| Resumo : |
The wind energy sector expansion is happening at an extraordinary rate worldwide. With that, the reliability of the wind turbine components becomes a relevant factor. The gear transmission arises as the component causing the most significant number of wind turbine critical failures in the last few years. These critical failures appear as a relevant problem since the higher-than-expected failure rates significantly increase the wind energy cost. So, monitoring the integrity of these components is a crucial demand to ensure a long life of the gearbox and the wind turbine. Fatigue failures are usually accompanied by changes in the surface integrity characteristics of the component, giving signs of damage evolution. The possibility to monitor the temporal evolution of surface degradation can bring the opportunity to avoid corrective maintenance, making it possible to identify failures before they become critical. The hypothesis herein stated is that the early stages of a gear contact fatigue mechanism can be detected by monitoring the temporal evolution of the magnetic Barkhausen noise signal. This study's objective is the correlation of the Barkhausen noise signal evolution with the characteristics of surface integrity along with a gearbox service life. The experimental approach was conducted by performing fatigue tests on a gear test rig. During the tests, regular inspections with a Barkhausen noise sensor were performed in the gear teeth to map the evolution of the signal along with the fatigue life. Destructive analyses were performed after the tests, leading to an understanding of which aspects of surface degradation can be related to the Barkhausen noise signal. Monitoring the evolution of the signal in regular intervals during the tests showed three different levels in which the Barkhausen noise signal presents significant differences. The third level appears to correlate with the imminence of a failure, and damage was observed at the surface a few inspections later than the gear reached that level. Before the fatigue failure, a softened area was observed in the near-surface region, up to approximately 40 microns depth. The gears that presented the Barkhausen signal in the third level were also found evidence of subsurface cracks. These phenomenons were also accompanied by a less compressive residual stress region at 20 microns depth from the surface. The surface degradation evolution and the MBN signal appear to have correlational aspects, allowing the MBN signal temporal evolution to detect the early stages of contact fatigue failure. |