PSI - Issue 66

Ram Lal Riyar et al. / Procedia Structural Integrity 66 (2024) 181–194 Ram Lal Riyar et. al./ Structural Integrity Procedia 00 (2025) 000–000

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propagation at different stages and sizes. The popular damage detection method described here is non-contact measurement with DIC. 2.3. Digital Image Correlation Technique (DIC) The displacement information of a specimen surface may be determined using the advanced optical method known as DIC. Many researchers have utilized this method to monitor the emergence and crack progress in concrete material. Since it allows for close monitoring in real-time and precise synchronization, it is often used to evaluate materials' mechanical properties, as mentioned by Lian et al. (2022). Furthermore, DIC allows for the accurate imaging of crack growth in concretes subjected to testing and observing changes in damage rates developed in different materials. It is a reliable approach to see, measure, and interpret the surface discontinuities or deformations in material under a certain load. This method was given by Sutton et al. (1983), created in the latter decades of the 20th century, and is continuously modified to meet specific requirements. The technique has transformed stereo-photogrammetry, a method that uses sophisticated computer systems to effectively manage and analyze the extensive data sets resulting from experimental endeavors. Li et al. (2020) used DIC technology to examine how fully graded concrete dams formed their fracture process zone at different loading rates. The results show that dam concrete's FPZ development exhibits progressive growth characteristics. Before peak load, the FPZ began to develop, and soon after peak load, the fast expansion was almost complete. Including particles of significant size can enhance the fracture toughness and energy of concrete by creating divergences and meandering within the zone of the fracture process. The DIC method was applied by Wu et al. (2011) to examine the FPZ length of a three-point bending beam for a range of span-to-height ratios. The propagating length was shown to increase gradually as the crack spread but to diminish after the fracture process zone had completely formed. It was shown that when specimen height is increased while maintaining a fixed notch depth, the FPZ length at maximum load rises, but reduction occurs when the ratio between the depth of the notch and the height of the specimen is increased mentioned by riyar et al. (2023) Various DIC-based methods for determining the length of the FPZ are available in the literature given by Otsuka et al. (2000), Le et al. (2014), and Dong et al. (2017). Here a gradient-based methodology given by Bhowmik and Ray (2019) is used for estimating the FPZ length. Based on this approach, the effective crack or FPZ peak following the gradient in the horizontal displacement tends to be minimal or zero. During the DIC analysis, the initial notch's peak was marked as the origin. Through DIC analysis, corresponding horizontal displacement fields are obtained. Moreover, the calculation of displacement gradient is performed regarding each reference line. The reference line that exhibits a small displacement gradient indicates the location of the FPZ's tip. 3. Results and Disscussion The current experimental study attempts to comprehend the behavior of 6, 8, and 10 mm reinforced bars with various beam dimensions and longitudinal reinforcement percentage variations. The experimental data collected during the testing phase, comprising the load, vertical displacement at the mid-span, and CMOD were analysed. The plot illustrating the relationship between Load and CMOD, as derived from the experimental analysis of a lightly RC beam, is shown in Figure 3. Beams with different reinforcement ratios exhibit similar behviour as they nearly coincide at the early stages of loading. Later the linear stiffness and peak load of reinforced concrete beams increased as the percentage of reinforcement increased. When the load reached its peak, the reinforcing bar continued to elongate until it finally failed. In the 10 mm diameter bar the elongation is more than 8 mm and 6 mm bars. A size effect study has been performed to determine the non-linear fracture properties of concrete. The maximum loads for 6 mm, 8 mm, and 10 mm bars in small, medium, and large beams have been determined, and the resulting load values and related CMOD have been presented for the three different beam sizes. The regression analysis has been carried out to perform the size effect analysis using the maximum load values. The parameters such as structural size (D), and notch to depth ratio (a0/D) and ft are used to calculate the unknown coefficients C and A in the size effect law [ 1]. The coefficients Bf and D0 have been calculated through regression analysis.