# Stick-Slip Phenomena and Acoustic Emission in the Hertzian Linear Contact
## 5 Conclusions  
The acoustic emission signals generated during the relative motion between the cylinder-plane specimens were captured by a multipurpose acquisition system and processed using basic parameters based on the RMS signal in order to determine if the stick-slip appearance and their sensitivity to the onset of movement can be detected and predicted by the acquisition and analysis of the AE using hardware and software with low demand. The tests were conducted under various situations involving normal loads, driving, and sliding velocities. Although the tests were not exhaustive, they verified the feasibility of using non-complex AE parameters as a non-destructive method of detecting the stick-slip phenomenon.  
In all tests performed, the presence of the stick-slip phenomenon was confirmed by the COF variation and the coincidence with the bursts of AE for all contact pressures and driving and sliding speeds. The variables that significantly affected the changes in friction coefficients were the driving speed, sliding speed, and normal load. Higher normal loads and slower displacement speeds increased the slip velocity because of the low-frequency, high-amplitude stick-slip phenomena that occurred mostly at the start of the slide movement.  
AE is related to this type of motion. In terms of acoustic emission, the stick phase had low AE activity, while the sliding phase exhibited bursts of high amplitude activity that were reliant on the normal load. Jumps from static to kinetic friction (COF) were followed at short time intervals (milliseconds) by acoustic emission (AE) jumps.  
The presence of the stick-slip phenomenon can be detected by measuring the amplitude and energies of the acoustic emission revealed by a high positive Pearson correlation between them. The energy consumed by friction (\(W_{\text{COF}}\)) increased with the amplitude of the stick-slip motion, and the energy generated by AE increased also.  
The amplitude and energies generated by the acoustic emission are relevant and confirm the direct dependence on the stick-slip phenomena for the non-lubricated Hertzian linear contact, while the count of AE bursts is not applicable to identifying the magnitude of the stick-slip movement, probably due to the same amount of real bursts missing caused by the relatively low sampling frequency used in this work.  
Hence, the acoustic emission detected by analysing the parameters that can be used from a signal captured from a multifunctional platform becomes an essential indicator for detecting and monitoring the stick-slip phenomenon.  
Conceptualisation, L.M.B., A.T. and J.R.; methodology, L.M.B., A.T. and J.R.; software, L.M.B.; validation, L.M.B.; formal analysis, L.M.B., A.T. and J.R.; investigation, L.M.B., A.T. and J.R.; resources, L.M.B., A.T. and J.R.; data curation, L.M.B., A.T. and J.R.; writing--original draft preparation, L.M.B.; writing--review and editing, A.T. and J.R.; visualisation, L.M.B.; supervision, A.T. and J.R. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Not applicable.  
The authors declare no conflict of interest.