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Dai Fulong

Bio: Dai Fulong is an academic researcher from Tsinghua University. The author has contributed to research in topics: Interferometry & Grating. The author has an hindex of 8, co-authored 27 publications receiving 551 citations.

Papers
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Journal ArticleDOI
TL;DR: A detailed examination of the performances of each algorithm reveals that the iterative spatial domain cross-correlation algorithm (Newton–Raphson method) is more accurate, but much slower than other algorithms, and is recommended for use in these applications.
Abstract: Developments in digital image correlation in the last two decades have made it a popular and effective tool for full-field displacement and strain measurements in experimental mechanics In digital image correlation, the use of the sub-pixel registration algorithm is regarded as the key technique to improve accuracy Different types of sub-pixel registration algorithms have been developed However, little quantitative research has been carried out to compare their performances This paper investigates three types of the most commonly used sub-pixel displacement registration algorithms in terms of the registration accuracy and the computational efficiency using computer-simulated speckle images A detailed examination of the performances of each algorithm reveals that the iterative spatial domain cross-correlation algorithm (Newton–Raphson method) is more accurate, but much slower than other algorithms, and is recommended for use in these applications

477 citations

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TL;DR: In this article, the formation of moire fringes when a HREM (high resolution electron microscopy) image of crystal material is superimposed with a unidirectional grating is described.
Abstract: Nano-moire method presented in this paper is an experimental technique which allows direct measurement of nanoscopic mechanical parameters, such as displacement, strain and dislocation distribution. The basic idea is the formation of moire fringes when a HREM (high resolution electron microscopy) image of crystal material is superimposed with a unidirectional grating. Fourier filtering technique is used to increase the contrast of fringes and to multiple the fringes. This method has atom-size sensitivity and spatial resolution, and relatively large range. It provides a new experimental technique with very high sensitivity and spatial resolution for nanomechanics.

28 citations

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TL;DR: In this paper, the dynamic deformation of a pre-loaded LY12 aluminium tensile specimen under a thermal heating was studied using the moire interferometry method, and the results showed that it is feasible to use the method for measuring dynamic deformations under conditions of fast heating.

14 citations

Journal Article
Dai Fulong1
TL;DR: The basic principles and several sub-pixel displacement registration algorithms are introduced and the shortcomings and advantage of different algorithms are illustrated on the basis of a survey of recent researches.
Abstract: Development in digital image correlation in the last two decades has made it a popular and effective tool for full-field displacement and strain measurements in engineering in general, and experimental mechanics in particular. In DIC, the sub-pixel registration algorithm is regarded as a key measure to improve accuracy. This paper introduces the basic principles and several sub-pixel displacement registration algorithms. It also illustrates the shortcomings and advantage of different algorithms on the basis of a survey of recent researches. With the further improvement of the algorithm accuracy as well as the development of hardware, the future of this method is promising in terms of widespread applications.

12 citations

Journal ArticleDOI
TL;DR: In this paper, the theory of moire interferometry and incremental hole-drilling (MIIHD) is introduced for non-uniform residual stress measurement, and an experimental system including real-time measurement, automatic data processing and residual stresses calculation is established.
Abstract: Hole-drilling method is one of the most convenient methods for engineering residual stress measurement. Combined with moire interferometry to obtain the relaxed whole-field displacement data, hole-drilling technique can be used to solve non-uniform residual stress problems, both in-depth and in-plane. In this paper, the theory of moire interferometry and incremental hole-drilling (MIIHD) for non-uniform residual stress measurement is introduced. Three dimensional finite element model is constructed by ABAQUS to obtain the coefficients for the residual stress calculation. An experimental system including real-time measurement, automatic data processing and residual stresses calculation is established. Two applications for non-uniform in-depth residual stress of surface nanocrystalline material and non-uniform in-plane residual stress of friction stir welding are presented. Experimental results show that MIIHD is effective for both non-uniform in-depth and in-plane residual stress measurements.

11 citations


Cited by
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Journal ArticleDOI
TL;DR: In this article, a review of the 2D digital image correlation (2D DIC) technique for displacement field measurement and strain field estimation is presented, and detailed analyses of the measurement accuracy considering the influences of both experimental conditions and algorithm details are provided.
Abstract: As a practical and effective tool for quantitative in-plane deformation measurement of a planar object surface, two-dimensional digital image correlation (2D DIC) is now widely accepted and commonly used in the field of experimental mechanics. It directly provides full-field displacements to sub-pixel accuracy and full-field strains by comparing the digital images of a test object surface acquired before and after deformation. In this review, methodologies of the 2D DIC technique for displacement field measurement and strain field estimation are systematically reviewed and discussed. Detailed analyses of the measurement accuracy considering the influences of both experimental conditions and algorithm details are provided. Measures for achieving high accuracy deformation measurement using the 2D DIC technique are also recommended. Since microscale and nanoscale deformation measurement can easily be realized by combining the 2D DIC technique with high-spatial-resolution microscopes, the 2D DIC technique should find more applications in broad areas.

2,530 citations

Journal ArticleDOI
TL;DR: A theoretical model of the displacement measurement accuracy of DIC can be accurately predicted based on the variance of image noise and Sum of Square of Subset Intensity Gradients (SSSIG), which leads to a simple criterion for choosing an optimal subset size for the DIC analysis.
Abstract: Digital Image Correlation (DIC) has been established as a flexible and effective technique to measure the displacements on specimen surface by matching the reference subsets in the undeformed image with the target subsets in the deformed image. With the existing DIC techniques, the user must rely on experience and intuition to manually define the size of the reference subset, which is found to be critical to the accuracy of measured displacements. In this paper, the problem of subset size selection in the DIC technique is investigated. Based on the Sum of Squared Differences (SSD) correlation criterion as well as the assumption that the gray intensity gradients of image noise are much lower than that of speckle image, a theoretical model of the displacement measurement accuracy of DIC is derived. The theoretical model indicates that the displacement measurement accuracy of DIC can be accurately predicted based on the variance of image noise and Sum of Square of Subset Intensity Gradients (SSSIG). The model further leads to a simple criterion for choosing a proper subset size for the DIC analysis. Numerical experiments have been performed to validate the proposed concepts, and the calculated results show good agreements with the theoretical predictions.

486 citations

Journal ArticleDOI
TL;DR: In this article, a simple and easy-to-calculate yet effective global parameter, called mean intensity gradient, is proposed for quality assessment of the speckle patterns used in DIC.

408 citations

Journal ArticleDOI
TL;DR: In this article, the authors review the latest developments in the numerical analysis of friction stir welding processes, microstructures of friction-stir welded joints and the properties of friction spat welded structures.

397 citations