Life Prediction of Large Bearings under Multiaxial Loading Fatigue

• DIRECTORS: Alfonso Fernández-Canteli, Miguel Muñiz-Calvente and Mireia Olave Irizar
• UNIVERSITY: Universidad de Oviedo

Abstract:

The optimum operation of wind turbines is one of the most concerning issues in industry. These structures are subject to the fatigue phenomenon due to loading produced by the wind gusts, reaching the so called failure at the moment the wind turbine’s service stops being the optimum one due to crack initiation. Bearings are one of the most critical components of the wind turbines nowadays. International standards, however, are not suitable for large bearings, and they do not analyse the real loading happening during the estimated life of bearings.

In this thesis a methodology is developed aiming to analyse the loads in realistic terms and reduce the costs produced by the over-design of bearings due to the procedure of the standards. The methodology has alternatives for the calculation of loads on the balls, such as analytic or numeric simulation based ones. The calculation of damage is based on the exhaustive examination of the critical planes following the procedure developed by Papadopoulos, and by the usage of different types of multiaxial fatigue models. Besides, a novel cycle counting method is shown as a derivative model of the rainflow algorithm oriented to an individual cycle analysis.

A number of analyses are made following the procedure of this methodology: the effect on damage of each loading component, the influence on damage of the ball initial position, the effect on damage of rolling contact fatigue and pulsating loads separately, and the beneficial effect on damage of the residual stresses under the bearing raceway. Additionally, some real bearings are analysed using their belonging probabilistic data. This way, a complete calculation of the lifespan of bearings is possible, as well as comparing the proposed models in order to determine which one suits better to the case study and the methodology.