PSI - Issue 80

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

440 10

Fig. 12. stiffness of CFRP gears fabricated under each condition listed in Table 2.

3.4. Observation of Cracks in CFRP Gears Figure 13 shows the cross-sectional observations of gears after fracture. Figures 13(a), (b), and (c) show the fractured surfaces of a gear without surface reinforcement using cloth and containing 1.0 wt% chopped fiber, a gear reinforced with one layer of cloth and containing 1.0 wt% chopped fiber, and a gear reinforced with two layers of cloth and containing 0.2 wt% chopped fiber. Based on the fracture patterns observed in these gears, schematic illustrations of crack propagation for gears reinforced with two cloth layers, one cloth layer, and no cloth were created and are shown in Figure 14. From the comparison, it was found that the gear without cloth reinforcement fractured from the tooth root. The gear reinforced with one layer of cloth showed a failure sequence in which a crack initiated at the tooth root, the cloth layer subsequently ruptured, and finally the crack propagated further inside the gear body. Additionally, the gear reinforced with two cloth layers exhibited two types of failure behavior: one similar to that of the single-layer case, and another in which delamination occurred at the interface between the inner cloth and the resin, followed by crack propagation into the interior of the gear root. These findings suggest that, to further improve the strength of CFRP gears, it is necessary not only to increase the number of cloth layers but also to suppress delamination at the cloth-resin interface.

Fig. 13. Cross-sectional observations of gears after fracture.