Review of Development and Application of Digital Image Correlation Method for Study of Stress–Strain State of RC Structures

Abstract

Reliable assessment and prediction of the technical condition of reinforced concrete structures require accurate data of the stress–strain state of the structure at all stages of loading. The most appropriate technique to obtain such information is digital image correlation. Digital image correlation is a class of contactless methods which includes the following stages: obtaining an image from a studied physical object, saving it in digital form, and further analysis in order to obtain the necessary information about the stress–strain state of the structure. In this research, a detailed analysis of theoretical and experimental findings of digital image correlations was conducted. In the article, the main areas of scientific interest and computational approaches in digital image correlation issues were identified. Moreover, comparative analysis of alternative non-contact techniques, which also could be used for diagnostics of RC structures’ stress–strain state was conducted. The novelty of the study consists of a thorough comparative analysis with the indication of specific features of digital image correlation, which determine its wide application among the other similar methods. On the basis of the conducted literature review, it can be seen that the digital image correlation technique has gone through multi-stage evolution and transformation. Among the most widely studied issues are: image recognition and matching procedures, calibration methods and development of analytical concepts. The digital image correlation technique enables us to study cracking and fracture processes in structural elements, obtaining the full field of deformations and stresses. Further development of image processing methods would provide more precise measuring of stress–strain parameters and reliable assessment of structural behavior.

Digital Image Correlation for Assessment of Bridges’ Technical State and Remaining Resource

“…Digital Image Correlation (DIC) is a multi-stage technique which enables remote contactless measurement of full-field displacements and strains on the surface of objects. DIC has been widely used in various fields, including materials testing [2,7], structural analysis, biomechanics, and experimental mechanics, providing valuable insights into the mechanical behaviour of materials and structures. Although this method has experienced a long history of development [2] and modifications and could have specific features, which depend on the particular application field, it generally includes several key steps.…”

“…The basic principle of DIC image tracking entails the representation (coding) of it with a matrix of natural numbers (e.g., white areas corresponding to 0, while black, -to 100). Thus, the subset of the image (normally a square with a 10-50 pixels side) will contain the group of points with different grey level variations and unique numerical coding [2,8] (See Figure 2). The centre of a particular subset, as the reference point, serves for its further tracking through the subsequent "deformed" images and coordinates identification.…”

“…Throughout the correlation procedure, sets of numbers are systematically shifted until the pattern on the deformed image aligns optimally with the reference image. This alignment is determined by assessing the overall difference in grey levels for each corresponding point [2,8].…”

“…Thus, the choice between natural and artificial, or a combination of both patterns involves a trade-off between precision and ease of application, being an aspect of crucial importance for ensuring the accuracy of results [10], [11]. Thus, the artificial speckle pattern, which is a random arrangement of bright and dark spots on a surface, should align with the following requirements [2,10] Following the flowchart of the DIC process (Figure 1) ensuring the use of optimal speckle pattern, correlation can be performed with high accuracy and low noise level. Cross-correlation algorithms are used to find the best match for each subset in the deformed images.…”

Application of Digital Image Correlation to Evaluate Strain, Stiffness and Ductility of Full-Scale LVL Beams Strengthened by CFRP

“…Later, this method was developed into 3D-DIC methods through the use of multiple cameras. The history of the evolution of this method is presented in more detail in [ 32 ].…”