Enhancement of mode I/II fracture toughness in basalt/Kevlar hybrid composites via multiwall carbon nanotube integration

Abstract This study investigates the synergistic enhancement of Mode I and Mode II interlaminar fracture toughness (G IC and G IIC ) in basalt/Kevlar hybrid fiber-reinforced epoxy composites through multiwall carbon nanotube (MWCNT) integration. Hybrid laminates with two stacking sequences (B5K10B5 and K5B10K5) were fabricated via vacuum-assisted resin transfer molding (VARTM), incorporating MWCNTs at 0.1, 0.25, and 0.5 wt.% in the epoxy matrix. Fracture behavior was characterized using double cantilever beam (DCB) and end-notched flexure (ENF) tests, complemented by scanning electron microscopy (SEM) to elucidate failure mechanisms. Key results demonstrate that 0.1 wt.% MWCNTs optimally enhanced fracture resistance: K5B10K5 composites achieved 32.9 % G IC improvement (923.42 J m −2 ) and 22.9 % G IIC increase in mode II fracture toughness. B5K10B5 composites exhibited superior baseline G IC (998.61 J m −2 vs. K5B10K5’s 619.47 J m −2 ) but lower G IIC sensitivity to MWCNTs. Performance degradation occurred at 0.5 wt.% MWCNTs due to agglomeration, reducing G IC by 22.5 % in B5K10B5. Conversely, K5B10K5 showed exceptional G IIC (4481.06 J m −2 ) at 0.5 wt.%, attributed to crack bifurcation and shear-induced frictional sliding. SEM analysis confirmed that MWCNTs enhance toughness via crack bridging and fiber-matrix interlocking at optimal dispersion (0.1 wt.%), while agglomerates degraded Mode I performance but partially increased Mode II resistance.