Issue 78

R. Shivashankar et alii, Fracture and Structural Integrity, 78 (2026) 454-473; DOI: 10.3221/IGF-ESIS.78.26 The composite prepared in the present work, which consisted of alkali-treated hemp, silane-treated basalt and Si ₃ N ₄ (1.5 wt.%) exhibited maximum flexural strength (258.91 MPa) and flexural modulus (12.48 GPa). The small decrease seen in the case of S4 (2 wt % Si ₃ N ₄ ) suggests that the optimum concentration of nanoparticles was surpassed during the present processing conditions. This behavior is consistent with the previous studies that revealed that high content of nanoparticles leads to agglomeration and poor mechanical properties [34].

Relevance to present study Optimum multiscale reinforcement Confirms nanoparticle induced flexural enhancement Supports interfacial strengthening by nanoparticle/silane modification Supports combined surface treatment and nanoparticle reinforcement Supports optimum filler content and decline at excessive loading

Composite system

Filler/treatment

Key observation

Ref.

NaOH-treated hemp + silane-treated basalt + 1.5 wt.% Si ₃ N ₄ 3–9 wt.% nanosilica Nano-SiO ₂ + silane hybrid interface Silane + SiO ₂ nanoparticle hybrid sizing

FS = 258.91 MPa; FM = 12.48 GPa; optimum S3 Flexural strength improved with nanosilica; optimum loading achieved Improved interfacial, tensile, and flexural properties Improved flexural strength and ILSS through enhanced adhesion and particle dispersion Flexural properties improved up to 2 wt.% but decreased at 3 wt.% because of agglomeration

Hemp/basalt/epoxy

Present study

Sisal/hemp/epoxy

[31]

Basalt/epoxy

[32]

Basalt/epoxy

[33]

Luffa/epoxy

0–3 wt.% nanoclay

[34]

Table 5: Comparison of present flexural results with recent literature. In comparison to previously published nanoparticle-reinforced epoxy systems, the comparison shows that the synergistic combination of alkali-treated hemp fibers, silane-treated basalt fibers, and 1.5 wt. % Si ₃ N ₄ nanoparticles obtained higher flexural strength and modulus. Additionally, the observed decrease in flexural characteristics at greater Si ₃ N ₄ loading (2 wt. %) is in line with previous research, demonstrating that nanoparticle agglomeration restricts the reinforcing efficiency above the optimal filler concentration. Fractographic analysis of flexural fracture surfaces The fracture surfaces of untreated H/B F-Ep (S0ut), which exhibit matrix cracking, fiber pull-out, interfacial gaps, and voids, are depicted in Figs. 5(a) and 5(b). Weak fiber–matrix adhesion and insufficient resin soaking are indicated by the comparatively smooth hemp and separated basalt fiber surfaces with little epoxy residue. The lowest flexural strength (182.35 MPa) and modulus (8.64 GPa) are caused by these flaws, which also encourage early interfacial failure and ineffective stress transfer. Instead of increased energy absorption, the comparatively large deflection (7.1 mm) is linked to early interfacial debonding and decreased structural rigidity. The fracture surfaces exhibit enhanced fiber–matrix adhesion following the alkali treatment of hemp fibers (Fig. 6a) and the silane treatment of basalt fibers (Fig. 6b). The basalt region has less interfacial gaps and debonding, while treated hemp fibers have rougher surfaces, partial fibrillation, improved epoxy coverage, and less fiber pull-out. These characteristics show enhanced interfacial integrity and stress transport, leading to increased modulus (10.12 GPa) and flexural strength (218.44 MPa). The surface treatments improved stiffness without appreciably reducing deformation capability, as seen by the small rise in maximum deflection to 7.4 mm.

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