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Plastic anisotropy of laser melting deposited Ti–5Al–5Mo–5V–1Cr–1Fe titanium alloy
摘要： Tensile tests of laser melting deposited Ti–5Al–5Mo–5V–1Cr–1Fe titanium alloy specimens in different orientations were conducted, which indicates significant plastic anisotropy of this material. Digital image correlation method added in-situ-tensile tests were carried out to investigate mechanical properties with respect to specified material structures. The results indicate that the plasticity properties of the thick columnar grain and that of other grains are significant different. Under the same stress level, the thick columnar grain yield firstly and bear the main plastic deformation of the whole specimen. The elasto-plastic Poisson's ratio of the thick columnar grains and that of other grains are also different. Tests on layer bands indicate that the coarser microstructures of the layer bands lead a stronger resistance to tensile plastic deformation, but a weaker resistance to shear plastic deformation. In addition, the direction of primary α laths on both sides of the layer bands may be different, and this has an obviously effect on the tensile plastic deformation of the specimen.
关键词： Digital image correlation method,Plastic anisotropy,Laser melting deposited,Titanium alloy,Mechanical properties
更新于2025-10-24 16:40:20
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An omnidirectional DIC system for dynamic strain measurements on soft biological parts to An omnidirectional DIC system for dynamic strain measurement on soft biological tissues and organs
摘要： A limitation to the potential use of inverse methods in identifying the spatially varying properties of biological tissues consists in obtaining the required set of experimental data. In fact, whereas on the numerical side there are almost no limits to complexity in terms of geometry and material behavior of the model, on the experimental side, the collection of full-field displacement and strain data over the full surface of complex 3D geometries still represents a challenge. To address this issue, this work proposes an omnidirectional-DIC method capable of obtaining full-field information over the entire surface of native intact biological parts undergoing large deformation. This is made possible by the use of a concave conical mirror that enlarges the field of view of a conventional binocular stereo-DIC system up to 360° × 320°. The pair of highly distorted panoramic scenes reflected by the conical mirror are then matched by using a novel iterative image deformation scheme. In particular, first, a robust feature-based algorithm is used to calculate the gross disparity between images, then, an iterative NURBS-based intensity interpolation scheme refines the correlation through a hybrid local-global DIC approach. The accuracy of the developed image matching scheme was evaluated on synthetically generated images simulating a large and heterogeneous deformation field. Then, the potential of the proposed omnidirectional-DIC method was tested with rubber analogs reproducing the most representative geometries and loading states involved in biological materials characterization. Finally, as an illustrative example of application, full-field DIC shape and deformation measurements was performed over a whole porcine eye tested in-vitro under reproduced physiological load.
关键词： Eye,Omnidirectional measurement,Finite deformation,Digital image correlation,Inflation test
更新于2025-09-23 15:23:52
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In-situ 3D shape and recession measurements of ablative materials in an arc-heated wind tunnel by UV stereo-digital image correlation
摘要： In-situ three-dimensional (3D) ablation shape and recession measurements of ablative materials of hypersonic vehicles in high-temperature wind tunnel tests are essential to understand the ablation performance of these materials, which can provide necessary information for better thermal protection system (TPS) design. In this work, a novel ultraviolet stereo-digital image correlation (UV stereo-DIC) technique is proposed for in-situ measurements of 3D ablation shapes and recession in ablation tests. Specifically, a self-developed UV stereo-DIC system, combing a monochromatic UV illumination, two bandpass filters and two UV cameras, is first established. Using the UV stereo-DIC system, strong thermal radiation emitted from the heated sample and the heating device can be effectively suppressed. Natural textures formed from illuminating the rough sample surface by UV light are used as speckle patterns in stereo-correlation. In-situ 3D ablation shapes of a blunt cone subjected to arc heating were measured with a temperature range of 1000 °C to 1868 °C, and the UV stereo-DIC measurements showed good agreement with post-test measurement of the recession of the test articles. Based on the experimentally measured 3D shapes, several key parameters, such as full-field recession, dynamic recession rate, were calculated. The results demonstrate the efficacy and potential of UV stereo-DIC for 3D shape and recession measurements in ablation tests.
关键词： Recession,High temperature,UV stereo-digital image correlation,Ablation shape
更新于2025-09-23 15:22:29
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Displacement Measurement Errors in Digital Image Correlation Due to Displacement Mapping Function
摘要： In the classic subset-based local digital image correlation (DIC) technique, the displacement measurement errors due to the displacement mapping function have been an important factor to improve the measurement accuracy. In general, the first-order displacement mapping function is broadly used. But, in the real experiments, the order of the deformation of the test sample is higher than that of the used displacement mapping function. So the errors due to the undermatched displacement mapping functions are existent. Although the random errors due to the overmatched shape function have been studied, the root-mean square errors (RMSEs) due to the matched or mismatched displacement mapping function are not studied. In this paper, the RMSEs of the measured displacements due to the matched or mismatched displacement mapping function are investigated experimentally by employing the simulated and real experimental speckle patterns. Moreover, the relationships between the RMSE and the subset size or the image noise are thoroughly examined. Finally, the practical implementation of DIC is recommended in terms of the subset size and the image noise.
关键词： Shape function,Error,Digital image correlation,Undermatched,Displacement,Displacement mapping function
更新于2025-09-23 15:22:29
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Camera array-based digital image correlation for high-resolution strain measurement
摘要： Digital image correlation (DIC) is a well-known technique for non-contact, non-destructive, full-field deformation measurement in experimental solid mechanics. Although DIC has been widely used in science and engineering, the resolution of strain measurement with DIC is limited by imaging resolution and is much lower than that obtained with a strain gauge. To achieve a breakthrough in strain measurement using DIC, a camera array-based DIC method is proposed herein for high-resolution strain measurement. Twenty-five industrial cameras were assembled into a plane array, with each camera capturing a part of the specimen. A novel calibration-based image stitching method is proposed and was applied to these images and their corresponding displacement fields. The strain field was then calculated based on the stitched displacement fields. The use of the camera array greatly improved the measurement spatial resolution of DIC and made high-resolution strain measurement possible. Both static error analysis and four point-bending experiments were performed to demonstrate the feasibility and effectiveness of the proposed method, and a full-field strain resolution of 10 με was achieved.
关键词： displacement field stitching,camera array,Digital image correlation,image stitching,high-resolution strain measurement
更新于2025-09-23 15:21:01
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Measurement of Weld Zone Properties of Laser-Welded Tailor-Welded Blanks and Its Application to Deep Drawing
摘要： Weld zones in tailor welded blanks have different mechanical properties than the base metals and thus have significant effects on formability. In this work, flow stresses of weld zones in laser-welded dissimilar dual-phase steels were measured. Strains at the weld zones of notched specimens were measured using the digital image correlation method and the flow stress data were corrected considering the anisotropy. For validation, finite element simulations were performed for the cup drawing process by considering the measured weld zone properties, and the weld line movements were compared with the measurements.
关键词： Laser welding,Formability,Digital image correlation,Dual-phase steel,Flow stress
更新于2025-09-23 15:21:01
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Microcontact printing on metallic surfaces for optical deformation measurements
摘要： The measurement of the properties and behaviour of material is of fundamental importance in modern engineering. In recent years a breakthrough method for measuring surface deformation has been represented by digital image correlation. To determine local deformations in a material, an optical pattern is usually reproduced on the material surface. The reproduction of such patterns, especially at microscopic scale, is usually a slow and expensive procedure. A semi-automated device, able to print a suitable optical pattern on the metallic surface using micro-contact printing, was manufactured. Precision placing of the stamping head on the surface in order to avoid smearing of the pattern was reached. Specifically the stamp was placed with tolerances of some micrometres. Despite posing challenges in the handling of the ink and in the consistency of the patterns, this method proved viable for effective and fast creation of optical patterns.
关键词： microimprint,digital image correlation
更新于2025-09-23 15:21:01
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Evaluation of large plastic deformation for metals by a non-contacting technique using digital image correlation with laser speckles
摘要： The full-field deformation characterizations of a metal undergoing large plastic strains are difficult to be obtained from the conventional true stress-strain curves. In this study, we proposed using a simple non-contacting technique, digital image correlation (DIC) with laser speckles, to evaluate large plastic deformations of metals, especially for thin metal foils and for the forming at high temperatures. The feasibility and accuracy of this DIC technique were confirmed by conducting uniaxial tensile tests using different materials. As results, the measured strains indicated a good accuracy with an error range of 6% in measuring the large plastic deformation at room temperature and 10% in measuring a large strain up to 0.6 at a high temperature of 400 °C. The strain distribution measured by DIC with laser speckles and with artificial speckles showed good agreement, confirming the feasibility of this DIC technique for measuring large plastic deformations. By using this technique, the evolution of plastic zone was successfully investigated for thin metal sheets with a thickness of 0.5 mm. Furthermore, the strain fields involving localizations of 50 μm thick metal foils forming at room temperature and a large plastic deformation of metal tubes forming at 400 °C were evaluated qualitatively and quantitatively.
关键词： Large plastic deformation,Digital image correlation,Non-contacting,Laser speckle,Metal
更新于2025-09-23 15:21:01
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Mechanical response of a Laser Cladding repaired structure: localization of plastic strain due to microstructure gradient
摘要： Laser Cladding is an additive manufacturing technology enabling to repair complex metallic components by removing the worn region and reconstructing locally the initial geometry. The aim of this work is to study the mechanical response of Inconel 718 repaired thin walls. More precisely, we perform an EBSD imaging and in-situ SEM tensile tests on specimen whose gauge section contains the interface between base material and repaired area. We observe the multiaxial strain patterns until failure at the grain level using a Digital Image Correlation method and superpose this pattern with the microstructure gradient induced by repair. The observations highlight a strain localization phenomenon in repaired structures mainly due to grain size effect.
关键词： SEM tensile tests,Laser Cladding,Inconel 718,strain localization,EBSD,microstructure gradient,Digital Image Correlation
更新于2025-09-23 15:19:57
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Uniformity and isotropy of speckle pattern cause the doubled random error phenomenon in digital image correlation
摘要： For subset-based digital image correlation, the random error of second-order shape function roughly doubles that of first-order shape function, termed doubled random error phenomenon. In this work, we suggest that the fundamental cause of this phenomenon is the uniformity and isotropy of speckle pattern. Specially, we prove that the ratio of random error of second-order shape function to that of first-order shape function, from a view of statistic, is expected to be √7∕2 (≈1.87), which is quite close to the empirical value 2. Numerical experiments demonstrate the correctness of propose theoretical analysis.
关键词： Speckle pattern,Digital image correlation,Random error,Statistical analysis
更新于2025-09-23 15:19:57