I tested with two different lubricants.
With first lubricant, the coefficient of friction was 0.042 but wear rate was 7.32
But,
with the second lubricant the coefficient of friction was 0.051 but wear rate was 5.43.
How is it possible that with lower coefficient of friction we are getting higher wear rate?
Since you are getting measurable wear rate, your test is operating in either the mixed or boundary regimes of the Stribeck curve: low speed and high load relative to lubricant viscosity, which means the lubricant film is too thin to separate asperities of the contacting surfaces. Additives in the lubricant can react with the surfaces to form tribofilm under these conditions, particularly if the temperature is high and there is some degree of sliding contact. If the tribofilm grows in rough, as is often the case with zinc diakyldithiophosphate (ZDDP), it can raise the coefficent of friction markedly compared to just running the base oil. These rough films however can be highly protective. On the other hand, other additives can form thin smooth films with low friction, but which are not protective.
It's normal situation since generally speaking there is no direct correlation between friction and wear. For instance, one of the lubricants is stronger oxidizing agent and provides the oxide film on the worn surface which is work away and restored again thusly increasing the wear rate but reducing the friction. Or one of the lubricant may decompose and deposit some antiwear particles that fill the valleys and increase the surface area. Depending on the contact condition it may increase friction but decrease wear.
Hello, I think just as Sergei. Operating surface layer formed under the influence of chemical reactions between the material and lubricant, and it affects on the wear properties. Of course, also depends on the load and roughness. Much depends from the kind of lubricant. There are oils which facilitate deformation of surface roughness instead of shear . In this case, wear resistance increased and friction doesn't need to be reduced.
Andrzej
thank you so much dear Mr.Andrzej and MrSergei.
Sir, can I get some lierature /journal links for the same.
The problem is that not only depends on the friction coefficient, but the viscosity of the lubricant, the temperature, the pressure, and many other factor, the way you asked the question is not possible to give you a good answer. Remember that tribology is the Science and technic of wear, and it is a very complicated aspect. I recommend you to use experimental design to get the equations that fit your experiment, and from there you can get a lot of different result, with just a small amount of experiments.
This situation at wear tests can occure very often when at the low friction coefficient you get the higher wear rate. I'm agree with above mentioned authors about effect of many factors on this aspect, because there is not exist the direct relationship between friction coefficient and wear rate.
friction coefficient is a pr0perty that determine in short time, and wear happens in longer time.
You have not said anything concerning to the surface material and lubricant types. If the lubricant is compatible with a surface it may diffuse in the surface gradually and the friction coefficient and wear will increase then.
We experienced low friction and high wear conditions in laboratory ball-on-flat testing as well. A friction modifier additive is believed to have reduced the tribo-film thickness and caused surface polishing. Interestingly enough, in dynamometer testing measurable wear did not occur although a significant reduction in friction was observed. Creating a realistic surface contact pressure is the key to designing a meaningful wear test.
Article An Investigation of Hydraulic Motor Efficiency and Tribologi...
Agree with above mentioned. You should keep in your mind that there is no direct relationship between friction coefficient and wear rate, you can not use one of them to explain the other. One typical example in polymer tribology (in dry conditions) is that if the polymer melting occurs during testing (this often happens), the melted polymer could serve as lubricating layer to reduce the friction coefficient, while the wear rate increases.
terminology is "thermal control regime", I think you could find some papers talking about it by typing these key words on GOOGLE or GOOGLE SCHLOLAR.
Since you are getting measurable wear rate, your test is operating in either the mixed or boundary regimes of the Stribeck curve: low speed and high load relative to lubricant viscosity, which means the lubricant film is too thin to separate asperities of the contacting surfaces. Additives in the lubricant can react with the surfaces to form tribofilm under these conditions, particularly if the temperature is high and there is some degree of sliding contact. If the tribofilm grows in rough, as is often the case with zinc diakyldithiophosphate (ZDDP), it can raise the coefficent of friction markedly compared to just running the base oil. These rough films however can be highly protective. On the other hand, other additives can form thin smooth films with low friction, but which are not protective.
I agree with Grant W. Pollard's answer, if you want to know how to do a research using experimental design, please I can help you, but you have to take into account different factors, as the pressure, temperature, viscosity, for different types of lubricants, and also physical properties of the test sample you are using. Using regression analysis you can get equations where you can observe the relationship between wear and all the factors that can be present in the experiment.
The lubricant reacts chemically with the surface to form a low shear compond thar wear away
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