Issue 78

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

Figure 11: SEM micrographs of fractured surfaces of Si ₃ N ₄ -modified H/B F-Ep composites after fracture toughness testing: (a, b) S1, (c, d) S2, (e, f) S3 and (g. h) S4 at low and high magnifications. The treated composite (S0t; Fig. 10c, d) exhibits stronger fiber–matrix contact, more fragmented fibers, better fiber encapsulation, and less fiber pull-out than S0u. Due to increased basalt–epoxy interaction after silane treatment and improved hemp surface roughness after alkali treatment, the rougher fracture surface denotes increased crack tortuosity and energy dissipation. These changes reduce early interfacial debonding and enhance stress transmission [41]. The S1 composite (0.5 wt. % Si ₃ N ₄ ; Fig. 11a, b) shows enhanced fiber encapsulation, reduced fiber pull-out, and localized matrix cracking. Increased fracture energy and KIC are the results of well-dispersed nanoparticles strengthening the interphase and encouraging crack deflection. Ceramic nanoparticle-reinforced natural fiber composites have shown comparable toughening effects [36]. Additionally, after homogenous nanoparticle dispersion in fiber/epoxy composites, Chandra et al. [37] showed enhanced interfacial adhesion and crack resistance. The best fracture morphology and maximum K IC were shown by S2 (1 wt. % Si ₃ N ₄ ; Fig. 11c, d). Effects of stress transfer and energy dissipation are indicated by limited fiber pull-out, significant fiber fracture, cohesive matrix tearing, and a rough fracture surface. The increased fracture resistance is a result of a combination of crack deflection, pinning, branching, fiber bridging, and matrix tearing [38, 40].

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