Issue 78

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

The fracture behavior of the H/B F-Ep hybrid composites was assessed using the SEM fractographs and determined K IC values (Fig. 10). Weak fiber–matrix adhesion and ineffective stress transfer are indicated by the considerable fiber pull-out, interfacial debonding, matrix separation, and pull-out cavities seen in the untreated composite (S0ut; Fig. 10a, b). Higher magnification results in the lowest fracture toughness and limited resistance to crack propagation because cracks preferentially spread along the weak surfaces rather than through the fibers. The primary cause of this behavior is surface contaminants on the untreated hemp fibers, such as waxes, lignin, and hemicellulose, which prevent the fibers from effectively attaching to the epoxy matrix. For untreated natural fiber/epoxy composites, comparable interfacial failure processes have been documented [40].

Figure 10: SEM micrographs of the fractured surfaces of untreated and treated H/B F-Ep after fracture toughness testing: (a, b) S0ut and (c, d) S0t at low and high magnifications.

468