PSI - Issue 66

Sneha et al. / Procedia Structural Integrity 66 (2024) 419–425 Author name / Structural Integrity Procedia 00 (2025) 000–000

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3. Results and discussion The compressive strength has been examined at 28 days of casting. The average compressive strength of 126 MPa has been reported from compressive testing. The results from the fracture testing with a load-CMOD curve for all three cases have been shown in Figure 3. This clearly represents that fibre variation has a significant effect on peak load as well as post-cracking profile. The flexural strength of notched specimens for 2 %, 2 % and hybrid, and 1.5 % has been reported as 15.57 MPa, 13.32 MPa, and 10.91 MPa. The fracture energy for all three has been depicted in Figure 4. Both the flexural strength and fracture energy got enhanced with 2% fibres which shows fracture mechanics is highly influenced by the fibre content and fibre length. Due to the higher fibre volume, the tensile strength of the material increases, allowing it to endure greater stress before failure. Additionally, the increased fibre content enhances the crack bridging mechanism, as more fibres are available to engage in resisting crack propagation, thereby providing maximum resistance to crack growth. Alongside the analysis of DIC results through crack propagation in terms of crack length and crack width the mechanism of crack propagation will be clearly understood. During the loading process, specimen deformation evolves with the applied load, while the fracture process zone (FPZ) continuously expands throughout the fracture development [12]. In order to observe the appearance and propagation of FPZ, the pre-MOR and post-MOR are divided into segments or points, as detailed in the previous section. The results on these different points has been shown in Figure 5. It is interesting to note that even though a 2 % fibre volume fraction has more peak load. The hybrid combination of fibres is performing better in terms of crack propagation till failure. The results of the same are shown in Figure 5. The main reason for this behaviour is that hybrid fibre with 13 mm and 20 mm fibres offers a dual fibre bridging mechanism. The short fibres contribute to suppressing the micro-cracks, whereas longer fibres activate when macro-cracking starts. This will limit the initiation and growth of small cracks, and a dense distribution of barriers leads to slow crack propagation. The short crack delays the coalescence of microcracks into the macro crack and leads to reducing the crack opening length. On the other hand, with no hybridization, longer fibres engage later, leading to large crack lengths and wide openings of cracks in the initial stage itself. In short, they are effective at large crack sizes but have less control over early crack growth. The above-stated results follow the same trend as those stated in existing literature (9,13).

Figure 3. Load-CMOD response of all three sets.