PSI - Issue 66

Vivek Vishwakarma et al. / Procedia Structural Integrity 66 (2024) 381–387 Author name / Structural Integrity Procedia 00 (2025) 000–000

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days. Additionally, a 3 mm wide notch with a length of 30 mm was saw-cut on the 28 th day of curing. The reinforcement ratio was designed in accordance with the criteria given by Bosco & Carpinteri, (2018). 2.2. Experimental procedure The beam specimens were tested under centre point loading with constant amplitude cyclic loads at varying load ratios. All tests were conducted using a 500 kN closed-loop servo-controlled fatigue testing machine. The typical geometry of the beam is depicted in Figure 1. The crack mouth opening displacement was measured using a clip gauge. Initially, the beam specimens were tested under CMOD-controlled monotonic load to determine their static load capacity. Subsequently, the beam specimens were tested under constant amplitude cyclic load with stress ratios (R) 0.6 and 0.7. The loading frequency was maintained at 2 Hz for all the tests. To ensure proper contact, the minimum load was set at 2 kN . The tests were monitored continuously by an AE monitoring setup equipped with six R-15I-UC sensors to record AE waves.

Figure 1 Geometrical details of the lightly reinforced beam.

The acquisition threshold is kept at 45 dB, and a frequency band of 5 kHz to 600 kHz is used. Ensemble wave velocity is kept at 34000 m/sec . Surface displacement and strain measurements were obtained using a 2D-DIC setup. Davis software by LaVision was used to analyze the DIC images. Root mean square error (RMSE) is calculated by conducting a repetitive pencil break test on the known locations of the beam specimen to estimate the localization accuracy. These RMSE values were used as spatial bin size in the latter part of the study.

3. Results and Discussion 3.1. Mechanical behaviour

The single-edge notched, lightly reinforced concrete beam, under monotonic loading, exhibited a bi-linear load CMOD response, as shown in Figure 2. The first linear zone extended to a CMOD of 0.05 mm, followed by a brief

period of constant load until 0.2 mm CMOD. The second linear zone continued to CMOD of 1 mm , The slope change in the loading curve marks the instance of crack initiation from the notch and crossing the reinforcement. A dominant Figure 2. Load vs CMOD response of the lightly reinforced beam