Publication: Computational digital image correlation approaches for structural monitoring applications
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Date
2023-09-01
Authors
Mohammed Abbas Mousa
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Abstract
A picture is worth not only a thousand words, but it can be worth a thousand sensors! The Digital Image Correlation (DIC) technique is an optical, full-field, and non-contact method that employs digital images to measure the two- or three-dimensional components of motion or deformation. The technique is used in many fields, such as solid mechanics, material and structural tests, biology, and others. However, the DIC is prone to errors and limitations that hinder its use in structural tests and applications. These errors and limitations arise from the optical nature of the technique and the complex setup of the tested structural elements. The errors generated from external and internal sources include camera and specimen movement, poor speckle patterns, and random image noise. Therefore, several computational approaches have been applied to 2D-DIC in the literature, like image pre-processing and post-processing of the DIC data. These approaches were assessed through three laboratory experiments of glass and concrete elements and two field tests of concrete structures involving shear wall and bridge pier. The out-of-plane deflection results of the glass sheet are within a 7% difference between the dial gauge and 2D-DIC readings. Similarly, the shear-wall experiment showed that the strain gauge values were within a 7% difference from the in-plane strain data provided by 2D-DIC. Then, it is demonstrated that the Pixel Average (PA) approach enhanced the accuracy of the 2D-DIC data by reducing the variations (S2) of the concrete arches differential strain Diff(εx) up to 90%. Also, the coefficient (R2) improved from 0.45 to 0.9 when ten to twenty averaged images were used. Also, the Image Erode (IE) yielded improved speckle quality with a uniformly high surface component. The concrete arches bending test results show that the crack location was automatically detected and measured. Also, the probability of the cracked section shows a higher possibility of cracking (57% - 76%) respectively at (25% - 50%) of the cracking load compared to (8% - 60%) possibility of cracking of the uncracked sections at the same loading range. Finally, the long-term monitoring of crack width expansion in the bridge pier is almost (0.01mm) when the temperature rises (6 °C). In addition, the crack measurement from the DIC and the demec gauges were compared, and equivalent crack expansion values were found to be (0.004 -0.005)mm for both the DIC and the demec measurements. The results of the experiments show that the 2D-DIC, with the help of computational approaches, can be a reliable monitoring tool.