Issue 74

V. J. Kalyani et alii, Frattura ed Integrità Strutturale, 74 (2025) 89-114; DOI: 10.3221/IGF-ESIS.74.07

(d) (f) Figure 5: Dimension and procedure for preparation and strengthening of dumbbell shaped specimen for bond test Experimental test setup A 400 kN capacity Universal Testing Machine (UTM) is used to perform tensile tests on the coupon specimens. The UTM is regularly calibrated to ensure measurement accuracy. The placement of the coupon specimen between the upper and lower crossheads of the UTM, as part of the tensile test setup, is shown in Fig. 6. All tensile tests are conducted in accordance with ASTM D3039 [25] under ambient temperature conditions, at a constant displacement rate of 1-2 mm/s. The UTM is equipped with a calibrated load cell that records the applied force digitally through a data acquisition system. Load and displacement data are displayed in real time on a digital meter and recorded simultaneously. A video recording stand is used to document the failure behavior of the specimens during testing, and the footage is utilized to assist in the analysis of failure mechanisms. (e)

Figure 6: Test setup for tensile test on coupon specimens

After 7 days of ambient curing, the dumbbell specimens are subjected to monotonic loading using a universal testing machine (UTM), as shown in Fig. 7. The compressive load from the UTM is transferred as a direct axial tensile force to the dumbbell specimen through a specially designed and indigenously developed frame assembly. The load is applied at a constant displacement rate of 1-2 mm/min. A 100 kN compression type load cell, mounted at the top of the frame assembly, records the applied load. Displacement is measured using two Linear Variable Differential Transformers (LVDTs) mounted symmetrically on either side of the specimen. Additionally, a 5 mm gauge length electrical resistance strain gauge is installed at the center of the strengthened surface along the longitudinal axis to capture strain readings under tensile loading. Real time data of load, displacement, and strain are recorded using a digital data acquisition system.

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