Numerical analysis of hydrogen-assisted rolling-contact fatigue of wind turbine bearings

Abstract

Offshore wind parks at locations further from the shore often involve serious difficulties, e.g. the maintenance. The bearings of offshore wind turbines are prone to suffer hydrogen-assisted rolling-contact fatigue (HA-RCF). Three important aspects linked with bearing failures are being extensively researched: (i) rolling contact fatigue (RCF), (ii) influence of carbide particles on fatigue life, and (iii) local microplastic strain accumulation via ratcheting. However, there is no reference related to bearing failure in harsh environment. This way, this paper helps to gain a better understanding of the influence of hydrogen on the service life of offshore wind turbine bearings through a numerical study. So, the widely used RCF ball-on-rod test was simulated by finite element method in order to obtain the stress-strain state inside the bearings during life in service and, from this, to elucidate the potential places where the hydrogen could be more harmful and, therefore, where the bearing material should be improved.

Role of multiaxial stress state in the hydrogen-assisted rolling-contact fatigue in bearings for wind turbines

“…2b-4b. Within the stress concentration zone, the values of the von Mises stress reach the material yield strength; it implies the appearance of plastic strains near the rod skin, as revealed in previous studies [2,3]. As a consequence of the values of the stress state at the rod surface vicinity, plastic strains are distributed through such a zone.…”

“…The typical profile consist of compressive stresses over 200 μm, tensile stresses for deeper points, and, in the case of radial coordinate lower than 4 mm, a null value for hydrostatic stress is obtained. For completing the analysis of hydrogen diffusion and accumulation on the rod during life in service, the information obtained from the estimation of hydrogen concentration in the radial direction [2,3] can be completed by a discussion of the implications of diffusion in the circumferential direction. To do so, the circumferential distribution of the variables affecting the hydrogen diffusion assisted by stress and strain is plotted in Fig.…”

“…ffshore wind turbines often involve important engineering challenges [1], one of the most important being the improvement of hydrogen embrittlement resistance of the turbine bearings, a key issue in the evaluation of the structural integrity of such components. These elements are prone to suffer the so-called phenomenon of hydrogen-assisted rolling-contact fatigue (HA-RCF) [2,3] as a consequence of the synergic action of the surrounding harsh environment (the lubricant) supplying hydrogen to the material and the cyclic multiaxial stress state caused by inservice mechanical loading [2,3]. Thus the complex phenomenon of progressive damage could be classified as hydrogenassisted rolling-contact multiaxial fatigue (HA-RC-MF).…”

“…To achieve a better assessment of the structural integrity of such components, the analysis of hydrogen accumulation (revealing the prospective damage places) arises as a key issue. In previous studies [2,3], the widely used RC-MF ball-on-rod test [12][13][14][15] was simulated by the finite element method (FEM) in order to obtain the stress-strain state inside the bearings during life in-service. From these states, the hydrogen distribution corresponding to the steady-state in the radial direction of the bearing was obtained.…”

“…From these states, the hydrogen distribution corresponding to the steady-state in the radial direction of the bearing was obtained. This paper goes further in the study developed in previous research [2,3] including the analysis of the hydrogen distributions in hoop and axial directions, in order to obtain the potential fracture places where the hydrogen embrittlement phenomenon initiates.…”