PSI - Issue 80

Seiji Mitsubayashi et al. / Procedia Structural Integrity 80 (2026) 431–442 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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chopped carbon fibers without cloth reinforcement on the tooth surface. Figures 6(c) and 6(d) depict the results for CFRP gears reinforced with both chopped carbon fibers and one or two layers of carbon fiber cloth, respectively. In the region where the tooth bending stress is zero, backlash occurs due to insufficient engagement between the gears, resulting in variability in the onset of measured stress. The lowest tooth bending strength was observed for condition No.1 in Table 2, in which the gear was made from neat epoxy resin. In contrast, the highest strength was achieved under condition No.4, where 0.2 wt% carbon chopped fibers were compounded and two layers of cloth were aligned on the tooth surface. Additionally, the epoxy-resin gears exhibited brittle fracture without stepwise stress reduction. In contrast, the gears containing chopped fibers fractured with a gradual decrease in stress regardless of the presence of cloth reinforcement, suggesting the occurrence of interfacial debonding between the short fibers and resin during crack propagation.

Fig. 6. Relationship between the tension arm rotation angle and tooth bending stress for (a) epoxy resin gear, (b) epoxy resin gear with 0.2wt% chopped carbon fibers, (c) epoxy resin gear with 0.2wt% chopped carbon fibers and one layer of carbon fiber cloth, and (d) epoxy resin gear with 0.2wt% chopped carbon fibers and two layers of carbon fiber cloth. Figure 7 shows the relationship between tooth bending strength and the chopped carbon fiber content. The highest tooth bending strength was observed in the gear reinforced with 1.0 wt% chopped carbon fibers and one layer of carbon fiber cloth, which exhibited approximately 2.4 times the strength of the neat epoxy resin gear. Even without cloth reinforcement, the gear with 1.0 wt% chopped fibers demonstrated a strength about 2.1 times greater than the unreinforced epoxy gear, highlighting the strengthening effect of chopped fibers.