Two tests were carried out. One with a vegetable oil and the other with mineral oil. The mineral oil viscosity was almost twice than the vegetable oil. It was observed that the Coefficient of friction in case of vegetable oil was lesser than the mineral oil. But the scar formed in case of vegetable oil was larger than that of the mineral oil. The vegetable oils contained some nano particles as additives.
Dear Shubrajit:
This is very interesting but very difficult question to answer in few words. Definitely further analysis should be carried out from your end. First of all, you need to be sure to run the same experiments for at least three times and measure standard deviation and error and be sure that what you are getting is accurate. Hypothetically, you should be sure that you ran the two tests for the vegetable oil and for the mineral oil under same test conditions; include load, speed, environments, etc., then, the difference could be due to failure modes and wear mechanism differences between mineral and vegetable oil. Mineral oil and vegetable oils have totally different chemical formulations. Therefore, you need to start your reasoning from this angle. What you can do, first is to calculate the Elasto-Hydrodynamic Lubrication (EHL) film thickness for both oils, from given viscosity and other parameters included in the EHL equation. Film thickness can give you some insight about scar wear measurements. Another way to back up your conclusions. is to perform Raman analysis in order to find out the chemical components difference between mineral and vegetable oil at the scar locations. Hopefully, you can find chemical residues that might give you a clue of the chemical reaction occurred in the contact area. If all precautions you have taken is sound and correct, it could happen that even though you have low friction, you still have higher wear, but again you can't say this conclusion without doing some EHL calculations and thorough chemical analysis to back up your conclusion. I hope this is will help you somewhat.
All best,
Mohamed F. Alzoubi.
we ran the tests for three readings. the standard deviation for the mineral oil results were found to be 0.006 and that of vegetable oil is 0.00925. the tests conditions were same in all the tests.
Great, then your next step is to calculate EHL for both, then if you have too, you can run Raman chemical analysis to find our residues from the two wear scar. I am pretty sure that EHL will give you an insight of what is going on.
All best,
Mohamed,
It is very hard to tell from just looking at Standard Deviation, therefore, what are friction coefficients for both oils in absolute values?
I have seen quite often reduction of COF accompanied by larger WSD. The simples theoretical explanation is that you are on the right of the Stribeck curve minimum. There, the lower viscosity will decrease both the COF and film thickness, and lower film thickness will lead to higher wear. Unfortunately, your oils differ so much (chemistry, viscosity, nanoparticles) that it is not possible an easy comparison.
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