The influence of contact time and event frequency on acoustic emission signals

Abstract

Studies of acoustic emissions (AE) of rotating machine elements is often performed under a constant speed. There are few investigations on speed and contact time dependency of acoustic emission signals, even though some investigations have reported difficulties at elevated rotational speeds. Simplified experiments are, therefore, presented in this article to increase the understanding of the time dependency of acoustic emission signals. Hertzian impacts and tensile tests are used to study contact time, the time duration of an event and offset time, the time between events and accordingly the event frequency. The results of these model experiments indicate an indirect quadratic proportionality of acoustic emission amplitudes and contact time ( $u_{max}\propto 1/(t_c^2)$ ), as well as a proportional relationship between the root mean square and event frequency ( $\mathrm{RMS}\propto f_{\text{event}}\propto 1/t_{\text{offset}}$ ). The relationship between contact time and the root mean square of acoustic emission signals is strongly dependent on the damping of the system.