PSI - Issue 57

17

Author name / Structural Integrity Procedia 00 (2019) 000 – 000

Dr.-Ing. D. Jbily et al. / Procedia Structural Integrity 57 (2024) 199–216

215

5. Conclusion The work carried out in this study highlighted the effect of shot peening on the micropitting of gears. The shot peening of the gears resulted in higher residual surface stresses compared with the unpeened gears. Surface roughness parameters also change after shot peening. The experimental results show that micropitting appears on unpeened (REF) and shot peened gears (SP) after approximately the same running time, it initiates in the dedendum flank. The micropitting area on the shot peened flanks is greater than that on the unpeened flanks (REF) for comparable test durations. On REF teeth, micropitting is localized on grinding marks. A difference in the evolution of micropitting between the REF teeth and the SP teeth is also noted. The tooth profile measurements during testing revealed that profile loss is faster on the shot peened gear. The shot peening does not postpone the appearance of micropitting on the gears but rather its evolution towards macropitting/spalling. In comparison to the reference gear (without shot peening), the lifetime of the gear in relation to macropitting/spalling has been increased by more than 60%. This improvement introduced by residual surface stresses is not taken into account in the current standard methods for gear calculation. The experimental results show a good correlation with the analytical study about the appearance of micropitting and macropitting/spalling. The analytical results show that the gears have a specific lubricant film thickness λ less than 1, which is consistent with the fact that all the surface conditions (shot peened and unpenned) led to the appearance of micropitting, but the lowest was observed on the REF gears. The ISO/TS 6336-22 results show good correlation with the occurrence of micropitting on the tooth flanks but high safety factors according ( >2) do not indicate absence of micropitting as demonstrated by the test results. Further studies will be conducted to better understand the results obtained by analysis of the damage mechanisms on the teeth of unpeened (REF) and shot peened gear (SP), tribological tests will be performed to measure the friction coefficient to find correlations with the surface condition after shot peening. Acknowledgements The research project was conducted and funded with the kind support of French Power Transmission committee. References ISO 10825-1:2022, Gears — Wear and damage to gear teeth — Part 1: Nomenclature and characteristics. ISO/TS 6336-22: 2018, Calculation of load capacity of spur and helical gears — Part 22: Calculation of micropitting load capacity. Höhn, B.-R., Oster, P., Emmert, S.,1996. Micropitting in case-carburized gears-FZG micro-pitting test. VDI Berichte, 1230, 331 – 344. Mallipeddi, D., 2018. Surface Integrity of Case-hardened Gears - with Particular Reference to Running-in and Micropitting, Doctoral thesis, CHALMERS UNIVERSITY OF TECHNOLOGY, Gothenburg, Sweden. Winkelmann, L., 2011. Surface Roughness and Micropitting; National Renewable Energy Laboratory, Wind Turbine Tribology Seminar: Golden, CO, USA. Bell, M., Sroka, G., Benson, R., 2013. The Effect of the Surface Roughness Profile on Micropitting. Gear Solutions, 11, 46 – 53. Clarke, A.; Evans, H.P.; Snidle, R., 2016. Understanding micropitting in gears. Proc. Inst. Mech. Eng. C J. Mech ,230, 1276 – 1289. Lambert, R. D., Aylott, C. J. and Shaw, B., A., 2018. Evaluation of bending fatigue strength in automotive gear steel subjected to shot peening techniques. Procedia Structural Integrity 13 1855 – 60 Kobayashi, M. and Hasegawa, K., 1990. Effect of shot peening on the pitting fatigue strength of carburized gears. Proceedings of the IV International Conference on Shot Peening, 465-476. Townsend, D. P., 1992. Improvement in surface fatigue life of hardened gears by high intensity shot peening, NASA Report, Lewis Research Center.