PSI - Issue 31

Sanjin Braut et al. / Procedia Structural Integrity 31 (2021) 45–50 Sanjin Braut et al. / Structural Integrity Procedia 00 (2019) 000–000

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each individual cycle. Total damage was then calculated according to Palmgren-Miner rule. Table 2 shows a comparison of damage and fatigue life estimates for different mean stress correction approaches and for cases without and with modified S–N curve application.

Table 2. Estimated damage and life due to effects thermal and centrifugal forces Modified S–N curve S eq ,max , MPa S a ,max , MPa Mean stress correcion Damage

Life, blocks

NO NO NO NO

133,76 133,76 133,76 133,76 133,76 133,76 133,76 133,76

66,87 66,87 66,87 66,87 66,87 66,87 66,87 66,87

NO

6,44E-11 3,21E-10 1,92E-10 2,42E-09 5,35E-10 2,49E-09 1,73E-09 1,72E-08

1,55E+10 3,12E+09 5,19E+09 4,13E+08 1,87E+09 4,02E+08 5,77E+08 5,80E+07

Goodman Morrow

SWT

YES YES YES YES

NO

Goodman Morrow

SWT

From the results given in Table 2, it can be noticed that use of modified S–N curve gives shorter fatigue life. Also, it can be seen that the shortest life predicts SWT mean stress correction, while every mean stress correction approach gives a shorter life compared to the case without the mean stress correction. 5. Conclusions This paper presents stress-based fatigue life assessment of PMSM rotor with mean stress correction and variable amplitude loading obtained as a result of transient thermo-mechanical 3D FEM analysis. To obtain thermal loads (internal heat generation), i.e., eddy current losses in the permanent magnets and iron losses in the rotor laminations a separated electromagnetic 2D-FEM analysis was performed. Mechanical loads, come from centrifugal forces proportional to the square of the measured rotational speed. Transient FEM analysis of reduced rotor model revealed magnet pocket upper filet as the critical stress region. Maximum equivalent stresses in critical region were calculated for 3 laps of electrical race car drive. Rainflow counting technique identified 159 cycles, which represent one block of cycles. Stress amplitudes were then corrected with three mean stress correction models, namely, modified Goodman, Morrow and SWT and compared to modified S–N curve. Total damage was finally calculated according to Palmgren-Miner rule. Analysis of fatigue life showed that every mean stress correction approach gives shorter life compared with the case without mean stress correction. The shortest life gave the SWT mean stress approach. Acknowledgements This work has been supported by the University of Rijeka under the project number uniri-tehnic-18-225. References Babić, M., Verić, O., Božić, Ž., Sušić, A. 2020. Finite element modelling and fatigue life assessment of a cemented total hip prosthesis based on 3D scanning. Engineering Failure Analysis 113, 104536. Baragetti, S., Borzini, E., Božić, Ž., Arcieri, E.V., 2019. On the fatigue strength of uncoated and DLC coated 7075-T6 aluminum alloy. Engineering Failure Analysis 102, 219-225. Baragetti, S., Božić, Ž., Arcieri, E.V., 2020. Stress and fracture surface analysis of uncoated and coated 7075-T6 specimens under the rotating bending fatigue loading. Engineering Failure Analysis 112, 104512. Božić, Ž. Wolf, H., Semenski, D., 2010. Fatigue Growth of Multiple Cracks in Plates under Cyclic Tension. Transactions of FAMENA 34(1), 1– 12. Božić, Ž., Schmauder, S., Mlikota, M., 2011. Fatigue Growth Models for Multiple Long Cracks in Plates under Cyclic Tension based on ΔKI, ΔJ– Integral and ΔCTOD Parameter. Key Engineering Materials 488–489, 525–528. Božić Ž., Schmauder S., Wolf H. 2018, The effect of residual stresses on fatigue crack propagation in welded stiffened panels. Engineering Failure Analysis 84, 346–357. Bayraktar, S., Turgut, Y., 2016. Effects of different cutting methods for electrical steel sheets on performance of induction motors, Proc IMechE Part B: Journal of Engineering Manufacture, DOI: 10.1177/0954405416666899