Nondestructive electromagnetic monitoring and diagnosis of damage growth in ball bearings

This study evaluates the size of outer race defects of ball bearings during accelerated life testing by analyzing the signal of an electromagnetic sensor. The electromagnetic sensor consists of a pickup coil wrapped around a permanent magnet. When a conductor passes in the static magnetic field, the generated eddy currents are defected as a change of the magnetic field. The autocorrelation method is applied for sizing defects in the early phase of the damage growth and the RMS method is applied for larger defects. With those methods, the growth of the damage is constantly monitored and is shown to be almost linear. (author)