Issue 78

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

Figure 7: SEM micrographs of flexural test failed Si3N4-modified H/B F-Ep nanocomposites: (a, b) S1, (c, d) S2, (e, f) S3, (g, h) S4 EFFECT SI 3 N ₄ CONTENT ON FRACTURE TOUGHNESS OF H / B F - EP HYBRID COMPOSITES ig. 8 shows the fracture toughness results of hemp/basalt–epoxy (H/B F-Ep) hybrid nanocomposites that were untreated, treated, and filled with nano-Si ₃ N ₄ . The fracture toughness of the untreated composite (S0 ut ) was 1.7054 MPa. √ m. The fibers' fracture toughness improved to 1.8586 MPa. √ m after alkali treatment (S0 t ), which is about 9.0% better than S0 ut . Improved fiber surface cleanliness and higher fiber–matrix interfacial adhesion, which encouraged more efficient stress transfer during fracture propagation, are responsible for this improvement. The inclusion of Si ₃ N ₄ nanoparticles improved the composites' resistance to fracture. Fracture toughness increased to 2.3298 MPa. √ m, 2.6828 MPa. √ m, 2.6002 MPa. √ m, and 2.4359 MPa. √ mfor S1 (0.5 wt% Si ₃ N ₄ ), S2 (1 wt% Si ₃ N ₄ ), S3 (1.5 wt% Si ₃ N ₄ ), and S4 (2 wt% Si ₃ N ₄ ). The percentage gains were roughly 36.6%, 57.3%, 52.5%, and 42.8% in comparison to the untreated composite (S0 ut ). S2 had the highest fracture toughness of all the compositions, suggesting that the ideal nanoparticle loading for optimizing crack-growth resistance was 1 wt. % Si ₃ N ₄ . F

Figure 8: Fracture toughness of Si 3 N 4 filled H/B F-Ep hybrid nanocomposites. The combined effects of Si 3 N ₄ nanoparticle reinforcement and fiber surface modification are responsible for the increase in fracture toughness. Hemp fibers' surface contaminants are eliminated by alkali treatment, which increases surface roughness and enhances fiber–matrix interaction and stress transfer. Through crack deflection, pinning, branching, particle debonding, crack-tip shielding, and localized matrix deformation, the addition of Si ₃ N ₄ further improves fracture resistance. Energy dissipation and crack-path tortuosity are increased by these mechanisms. The highest fracture toughness was shown by S2 (1 wt. % Si ₃ N ₄ ), suggesting an ideal compromise between nanoparticle dispersion, particle–matrix interaction, and crack-arresting effectiveness. Nanoparticle agglomeration, which can produce

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