Digital Correlation Method Research Articles

Development of Digital Imagine Correlation (DIC) Method for Three-Dimensional Rugged Surface of Construction Material

Digital Image Correlation, DIC method is developed a low-cost digital image correlation coefficient method based on advanced digital cameras and high-speed computers. Traditionally, two or more cameras are widely applied for conducting 3-D monitoring. There are numerous parameters need to be accurately calibrated. Therefore, the results of 3-D accuracy are worse than that of 2-D accuracy. The feasibility of a single camera to collect image to analyze the three-dimensional rugged surface of material is proposed in this study. A three-dimensional facial mask-like human makeup test and plaster cast are used to test. The test results reveal that the coordinate error between these two photos of the three-dimensional facial mask-like human makeup test is only 0.002mm and the absolute displacement, rotate on z-axis, strain on z-axis and von Mises strain of analysis results are extremely close to the real surface plaster cast.

OS09-3-3 Research on the Speed of Stress Wave with Digital Correlation Method

OS09-3-3 Research on the Speed of Stress Wave with Digital Correlation Method

OS09F122 Research on the Speed of Stress Wave with Digital Correlation Method

OS09F122 Research on the Speed of Stress Wave with Digital Correlation Method

Precise strain measurement in complex materials using Digital Volumetric Correlation and time lapse micro-CT data

Digital volumetric correlation (DVC) method can be employed for evaluation of full-volume displacement and strain fields in deformed material with clearly recognizable microstructure. This microstructure can be defined by complex inner geometrical topography, as trabecular bone and metal foam have for instance, or/and by significant variations of chemical composition, as aluminum grainy alloys have for instance. Volumetric image data were acquired using time lapse X-ray micro-CT during gradually specimen loading. Tetrahedral FE mesh was generated describing related volumetric data. The displacement fields were measured in set of control points by DVC utilizing vertices of this tetrahedral FE mesh. The advantage of the approach is that the resulting strain can be directly compared with FE simulation of the experiment. Problems of accuracy, especially in evaluation of the strain field from the noisy measured displacements and problems of computational efficiency of the method are discussed.

Evaluation of strain field in microstructures using micro-CT and digital volume correlation

X-ray digital micro-tomography was employed for precise strain measurement which is essential for evaluation of the experiments with small samples of trabecular bone. X-ray Digital Volumetric Correlation (DVC) method was used to identify the three-dimensional strain field in loaded complex microstructure. DVC relies on tracking selected sample points within the three-dimensional image data throughout the sequence of captured projections. In this study an improved DVC method is applied for evaluation of the strain field in trabecular bone sample subjected to compressive loading. The deformed sample was tomographically scanned using micro-focus X-ray tube and the single-photon counting silicon pixel detector Medipix2.

Determination of the fracture energy of a composite by the method of digital speckle correlation

We have developed a computational-and-experimental procedure for evaluating the fracture energy of composite materials, which lies in the determination of surface displacements in a neighborhood of the tip of a stress concentrator under static tension by the method of digital speckle correlation. Using the known displacement distribution, we calculate strains in the prefracture zone as well as the opening and shear of crack lips for given loading force and measuring base. The static tensile stress-strain diagram, together with the established specimen strain, enables us to find stresses in the prefracture zone. Using these data, we find the fracture energy of the composite. We also present some results of investigations for a three-layer composite material based on an epoxy-phenol plastic reinforced chaotically with disperse particles.

Effect of Ductile Damage Evolution in Sheet Metal Forming: Experimental and Numerical Investigations

The numerical simulation based on the Finite Element Method (FEM) is widely used in academic institutes and in the industry. It is a useful tool to predict many phenomena present in the classical manufacturing forming processes such as necking, fracture, springback, buckling and wrinkling. But, the results of such numerical model depend strongly on the parameters of the constitutive behavior model. In the first part of this work, we focus on the traditional identification of the constitutive law using oriented tensile tests (0°, 45°, and 90° with respect to the rolling direction). A Digital Image Correlation (DIC) method is used in order to measure the displacements on the surface of the specimen and to analyze the necking evolution and the instability along the shear band. Therefore, bulge tests involving a number of die shapes (circular and elliptic) were developed. In a second step, a mixed numerical–experimental method is used for the identification of the plastic behavior of the stainless steel metal sheet. The initial parameters of the inverse identification were extracted from a uniaxial tensile test. The optimization procedure uses a combination of a Monte-Carlo and a Levenberg-Marquardt algorithm. In the second part of this work, according to some results obtained by SEM (Scaning Electron Microscopy) of the crack zones on the tensile specimens, a Gurson Tvergaard Needleman (GTN) ductile model of damage has been selected for the numerical simulations. This model was introduced in order to give informations concerning crack initiations during hydroforming. At the end of the paper, experimental and numerical comparisons of sheet metal forming applications are presented and validate the proposed approach.

2P218 デジタル画像相関法を用いた生きた細胞における細胞骨格の動態解析(細胞生物的課題(接着,運動,骨格,伝達,膜),第48回日本生物物理学会年会)

2P218 デジタル画像相関法を用いた生きた細胞における細胞骨格の動態解析(細胞生物的課題(接着,運動,骨格,伝達,膜),第48回日本生物物理学会年会)

Determination of residual strain by combining EBSD and DIC techniques

Electron Back-Scatter Diffraction (EBSD) can be applied to determine lattice defect and local strain distortion. The strain components were obtained with the help of the shifting of zone axis in Kikuchi patterns generated from EBSD. The displacement of zone axis in Kikuchi pattern was determined by using Digital Image Correlation (DIC) method, which provides a great resolution down to 0.01 pixels, which means the ideal sensitivity to be ∼3.6 × 10−5. However, the errors of calculating the residual strain can result from the image quality of Kikuchi patterns, such as the formation of dark areas in the Kikuchi patterns and the background noise.

WITHDRAWN: Application of Digital Volume Correlation Method to Cell Traction Force Measurement

This article has been withdrawn at the request of the authors. The Publisher apologizes for any inconvenience this may cause. The full Elsevier Policy on Article Withdrawal can be found at http://www.elsevier.com/locate/withdrawalpolicy.

OS1104 走査型プローブ顕微鏡による形状解析データを用いたデジタル相関法(実験力学における最近の進歩,オーガナイズドセッション)

This paper describes the digital correlation method using the surface configuration data by the scanning probe microscope. The bending test is carried out on the table of the scanning probe microscope, and the configuration data on the specimen surface is obtained by the configuration analysis. After that, the estimation of the displacement field is carried out using the digital correlation method using the surface configuration data. In this paper, the accuracy of the estimation for the displacement field is investigated.

Surface profile measurement of moving objects by using an improved π phase-shifting Fourier transform profilometry

The π phase-shifting Fourier transform technique is introduced into the surface profile measurement of moving objects. A digital grating comprising two regions, which have a π phase shifting is projected onto the object. Two line-scan CCD cameras are used to capture two deformed fringe patterns with π phase shifting at the same time. As the object is moving, each point at the object surface can be captured twice. The digital correlation method is used to calibrate the experimental system. The zero-order component can be eliminated by subtracting intensities of the same surface point in two captured images. And then the phase can be extracted by Fourier transform without the disturbance of zero-order component. Experimental results demonstrate that this method is feasible for the moving surface profile detection and the measurable slope of height variation can be extended.

Methods and applications of digital volume correlation

Digital volume correlation, an experimental method for volumetric strain measurement, has experienced a growth in technique development and application since its introduction in 1999. This has largely been the result of more accessible volumetric imaging methods and greater speed and capacity of computational facilities. This paper reviews recent work using the method and presents examples from the author's laboratory. The emerging message is that, although closely related to the surface-oriented method of digital image correlation, the volume method is distinct due to its predominant reliance on naturally occurring image texture for displacement tracking. This requires careful tuning for successful application with different materials, and therefore the appropriate focus should not be on developing the ‘best’ digital volume correlation method, but on developing a set of tools that can be selected from and adjusted to specific mechanics problems.

A subpixel motion estimation algorithm based on digital correlation for illumination variant and noise image sequences

One of the challenges in practical subpixel motion estimation is how to obtain high accuracy with sufficient robustness to both illumination variations and additive noise. Motivated by the fact that the normalized spatial cross-correlation is invariant to illumination, we introduce a gradient-based subpixel registration method by maximizing the digital correlation (DC) function between the reference and target frames. Such DC function is remodeled with the presence of image noise, yielding that the correlation coefficient is only sensitive to noise standard variance. To fairly suppress the noise corruption, not only the target frame but also the reference one is reformulated into Taylor gradient expression with half but opposite motion vector. The final solution to motion estimates can be approximated into a closed form by reserving first-order coefficient terms of unregistered motion variables. The error trend of approximated solution is discussed. Computer simulations and actual experiments’ results demonstrate the superiority of the proposed method to the LMSE-based method and ordinary DC method when illumination variations and noise exist. Among the experiments, the influences of real subpixel translation value and noise variance degree on accuracy are studied; correspondingly, an optimized iterative idea for big translations and the recommended noise level adaptive to our method are introduced.

Experimental study on the surface stress measurement with Rayleigh wave detection technique

In this paper, experimental study on the surface stress measurement of a metallic material based on the Rayleigh wave acoustoelastic theory is introduced. A Rayleigh wave acoustoelastic formula deduced by Husson is optimized to estimate the surface stress of the material. Two micro Rayleigh wave transducers with 5 MHz frequency one of which is used for acoustic pulse emitter and another for receiver are used to determine the time of flight of Rayleigh wave propagating in a certain distance along the surface of the material. The difference in time of flight between two ultrasonic signals obtained in stressed and unstressed object surface is identified by the digital correlation method. A specimen made of Q235 steel and applied with tensile load is used for calibration to obtain the acoustoelastic coefficients of Q235 steel. Furthermore, some principal factors which may result in errors in the experiment are discussed and some measurements are proposed to prevent these errors. Finally the surface stress of a cantilever beam is detected by the Rayleigh wave acoustoelastic technique and the experimental result is well compared with the theoretical value.

Comparison of the Tensile Performance of Polymer PC and PC/ABS

Large deformation performances of polycarbonate (PC) and PC/ABS (Acrylonitrile Butadiene Styrene) have been investigated experimentally in this paper. The displacement fields of these polymers are measured with a system based on digital image correlation (DIC) method. The variations of strains during tension are measured and the true stress-strain curves are presented. For these materials, it is observed that the contraction in thickness is larger than that in width during tension. No obvious stress softening is observed in the true stress-strain curves. The true stress-strain curves can be fitted well with three-stage model.

Application of Stress Analysis by Digital Image Correlation and Intelligent Hybrid Method to Unidirectional CFRP Laminate

Fiber reinforced composites are heterogeneous and anisotropic. The applicability of the stress analysis methods on such heterogeneous and anisotropic materials is not well known. In the present study, an attempt is made to apply the digital image correlation method and the intelligent hybrid method to a carbon fiber reinforced plastic (CFRP) laminate. A material used is carbon/epoxy system. Laminate configuration is unidirectional. Tensile load is applied in off-axis (45 degrees) direction as well as longitudinal (0 degree) and transverse (90 degrees) directions on a CFRP laminate. Displacement, strain and stress fields due to the tensile loading in the CFRP unidirectional laminate are analyzed. The constitutive equation considering material anisotropy is built into the intelligent hybrid method used at the time of analyses. The validity of the algorithm is checked through comparison between results of the present method, experimental results from strain gauge method, and the analytical results from finite element method (FEM).

Evaluation of the surface strains in the composites by the methods of digital speckle correlation

We study the surface strains formed in composite materials under the conditions of static loading by a modified method of digital speckle correlation. For this purpose, we analyze polymeric composite materials chaotically reinforced with short glass fibers. The strain fields formed near the notches made in the specimens are constructed.

Applications of Digital Correlation Method to Structure Inspection

In structure inspections, applications of optical techniques are rare, but the advantages of a non-contact, full field technique using a simple apparatus are attractive. The main requirements for structure inspection are the full-field strain measurement with the required precision and on-site measurement ability. The digital correlation method (DCM), a new optical deformation measurement tool, can satisfy all of the requirements for structure inspection. A smoothing algorithm which can greatly improve the strain measurement precision, and a 3-D DCM have been developed in this paper. For verifying this improvement, a comparison of strain measurements by computer-simulated speckle images has been carried out. Additionally, three structure inspection examples that cover typical materials and structure styles are presented: the interface shear stress distribution for reinforced concrete piles bedded on rock, the 3-D strain distribution of a composite vessel structure, and stresses in a hookup that connects two steel bridge structures. All the examples show that the new structural inspection tool is exemplary and illustrates the obvious advantages of this optical non-destructive technique.

Experimental Study of Micro Displacement Field of Microstate of Crack Tips of Ceramics Plasticized with Zirconia and Stabilized by Yttrium Oxide – Application of Digital Image Correlation Method Based on Analysis by Scanning Electron Microscope

To study the deformation reaction of different metallurgical phases of the micron structure of crack tips of zirconia ceramics in the loading state, the paper presents the micro experimental study based on the digital correlated method of analysis by scanning electron microscope on the displacement field in the micro areas of crack tip of the specimen of the Y2O3-ZrO2 toughened ceramic with the simple edge notch beam method and under the action of three-point bending loads. First, SEM analyses was made on the local area of the crack tip of a specimen’s polished surface before and after loads are applied to the specimen, thus obtaining two SEM images, one before the application of the loads and another after the load application, which contained their displacement information. Then, digital correlation calculations were made between the gray scales of the pixels of the two images in order to obtain the microscopic displacement fields of the crack tips in the microstate, thus unveiling the deformation modality and displacement response of different metallurgical phases of the crack tips of zirconia ceramics when subject to loads. The results of the studies will provide foundations and basis for further research in the mechanical properties of the ceramics with Y2O3-ZrO2 and their relationship with the microstructures.