudinal axis oriented in the out-of-plane direction in 3D printing coordinate system. Compressive and tensile mechanical properties of FFF 3D printed PLA are determined; an asymmetry in out-of-plane tensile-compressive behaviour is discussed. The compression of the specimens is monitored using a single camera Digital Image Correlation system, supported by a preliminary validation of its set-up. The slenderness ratio at which the elements start to buckle is identified. The experimental results are compared with three analytical models for buckling prediction in isotropic materials and with linear and non-linear Finite Elements (FE) models. For a broad range of slenderness ratio, the tangent modulus theory gave a good, if conservative, estimation of the critical loads when used with the compressive mechanical properties. Furthermore, the predictions of the non-linear FE models were found to be consistent with the experimental results.

Journal ArticleDOI
TL;DR: In this paper, a 3D digital image correlation (DIC) is applied to evaluate stress-strain diagrams for welded joints in two different ways: the first one is based on measures strains along the welded joint, including all 3 zones of interest, base metal (BM), weld metal (WM), and heat-affected-zone (HAZ) subdivided into fine grain (FG) and coarse grain (CG) subzones.