PSI - Issue 64

Amrita Milling et al. / Procedia Structural Integrity 64 (2024) 1009–1016 Milling/ Structural Integrity Procedia 00 (2024) 000 – 000

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(A BTRM = 25mm x 8mm) (ACI Committee 434 2011). Strain values were obtained from the displacement extracted using the DIC technique and the virtual gauge lengths. Toughness, a measure of the energy absorption capacity of the BTRM composite, was calculated as the area under the stress-strain plots up to the point of fracture. BTRM composites tested in the quasi-static range, 0.005 < ̇ ≤ 0.01/ , and in the dynamic range, 0.5 < ̇ ≤ 10/ , displayed tri-linear and bi-linear behaviours, respectively. The various regions are distinguished by the slope of the tangent modulus, shown by the dotted red lines in Fig.3.

Fig.2.Stress-strain response (a) 0.005 < ̇ ≤ 0.01/ (b) 0.5 < ̇ ≤ 1/ (c) ̇ ≈ 2/ (d) 6 < ̇ ≤ 10/ Table 3 presents the mean tangent moduli of Stages I, II, and III at different strain rates. Stage I, which corresponded to uncracked behaviour, consistently had the highest moduli. Compared to quasi-static tests, the shift to dynamic conditions resulted in a more than 40% rise in the average slopes (stiffness) of the first stages. Stage II was characterized by the initiation and propagation of microcracks within the matrix. The stress-strain relationship became linear again but with a lower stiffness compared to the initial stage. The point of transition between Stages I and II (first cracking stress) occurred in the range of 517 and 1405 MPa. For the quasi-static specimens, Stage II was a region of crack development, as expected from existing literature (D'Anna et al. 2021; Ghiassi 2019). For the dynamic specimens, however, it was not possible to distinguish between the crack development and crack opening stages; therefore, Stage II included both until the point of failure. Significant stress drops in Stage II corresponded with the development of new cracks. For instance, Points A, B, C, and D (Fig.3), which are located after the drops in Stage II, correspond with the four crack openings. Stage III for the 'QS' specimens began after the micro-cracks were formed, and a regain in stiffness was observed. In this stage and Stage II of the dynamic bilinear curves, the behaviour was governed primarily by the mechanical properties of the grid. The final stage of all the stress-strain curves was characterised by crack width opening until the basalt grid had reached its ultimate capacity and ruptured.