PSI - Issue 57

213 15

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

As shown in Fig. 16, the maximum contact stresses occur on the pinion flank dedendum between the single contact point B and the pitch point C, when it meshes with the gear wheel addendum. The contact stress results reveal that pitting and macropitting can start in the pinion flank dedendum between point B and point C as this area is subject to a high level of contact pressure stresses.

Area of maximum pressure

Fig. 16. Contact pressures along the path of contact

Fig. 17. 3D Contact pressures on contact zone

Area of minimum λ

Fig. 18. Specific lubricant film thickness ( λ) along the path of contact

The specific thickness of the lubricant film varies along the tooth flank during meshing cycle (see Fig. 18), and the maximum film thickness occurs at the pitch point C due to pure rolling. The area between the start of meshing at point A near pinion root and the single contact point B has the lowest lubricant thickness. As the contact pressure stresses and the specific sliding are high compared to other points along the contact path, the risk of micropitting is the highest in this area. The results obtained in terms of the specific lubricant film thickness show that REF and SP gears operate in a boundary lubrication regime (λ <1), in which the surface roughness peaks are in direct contact, which causes plastic deformations due to the very thin film over the whole contact area, thus micropitting (and wear) is likely to occur on dedendum and also addendum areas of the tooth. T he shot peened gears have a higher λ as they have lower R a values than the REF gears. So, the safety factor (Fig. 19) of the REF gear against the micropitting according to ISO/TS