PSI - Issue 42

Omar D. Mohammed et al. / Procedia Structural Integrity 42 (2022) 1607–1618 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

1616 10

should be calculated. A safety factor can be obtained for a certain gear load case by dividing the number of cycles till failure Nf by the number of cycles the gear experiences at that load, Eq.3. The SF should at least equal 1.0 for safe operation. In the same way, the safety factor can be represented in stress direction, Eq.4. = ≥ 1.0 (3) = 1 ≥ 1.0 (4) Thus, to assess the designs studied in this research the safety factors in ‘cycles’ and ‘stress’ can be obtained as shown in Table 5. It is worth mentioning that the ‘cycles’ value and the corresponding ‘stress’ value are both representing the same damage status of a certain designed gear which is subjected to a certain load spectrum. To consider the effect of stiffness variation, the results shown in Table 5 consider the average of the stress values obtained from the positions of 0 o and 90 o . Design B shows better SF’s for all studied cases except the case of contact of Gear1 -Ring engagement. However, Design B might be selected for Gear 1 if it is required to reduce the PPTE at the high torque levels.

Fig.10 The obtained cumulative damage of Gear1, Gear2 and Ring Gear using design B for bending and contact

Fig.9 Cumulative damage calculation method

Table 5: Safety factors obtained in ‘cycles’ and ‘stress’ for the studied design cases. Design A SF (cycles) SF (stress) Design B SF (cycles) SF (stress)

SF (cycles)

SF (stress)

Design 0

G1-D Contact G1-C Contact G1-D Bending G1-C Bending G2-D Contact G2-D Bending RG-D Contact RG-C Contact RG-D Bending RG-C Bending

2.12 1.09

1.06 0.93 1.31 1.17 1.27 1.47 1.14 0.93 1.32 1.18

G1-D Contact G1-C Contact G1-D Bending G1-C Bending G2-D Contact G2-D Bending RG-D Contact RG-C Contact RG-D Bending RG-C Bending

1.49

1.03 1.26 1.31 2.10 1.44 1.73 1.11 1.26 1.34 2.17

G1-D Contact G1-C Contact G1-D Bending G1-C Bending G2-D Contact G2-D Bending RG-D Contact RG-C Contact RG-D Bending RG-C Bending

0.01 0.44

0.68 0.69 1.35 1.19 1.13 1.52 0.76 0.69 1.11 0.95

187.35

10.71

10.24

13.69

3.94

1732.02 119.93 4807.98

4.53 4.90

24.50

120.72

262.87

8.82 5.08

6.81

0.05 2.02 2.53 0.64

870.61

11.50

12.48

4.22

858.73

5. Discussion Gear failure is an undesired event that entails costly and serious consequences, as it involves termination of the ability to perform the required function. The selected design has to fulfil the durability requirement, and also has to be compromised in order to fulfil the other requirements. To cover the studied design considerations a certain compromised microgeometry design set that fulfils the different design requirements should be selected. From Figs.3 6, it is clear that using Design 0 (no microgeometry) will produce the worst results, and by adding appropriate