WoW: Rolling Contact Fatigue of Oscillating Bearings in Wind Turbines

At a glance

• An investigation of rolling contact fatigue in oscillating large-scale roller bearings for wind turbines is being conducted close to a real scale.
• Fatigue tests are being performed on 10 large-scale roller bearings on a test bench using lubricating greases and operating conditions relevant to real-world operation.
• Modern sensor technology, including a method developed by Fraunhofer based on inductive sensors and a measurement system from project partner MML, is being integrated for the early detection of damage initiation.
• Fraunhofer IWES is responsible for the design and procurement of the large-scale test bearings, test planning, the setup and execution of the large-bearing tests, continuous condition monitoring, the analysis of test results, and participation in the calibration and adaptation of the calculation models.

The challenge

To date, there is only a very limited amount of reliable experimental data available for large roller bearings operating under oscillatory movement. Life calculation models and ISO-based approaches have been derived primarily from tests on small bearings and sometimes exhibit significant variations. As a result, it is unclear how well existing standards and calculation models reflect the actual fatigue life of pitch bearings and other slewing bearings. This complicates the design of new generations of wind turbines and the estimation of their life in the field.

The solution

Fraunhofer IWES is developing application-oriented, large-scale test bearings; working with project partners, it is defining practical fatigue test profiles; and conducting fatigue tests under oscillating operation on a test bench, supported by metrological detection of damage initiation. The large-scale results obtained are systematically analyzed and compared with the small-scale tests conducted by the IMKT (Institute for Machine Design and Tribology at Leibniz University Hannover) as well as with existing life calculation models, and are used to refine the models.

The added value

The WoW research project aims to establish a consistent database on rolling contact fatigue in oscillating bearings and to enable the empirical calibration and simplification of life calculation models. This reduces uncertainties in the design of large roller bearings, test programs, and lubricant selection. This is intended to increase the reliability of rotor blade bearings and, in the long term, reduce the operating and maintenance costs of wind turbines.