Issue 78

R. Shivashankar et alii, Fracture and Structural Integrity, 78 (2026) 454-473; DOI: 10.3221/IGF-ESIS.78.26

Figure 5: SEM micrographs of flexural test failed untreated H/B F-Ep composites: (a) Hemp fabric region, (b) Basalt fabric region

Figure 6: SEM micrographs of flexural test failed treated H/B F-Ep composites: (a) Hemp fabric region, (b) Basalt fabric region After adding 0.5 wt. % Si ₃ N ₄ , the fracture morphology of S1 (Fig. 7a and 7b) shows enhanced interfacial performance. Stronger fiber–matrix adhesion than S0t is shown by fewer matrix cracks, better fiber encapsulation, shorter fiber pull-out, and fewer interfacial voids. In addition to pinning and deflecting cracks locally, well-dispersed Si ₃ N ₄ nanoparticles strengthen the matrix and interphase. Higher flexural strength (232.78 MPa) and modulus (11.03 GPa) with a maximum deflection of 7.2 mm are the results of these effects, which also enhance stress transmission and fracture resistance. Figs. 7(c–d) show the fracture morphology of S2 (1 wt.% Si ₃ N ₄ ), which exhibits improved fiber–matrix adhesion compared with S1. Greater fiber encapsulation, fewer interfacial voids, and reduced fiber pull-out indicate enhanced stress transfer. The relatively rough fracture surface and localized matrix deformation suggest crack pinning and deflection by well dispersed Si ₃ N ₄ nanoparticles. Consequently, S2 achieved higher flexural strength (244.62 MPa) and modulus (11.64 GPa). Figs. 7(e–f) show S3 (1.5 wt.% Si ₃ N ₄ ), which exhibited the most compact fracture morphology, strong fiber–matrix bonding, minimal voids, and limited fiber pull-out. The relatively tortuous fracture surface indicates effective crack deflection and energy dissipation. These features correspond to the highest flexural strength (258.91 MPa) and modulus (12.48 GPa), confirming 1.5 wt.% Si ₃ N ₄ as the optimum loading. In contrast, S4 (Figs. 7g–h) shows localized Si ₃ N ₄ agglomerates and matrix-rich regions. These clusters can act as stress concentration sites and promote crack initiation, reducing the effectiveness of stress transfer and crack deflection. Accordingly, flexural strength and modulus decreased to 248.17 MPa and 11.82 GPa, respectively, while maximum deflection decreased to 6.5 mm. Overall, the SEM observations support the mechanical results. Fiber surface treatment improved interfacial bonding, while well-dispersed Si ₃ N ₄ enhanced crack pinning, deflection, and stress transfer. S3 provided the best balance between nanoparticle dispersion, interfacial reinforcement, and crack resistance, whereas excessive loading in S4 promoted agglomeration and slightly reduced flexural performance.

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