Behavior of acoustic emissions at the onset of sliding friction

Detecting the slip using the acoustic emission (AE) technique is useful for condition-monitoring of machinery and equipment. However, the characteristics of the AE signals at the onset of a slip are insufficiently clarified. We conducted friction tests and simultaneously measured the AE signal, friction, and relative displacement of a brass ball in contact with a flat steel plate. The AE signal clearly increased during the slip, and the effective value of the AE signal well-mimicked the sliding speed. In a frequency analysis of the AE signals, the characteristic frequency components increased significantly during the slip. From the obtained data, we also calculated the AE energy and the friction work during the slip. Both values shared a strong proportional relationship.