PSI - Issue 80

Seiji Mitsubayashi et al. / Procedia Structural Integrity 80 (2026) 423–430 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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3. Results and discussion 3.1. Mode Ⅱ interlaminar fracture toughness of CFRTP

Figure 3 shows the results of Mode II interlaminar fracture toughness for different CNF addition rates. Compared to the unreinforced specimens, the addition of CNF to either the carbon fiber (CF) or the polypropylene (PP) led to an improvement in Mode II interlaminar fracture toughness. When CNF was added to CF, the maximum toughness was observed at an addition rate of 0.025 wt%, which was approximately 1.21 times higher than that of the unreinforced specimen. For CNF added to PP, the maximum value was achi eved at 1.0 wt%, showing an increase of approximately 1.41 times compared to the unreinforced case. In both addition methods, however, the fracture toughness decreased when the CNF content exceeded a certain threshold. This reduction is attributed to the aggregation of CNF, which likely caused delamination of the interfacial adhesion between the fibers and the resin.

Fig. 3. Mode II interlaminar fracture toughness for different CNF addition rates.

Figure 4 shows SEM images of the fracture surfaces for specimens with 0.025 wt% CNF added to carbon fiber (CF) and 1.0 wt% CNF added to polypropylene (PP). In both cases, small voids were observed, as indicated by red circles in the figure. These voids are thought to result from the anchoring effect of CNF at the fiber/resin interface, which enhanced interfacial adhesion and contributed to the improvement in fracture toughness. Furthermore, Figure 5 presents SEM observations of the CF surface with 0.025 wt% and 0.075 wt% CNF additions. As shown by the red circles in Figure 5, CNF agglomerates were observed at the 0.075 wt% additi on level. This aggregation likely weakened the interfacial adhesion and subsequently led to a reduction in fracture toughness.

Fig. 4. SEM images of the fracture surfaces for specimens with (A) 0.025 wt% CNF added to carbon fiber (CF) and (B) 1.0 wt% CNF added to polypropylene (PP).