PSI - Issue 57

8

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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The observation of the surfaces in the images above reveals the following points: • On the REF flanks (without shot peening) of the pinion, we can note that: o The micropitting starts on the dedendum flank, at the bottom of the profile.

o Micropitting is present around the pitch line of the pinion, which may have been caused by a stress concentration or more roughness in this area. The occurrence of micropitting is not usual in this area, it is often observed in the tooth dedendum. Similar results have already been obtained in other research from the literature where micropitting is seen in both the addendum and dedendum of the tooth including probably the pitch line (Liu et al. (2019)). o A line of micropitting appears on the addendum flank. o With the test pursuit, the micropitting propagates to occupy a larger area of the pinion tooth flanks as shown in the photos of the Fig. 6 after 0.27*10 6 load cycles. • On the SP flanks (with shot peening) of the pinion, we can note that: o Grinding marks are removed after shot peening. o With shot peening treatment, micropitting appears after the same test time (compared to REF pinion flanks) or earlier. This micropitting also appears below the pitch diameter, this micropitting covers a large part of the tooth dedendum. Qualitatively, we can note that micropitting appears on the shot peened and not shot peened gears flanks. For comparable test durations, the micropitting area on the shot peened flanks (SP) is greater than that on the non shot peened flanks (REF). A difference is observed in the evolution of the micropitting: on REF teeth this evolution is more progressive (micropitting zone extends over the contact zone with the operating time) while on SP teeth it can be seen (visually) that the micropitting zone remains stable for a certain time before the appearance of macropitting (see Fig. 7 and Fig. 8). For all the tests carried out on the shot peened gears and those not shot peened, the micropitting damage on the flanks is initiated at the bottom of the profile in the dedendum zone where the sliding conditions are the most severe. 3.3. Tests until appearance of macropitting/spalling The tests carried out on gears were conducted until the appearance of macropitting/spalling on the teeth flanks. As an example, the images in Fig. 7 show the evolution of the flanks damage of REF and SP pinions after 22 hours of operation (2.97*10 6 ). Micropitting led to widespread spalling on the REF teeth flanks and to macropitting on the shot peened teeth flanks, but after different running times. The appearance of spalling on the REF gears was observed after about 60 hours of operation (on average) whereas on the SP gears, macropitting was observed after about 209 hours (28.2*10 6 cycles), the test was conducted up to 239 hours (32.26 *10 6 cycles) but no widespread spalling on the flanks was observed. Scuffing was also observed on the addendum area of the teeth after 130 hours of running.