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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Fig. 14. schematic illustrations of crack propagation for gears reinforced with two cloth layers, one cloth layer, and no cloth.

4. Conclusion In this study, CFRP gears were developed by reinforcing epoxy resin with short carbon fibers and further strengthening the tooth surface with carbon fiber clothes. The bending strength at the tooth root was evaluated, and the main findings are summarized as follows. Firstly, molding the carbon fiber cloth along the tooth surface geometry was found to enhance the bending strength of the CFRP gear. When a single layer of cloth was applied to the tooth surface, the crack initiated at the tooth root and propagated inward through fracture of the cloth. In contrast, when two layers of cloth were used, the crack originated at the interface between the inner cloth and the resin due to interfacial delamination. These results indicate that increasing the number of cloth layers, while simultaneously suppressing delamination at the cloth/resin interface, is essential for further improving the mechanical strength of CFRP gears. Secondly, with regard to the reinforcement of epoxy resin using short fibers, it was found that the use of milled fibers was more effective than chopped fibers in enhancing gear strength. The presence of voids within the gear was identified as a major factor contributing to strength reduction; thus, it is crucial to minimize void formation while ensuring homogeneous dispersion of fibers in the resin. Additionally, pressure molding was shown to be indispensable for achieving sufficient resin impregnation into the fibers and thereby improving strength. For both fiber types, an increase in fiber content resulted in improved gear strength. Finally, to further enhance the strength of CFRP gears, increasing the rigidity of the entire gear structure is important. In this regard, inserting a metallic core at the center of the gear proved to be an effective method.