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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Figure 11 compares the tooth bending strength between conditions No. 2 and No. 8. In both cases, 0.2 wt% chopped fibers were added without cloth reinforcement on the gear surface. However, a metallic insert was embedded only in condition No. 8. As shown in the figure, the presence of the metallic insert resulted in an approximately 6.5% increase in tooth bending strength. These findings indicate that embedding metallic insert can slightly enhance gear strength, confirming the importance of increasing the rigidity of the gear rim.

Fig. 11. Tooth bending strength with and without a metallic insert.

3.3. Evaluation of Gear Stiffness Figure 12 shows the stiffness of gears fabricated under each condition listed in Table 2. In this figure, stiffness is defined as the tooth root bending stress (from Figure 6) divided by the rotation angle of the tension arm [rad]. As shown in Figure 12, the gear made of epoxy resin under condition No. 1 exhibited lower stiffness than any of the gears reinforced with carbon fibers. A comparison of conditions No. 2, No. 3, and No. 4 revealed that the number of carbon fiber cloth layers had little effect on the stiffness of the CFRP gears, indicating that the contribution of the cloth to gear stiffness is minimal. Next, comparing conditions No. 3 and No. 5, the gear fabricated using compression molding (No. 3) showed higher stiffness than the one molded without pressure (No. 5). This suggests that proper impregnation of resin into fibers through compression molding is important for improving stiffness. Furthermore, comparisons between conditions No. 2 and No. 6, as well as No. 3 and No. 7, showed that gears containing milled fibers tended to exhibit higher stiffness than those with chopped fibers. This is likely because milled fibers can be more uniformly dispersed in the resin. Finally, a comparison between conditions No. 2 and No. 8 showed that the gear with a metal insert exhibited greater stiffness than the one without. Since the stiffness enhancement due to the metal insert exceeded that from fiber type or compression molding, it can be concluded that reinforcing the rim of the gear with a metal insert is effective for improving gear stiffness.