Discrete acoustic emission waves during stick–slip friction between steel samples

The onset of frictional slip has always been somewhat difficult to study due to the fact that access to the contact area is almost impossible and in most cases only indirect measurements can be carried out. In this report the acoustic emission (AE) technique was used to record and study the elastic waves that appear during the transition from static to kinetic friction in a stick–slip experiment carried out using a sheet of soft steel and a clamp of quenched steel. From the results it has been observed that the onset of the slip event is accompanied by an increase in the continuous AE activity and, immediately afterwards, a long train of AE waves. The main characteristic of these trains are the presence of a first wave with a relatively low amplitude and the very high amplitude of the three or four next ones. After these, the train of waves acquires a decaying-amplitude behaviour. This paper describes the AE activity associated with a slip event and discusses how the aforementioned AE waves could be related with the tribological behaviour of the frictional pair during the slip event.