Issue 78

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

dispersion, crack initiation and propagation, fiber pull-out, matrix cracking, interfacial debonding, and other failure mechanisms controlling the mechanical behavior of the hybrid composites, were then assessed by analyzing the FESEM micrographs.

R ESULTS AND DISCUSSION Effect Si 3 N ₄ content on Interlaminar Shear Strength of H/B F-Ep hybrid composites he peak load and interlaminar shear strength (ILSS) of H/B F-Ep hybrid composites with various Si ₃ N ₄ contents are shown in Tab. 3. The composite with no treatment (S0ut) had the lowest peak load (1192.2 N) and ILSS (16.25 MPa). The ILSS of the surface treated hemp and basalt fibers increased by 15.51 % to 18.77 MPa for S0t from 18.31 MPa for S0ut. The ILSS was further enhanced with Si ₃ N ₄ incorporation to 24.16, 26.45 and 27.77 MPa for S1, S2 and S3, respectively. Therefore, the ILSS of S3 (1.5 wt. % Si ₃ N ₄ ) was the highest, and this is 70.89 % higher than the ILSS of S0ut. This was also the case for the peak load, which rose from 1192.2 N for S0UT to 1990.8 N for S3. However, excessive loading of Si ₃ N ₄ nanoparticles (S4 = 2 wt. %) was not as effective, with the ILSS decreasing to 26.25 MPa and peak load to 1826.2 N. Composites Peak Load (N) ILSS (MPa) % Increase in ILSS S0 UT 1192.2 16.25 — S0 T 1377.6 18.77 15.51% S1 1595.5 24.16 48.68% S2 1798.9 26.45 62.77% S3 1990.8 27.77 70.89% S4 1826.2 26.25 61.54% Table 3: Peak load and ILSS of Hybrid nanocomposites. After surface treatment, improved fiber–matrix adhesion is responsible for the ILSS improvement from S0ut to S0t. While silane treatment of basalt fibers enhances their compatibility with the epoxy matrix, alkali treatment of hemp fibers eliminates hemicellulose, lignin, waxes, and other contaminants, enhancing surface roughness and encouraging mechanical interlocking. Since well-dispersed nanoparticles can occupy microvoids and interfacial gaps and enable stress transfer, the further rise in ILSS with Si ₃ N ₄ addition suggests improved interfacial integrity. An ideal equilibrium between nanoparticle dispersion and interfacial reinforcement is suggested by the greatest ILSS found at 1.5 wt. % Si ₃ N ₄ (S3). Nanoparticle agglomeration, which can produce localized stress concentrations and favorable crack-initiation sites, is probably responsible for the modest decrease in ILSS at 2 wt. % (S4), which lowers reinforcing efficiency [25]. It is important to mention that the conditions of ultrasonication also affect the beginning of Si ₃ N ₄ agglomeration. The duration of ultrasonication can have a substantial impact on the dispersion of nanoparticles and, in turn, the concentration of Si 3 N ₄ at which particle agglomeration may take place. Therefore, the optimal content found in this study is only relevant to the processing conditions under consideration. Comparing current literature The results of this study are comparable to earlier studies that found that modification of the fiber surface and controlled incorporation of nanoparticles benefited fibers. Kiran et al. [26] reported that, the compatibility and debonding resistance of fiber–matrix were enhanced by silane treatment of basalt fibers. Praveena et al. [27] also attributed the improvements in mechanical properties to better interfacial adhesion, efficient stress transfer, and crack bridging mechanisms. Khan et al. [28] also reported that the addition of eggshell particles in bamboo/epoxy composites showed a maximum flexural performance at optimum amount of eggshell. Somsole and Gopalan [29] also showed that the interlaminar shear performance is also enhanced using ceramic particle reinforcement, with improved fiber–matrix bonding and crack arresting mechanisms. On the other hand, the small decrease seen at the highest Si ₃ N ₄ loading is consistent with Dejene [30] who found that excessive loading of nanoparticles can lead to possible agglomerations, stress concentration at certain locations and premature fracture. Overall, it is believed that the superior ILSS of S3 can be attributed to the combined effect of the effective dispersion of Si ₃ N ₄ and effective surface modification of the fibers, which will improve the bonding at the interface, the stress transfer between the fiber and matrix and resistance to delamination. T

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