# Frictional Behaviour of the Microstructural Surfaces Created by Cylindrical Grinding Processes
## 5 Conclusions  
Surface microstructural topography is an important factor that directly affects the friction performance of functional surfaces. Due to the different surface creation conditions, the impact of microstructure on friction is different even under a full lubrication. By studying the friction behaviours of ground textural surfaces together with polish-ground surfaces under the different test conditions, some interesting conclusions can be drawn.  
(1) Suitably defined microstructural cylindrical surface created by grinding can possess lower COF than the polish-ground smoother surface does. The best improvement in this study was 20%.  
(2) The investigation shows that the COF decreased with the workload increases but varied insignificantly with the rotational speed changes.  
(3) Textural features of microstructural surfaces have strong effects on the friction behaviour in addition to the normal load or rotational speed applied in the tests. In the range of investigation conditions, it is found that the COF does not vary monotonically with the textural features. Surface with small textural gauge depth of 1-2 micros showed better friction behaviour in the tests.  
(4) Most conventional surface roughness is important to depict the surface geometrical features statistically, but they do not effectively reflect the influence of microstructure on friction behaviour. Most correlation coefficient values between the conventional surface roughness parameters and the COFs are low, only the correlation of the COFs with \(S_{k}\) and \(S_{nk}\) show relative high values. The investigation failed to find suitable functions that can present the COF with conventional surface roughness parameters. This means that conventional surface roughness parameters may not present the COF effectively.  
(5) It is an exciting discovery that the COF could be simply presented by a suitably selected function of dimensionless geometrical feature parameters with very high determination factor. The function with the highest determination factor of 0.97 covers the key microstructure feature parameters in this study. These key parameters are the length, width and depth of the textured gauges together with the dressing lead that determines the gauge structure distribution on the ground surface. This finding provides a good way to identify the best dressing and grinding conditions for creating a textured microstructural surface of  
Figure 9: Surface COF expressed as a function of microstructural geometrical features \((f_{d}\,l_{w})/(b_{w}\,a_{p})\).  
a lower COF. It could bring some significant impacts on energy saving and improvements in bearing energy efficiency.  
Conceptualization, X.C. and H.C.; methodology, X.C.; validation, H.C., X.C., H.L. and C.S.; formal analysis, H.C. and X.C.; investigation, X.C. and H.C.; resources, X.C., H.L. and C.S.; data curation, X.C. and H.C.; writing--original draft preparation, H.C. and X.C.; writing--review and editing, X.C.; visualization, X.C. and H.C.; supervision, X.C. and H.L.; project administration, X.C. and H.L. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Not applicable.  
All relevant data are presented in the paper.  
The authors declare no conflict of interest.