PSI - Issue 57

Dr.-Ing. D. Jbily et al. / Procedia Structural Integrity 57 (2024) 199–216 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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1. Introduction The industry is increasingly demanding improved gear performance: higher power, smaller dimensions, lower losses, etc. These requirements have increased the need to find solutions to optimize the strength of gears, and in certain industrial sectors these solutions must be low cost. Gear teeth are subjected simultaneously to bending stresses at the tooth root and to Hertzian contact pressure stresses on the tooth flank. These different stresses can lead to different failure modes such as cracking at the root of the tooth and surface damage due to contact fatigue phenomena linked to contact pressure and tribological behavior. Amongst different modes of surface contact failures, micropitting has been increasingly observed in case hardened gears. It was stated that micropitting had become the most limiting factor of gear behaviors (Höhn et al. (1996)). Progress of micropitting degrades tooth profile and increases noise and vibration levels, and further continuation can eventually lead to catastrophe failure in form of macropitting, spalling and tooth fracture (Mallipeddi (2018)). The literature shows that micropitting is remarkably influenced by the specific thickness of the lubricant film and micropitting damage are closely associated with the effect of surface roughness and surface topography (Winkelmann (2011), Bell et al. (2013), Clarke et al. (2016). As a result, there is an increasing interest in solutions involving the surface engineering of gear flanks. Shot peening is a cold working process done to induce residual compressive stresses which improve the resistance to fatigue. Various investigations were performed about the influence of shot peening on the load carrying capacity of gears. It was found that shot peening increases the bending fatigue strength (Inoue et al. (1989), Lambert at al. (2018)) as well as the pitting load-carrying capacity (Kobayashi and Hasegawa (1990), Townsend (1992), Güntner et al. (2017)). Combination of shot peening and superfinishing increases the load carrying capacity against micropitting and macropitting resistance (Kritzler (2014), Koenig et al. (2015)). Previous study conducted by Peyrac et al. (2017) at CETIM aims to use shot peening (conventional shot peening) as low-cost solution to increase the resistance to micropitting by optimizing the surface topography without operation post shot peening as superfinishing. This study allowed to evaluate different types of shot peening and to identify a particular type of shot peening leading to surface topography and surface roughness optimization resulting in a delay of the micropitting apparition. However, this solution has been validated on rollers and through fatigue tests on a twin disc bench. The current study aims to investigate the effect of this identified type of shot peening on the micropitting resistance of the gear tooth flanks and to compare the experimental results with the calculation results based on standard method ISO/TS 6336-22:2018. 2. Gear Specimens The geometric and loading data are based on the two reference documents which describe tests to be conducted on FZG type test rig; FVA Information Sheet No. 54/I-IV (1993) and No. 371 (2003). The macro-geometric characteristics of the test gear teeth are summarized in Table 1. FZG is the Gear Research Center at the Technical University of Munich and FVA is the Research Association for Drive Technology.