Issue 74

A.Ganji et alii, Fracture and Structural Integrity, 74 (2025) 421-437; DOI: 10.3221/IGF-ESIS.74.26

absorption, consistent with its low tensile strength (18.17 MPa) and fracture toughness (1.75 MPa.m 0.5 ). In contrast, the B4C-loaded composites (EBC1 – EBC4, Fig. 8 b-e) display increasingly complex morphologies due to nanoparticle reinforcement. For EBC1 (Fig. 8(b)), the fracture surface shows slight roughening. This indicates initial crack deflection, contributing to a slight tensile strength increase (19.73 MPa, 8.5 % improvement). EBC exhibits a moderately rougher surface with clearly visible cleavage planes, demonstrating enhanced crack pinning and energy dissipation, correlating with a 25 % increase in tensile strength (22.70 MPa). The EBC3 composite, which exhibited the highest tensile strength (31.2 MPa, 71% improvement), displays the roughest and most torturous fracture surface, dominated by a high density of fine, stepped cleavage planes. This complex topography signifies effective crack pinning and deflection, increasing the fracture area and energy dissipation. Furthermore, the strong interfacial adhesion, inferred from the restricted polymer chain mobility in DSC results, enables effective stress transfer from the softer epoxy to rigid B 4 C particles (472 GPa modulus). Conversely, EBC4 shows a rough but less effective fracture surface, with larger and coarser cleavage planes and evidence of nanoparticle agglomeration. These clusters act as stress concentration sites, initiating microcracks and causing a 17% drop in tensile strength (25.8 MPa) compared to EBC3.

Figure 8: SEM images of (a) PE, (b) EBC1, (c) EBC2, (d) EBC3, and (e) EBC4

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