Rolling contact fatigue tests on pre-damaged slewing bearings

Blade bearings of wind turbines are grease-lubricated rolling bearings which are operated in an oscillating manner. They can be subjected to both rolling contact fatigue and wear, in particular standstill marks and false brinelling. Rolling contact fatigue arises from alternating stresses due to the passage of rolling elements under high loads, standstill marks and false brinelling occur during cyclic motion and are often exacerbated by inadequate lubrication. In this paper, we want to understand fatigue and the influence of false brinelling on fatigue better and to investigate whether it is advantageous to avoid false brinelling. We performed fatigue tests with four blade bearings. Three of them had existing false brinelling damage. In addition, we repeated tests on much smaller angular contact ball bearings. To contextualize the results, we calculated the fatigue life of a pitch bearing from a reference turbine matching our test bearing design and compared the calculation to the test results. Although the stochastic fatigue behavior in combination with the low number of tests makes it difficult to draw general conclusions, the results indicate that false brinelling shortens fatigue life, even if the blade bearings pass the fatigue test.