International Research Journal of Engineering and Technology (IRJET)
e-ISSN: 2395-0056
Volume: 09 Issue: 05 | May 2022
p-ISSN: 2395-0072
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A Review on Deformation Measurement from Speckle Patterns using Digital Image Correlation Haleema S. H. 1, Dr. Naveen S. 2, Dr. Deepambika V. A. 3 1PG
Student, Dept. of Electronics & Communication Engineering, LBSITW, Kerala, India Professor, Dept. of Electronics & Communication Engineering, LBSITW, Kerala, India 3Assistant Professor, Dept. of Electronics & Communication Engineering, LBSITW, Kerala, India ---------------------------------------------------------------------***--------------------------------------------------------------------2Assistant
Abstract - The deformation measurement of a structural
techniques it allow a vast area of structures to be measured efficiently from a distance and the DIC has gained increased favour in large-scale structural testing in recent years.
element subjected to external loads at any point is vital in several engineering domains such as mechanical, civil, aerospace, etc. For example, in the fields of mechanical engineering and civil engineering, the deformation properties are evaluated by measuring the surface displacement under a given load and structural stability is assessed by measuring the whole deformation of concrete and steel structures under load respectively. The conventional instruments that measure strain such as strain gauges, extensometers, etc. cannot create strain maps. A full-field strain measurement is possible with digital image correlation (DIC), a non-contact optical deformation measurement technology. The DIC method's main premise is to collect speckle images that are naturally carried or purposefully created on an object's surface before and after deformation and convert them into a gray image. This measurement method is easy to use, belongs to the noncontact measurement category, and has a high level of accuracy.
Three-dimensional (3D) DIC works by computing a correlation function between two gray-scale images taken at distinct time intervals before and after deformation. From the coordinates of captured images and the camera calibration process, the true spatial coordinates of locations before and after deformation are rebuilt. High spatial resolution charge-coupled device (CCD) or complementary metal oxide semiconductor (CMOS) cameras, camera tripod supports, optical lenses, lighting system, camera synchronization unit, speckle pattern, and computer with appropriate software for displaying post-processing and storing data are needed for 3D-DIC measurements.
2. REVIEW OF RELATED WORKS The method of implementing digital image correlation was first described in 1983 by Sutton et al. [1]. The authors describe how digital images of an object are taken before and after being transformed and use generated light intensity levels to transform distinct data into a continuous form through a surface fit.
Key Words: Digital image correlation, speckle images, deformation measurement
1. INTRODUCTION The determination of mechanical characteristics in various materials necessitates the use of appropriate strain measuring techniques. This is particularly true when loading circumstances result in complex heterogeneous deformation fields. Full field measurement techniques, in particular the Digital Image Correlation (DIC) methodology, are well suited to this task. This technique, also known as the white light speckle technique, is an optical-numerical full-field measuring technique that uses a comparison of images taken with a digital Charge Coupled Device (CCD) camera at different load steps to determine in-plane displacement fields at the surface of objects under any kind of loading. The primary concept of the DIC method is to collect speckle images on an object's surface that are naturally transported or purposely formed before and after deformation and convert them into a grayscale image.
To increase the accuracy of the DIC method, Bruck et al. [2] introduced the Newton-Raphson method of partial differential corrections and it is used to increase the accuracy of displacement and gradient calculations. The Newton-Raphson method is based on the calculation of correction terms that improve the initial assumptions of the DIC algorithm. By using the displacement of a subset center calculated within a pixel, the algorithm is less likely to find a local minimum, and more likely to find an absolute minimum. D. Lecompte et al. [3] compare three different speckle patterns that originate from the same reference speckle pattern and introduces a method for determining the speckle size distribution of speckle patterns using morphology. The results shows that the size of the speckle along with the size of the pixel subset used, clearly affects the accuracy of the measured displacements.
The DIC has been widely used in material testing where the specimen size is small and the experimental setup is wellknown. Due to its benefit over point-wise measurement
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