PSI - Issue 80

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

434

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Table 2. Molding conditions of CFRP gears

Additive rate of short fibers

Number of woven clothes

Press molding

Metal insert

No.

Types of short fibers

1 2 3 4 5 6 7 8

None

0

0 0 1 2 1 0 1 0

Yes Yes Yes Yes Yes Yes Yes No

No No No No No No No

Chopped Chopped Chopped Chopped

0.2, 0.4, 0.6, 0.8, 1.0 0.2, 0.4, 0.6, 0.8, 1.0

0.2 0.2 0.2 0.2 0.2

Milled Milled

Chopped

Yes

2.3. Measurement of tooth bending strength of CFRP gears A static bending test at the tooth root was conducted using a universal testing machine (AG-IS, Shimadzu Corporation, Japan) to evaluate the mechanical strength of the CFRP gears. In this test, a tensile load was applied to each gear specimen, and the root bending strength was calculated based on the measured load and displacement. This enabled an assessment of the effects of fiber length and cloth reinforcement on gear strength. Each test condition was repeated four times, and the mean root bending strength was calculated. The tensile loading speed was set to 1 mm/min, and each test was performed at least three times. Figure 3 shows the test fixture fabricated for the experiment. As illustrated in Figure 3, the base plate of the fixture was bolted to the universal testing machine, and the fixed gear, sample gear, and tension gear were mounted so that the sample gear was positioned at the center. Both the fixed gear and the tension gear were made of general structural steel (SS400). Keys were installed on all gears to prevent slippage between the gears and their shafts. Additionally, a key was inserted between the shaft and the holder to prevent rotation of the fixed gear. Torque was applied to the tension gear via a tension arm, which consisted of one component connected to the shaft of the tension gear and another pulled upward by the universal testing machine. By applying a vertical load to the tension arm, a bending moment was generated at the tooth root of the sample gear. The tooth root bending strength σ [MPa] was calculated using Equation (2): = 2 ∙ ∙ (2) where F is the tangential force [N], 2 is the pressure angle [rad], b is the tooth width [mm], m is the module, and y is the form factor [Bhatia, A., (2012)]. The value of y was determined from the diagram showing the relationship between the form factor and number of teeth [The Society of Materials Science, Japan, (2002)].

Fig. 3. Test fixture designed for measuring tooth bending stress.