PSI - Issue 80

6

Author name / Structural Integrity Procedia 00 (2019) 000 – 000

Seiji Mitsubayashi et al. / Procedia Structural Integrity 80 (2026) 423–430

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Fig. 5. SEM observations of the CF surface with (A) 0.025 wt% and (B) 0.075 wt% CNF additions .

3.2. Mode Ⅲ interlaminar fracture toughness of CFRTP Figure 6 shows a comparison of Mode III interlaminar fracture toughness values at various CNF addition rates. Similar to Mode II fracture toughness, the addition of CNF to either carbon fiber (CF) or polypropylene (PP) resulted in improved Mode III toughness compared to unreinforced specimens. The highest value for CF addition was observed at 0.025 wt%, which was approximately 1.33 times higher than that of the unmodified specimen. For PP with CNF addition, the maximum value occurred at 1.0 wt%, representin g an improvement of approximately 1.53 times. This enhancement is attributed to the well-dispersed and kneaded CNF within the PP matrix, which improved the interfacial adhesion between fiber and resin and helped suppress crack propagation. As with Mode II, fracture toughness decreased when the CNF addition exceeded a certain threshold, likely due to aggregation effects.

Fig. 6. Mode III interlaminar fracture toughness values at various CNF addition rates.

Figure 7 shows SEM images of fracture surfaces for specimens with 1.0 wt% and 1.25 wt% CNF added to PP. In the case of 1.0 wt% addition, small holes presumed to be traces of the anchoring effect of CNF were identified. These holes were similar to those observed in Mode II. In contrast, such holes were not observed in the 1.25 wt% case. This suggests that at 1.25 wt%, CNFs aggregated and failed to produce a sufficient anchoring effect, leading to reduced interfacial adhesion between fiber and resin, and consequently, lower fracture toughness.