Microgeometrical influences on micropitting fatigue damage: multi-scale analysis

Abstract

Effective prediction methods are needed by engineers to design parts used in fatigue conditions. In gears, surface fatigue damage is observed at two scales: pitting and micropitting. These two phenomena occur in response to the variation of the local loading on the contact zone between teeth. The loading is influenced by the shape of the teeth and their surface roughness, which induces stress raisers. The pertinent geometrical parameters that determine fatigue lifetime need to be identified, and in this situation improved knowledge is still required. In the current study, seven parameters are used to define a generic tooth roughness profile. The transient mechanical loading acting on this rough tooth in rolling/sliding contact with a smooth tooth is obtained using elastohydrodynamic code. The stress time history is determined by integration so that pitting and micropitting can be predicted using the Crossland fatigue criterion. The analyses were applied to results obtained for 32CrMoV13 quenched and tempered steel for about 50 variations of the generic roughness profile parameters. It was found that pitting (at the position of the maximum Hertzian shear stress) is influenced by four of the parameters, the extent to which the von Mises equivalent stress exceeds the material yield stress in the zone where micropitting occurs is influenced by two parameters, and the fatigue lifetime is influenced by three parameters.

Prediction of microgeometrical influences on micropitting fatigue damage on 32CrMoV13 steel

“…The first analysis is concerned with the results obtained in the case of a rough pinion tooth meshing with a rough wheel tooth (R/R). In addition to a comparison of the results obtained on this current study of the contact between the rough on rough surfaces (R/R) a comparison with those obtained in a previous study [32] for the contact between a rough and a smooth surface (R/S) completes this analysis. The second analysis deals with the influence of nitriding treatment on the main significant parameters of the profile in the case of rough on rough meshing surfaces without nitriding (R/R) and with nitriding (R/R N).…”

“…In the current study, the EHL calculations have been conducted for contact between two rough surfaces having the same roughness profile. The results are compared with the results obtained in a previous study dealing with smooth on rough surfaces [32].…”

“…In order to reduce the failure risk to 10 À 3 for at N cycles, a shift that reduces the Crossland domain was implemented taking into account the assumption of a normal distribution of the experimental fatigue results and the known value of standard deviation on the fitting process. This method was summarised in [32] and is fully described in [42]. These results take into account all the points regardless of the predicted number N of cycles to rupture, for points with 2 Â 10 4 oNr10 7 cycles.…”

“…This calculates the stress component values for each sub-surface point considered as illustrated in Fig. 3 using the method described in [32,33] assuming elastic plane-strain conditions. For each timestep of the EHL calculation, as shown in Fig.…”

Prediction of micropitting damage in gear teeth contacts considering the concurrent effects of surface fatigue and mild wear

“…Oila and Bull [18] and Febre et al [19] describe the relative influence of a range of factors affecting micropitting. Metalographical and morphological aspects of micropitting are described in [20][21][22].…”