PSI - Issue 12

Francesca Curà et al. / Procedia Structural Integrity 12 (2018) 44–51 Author name / Structural Integrity Procedia 00 (2018) 000 – 000

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Fig. 6. Comparison of CoF values for grease: Pin - on - Disk and Spline Coupling results.

From the analysis of Figure 4 it may be noted that the tribological behaviour of the three lubricants is substantially different, even if some analogy can be found. Oil 1 is very fluid and, if a low percent of GNP is present, the CoF decreases; then, with a higher percent of GNP, the CoF increases up to even exceed the value referred to the case of pure oil. Oil 2, much more viscous, shows a decreasing of CoF value for all percent of GNP. The grease emphasizes a similar trend, showing a CoF value lower than that referred to the pure grease even for 10% of GNP. All lubricants highlight a minimum value of the CoF related to different percents of additive. Similar comments can be drawn by observing Figure 5 that presents for all tests the percent variation of CoF values respect to pure lubricants. Finally, Figure 6 reports the comparison between CoF obtained in both Pin-on-Disk and spline coupling tests, in terms of CoF values. Spline coupling tests have been made by the authors in a previous phase of this research activity, with the aim to relate classical tribological tests for lubricants characterization with tribological test performed on mechanical components. Equal percents of GNP have been used for both compounds and mechanical component characterisation. From the analysis of Figure 6 it is possible to highlight that in the real application the CoF values are slightly bigger respect to the ones obtained by the Pin-on-Disk tests, but similar trends may be appreciated. Furthermore, a CoF values for both cases are lower than that referred to pure grease if GNP additives are present.

4. Conclusions

In this paper, the influence of graphene nano-platelets used as an additive in commercial lubricants has been investigated. The aim of this use is to increase the properties of lubricants in order to reduce the coefficient of friction and therefore to improve efficiency and reliability in machines and mechanical devices.