Experimental investigation on acoustic emission in fretting friction and wear of bolted joints

Fretting between bolted interfaces may change the dynamic characteristics of structures under vibration loading. The acoustic emission (AE) technique has been successfully used to investigate friction and wear mechanisms between different kinds of contact pairs. This paper experimentally investigates the AE signals of a bolted joint structure during friction and long-time fretting wear to explore the relationship between AE characteristics and interface fretting behaviors. A test apparatus dedicated to the study of fretting behaviors of bolted joints together with an AE acquisition system is used to carry out the experimental tests. Relative displacement, tangential friction force and the related AE waveform features are obtained simultaneously to better relate acoustic emission signals with hysteresis loops. The effects of external excitation amplitude and fretting wear cycles are investigated. The frequency signatures of the individual burst acoustic emission event under different excitation amplitudes and wear stages are analyzed. Results show that AE events mainly occur in the micro-slip and the gross-slip regime, and AE technique is more sensitive to the transition point from micro-slip to gross-slip regime. As the external excitation amplitude increases, the value of most AE parameters is gradually increased. As the fretting wear cycles increase, evolutions of bolt preload, frictional coefficients, and AE parameters first show a significant change and then become asymptotically stable. Furthermore, the frequency intensity and range will increase with the increase of excitation amplitude and decrease with the wear cycles.