Wednesday, June 22, 2011

What is wall friction? Part 4

Finally, we have come up to one of the many subjects I am hoping to talk about in this blog: modeling of wall friction based on micromechanical parameters such as wall surface roughness, particle shape, particle size distribution, and microfriction values. Wall friction in fact depends on other parameters such as temperature, humidity, particle roughness, etc., but I want to restrict the study to only a few simple and measurable variables.

I hope this is going to be received well by the particle science community since I will be publishing these results pretty soon. One main concern I found during this process is the fact that I used a different tester to measure wall friction. This tester (I am not sure I should talk about it) has the ability to measure static friction, for dynamic friction the procedure has to be changed a little. In both instances the pattern was the same, the measured data had the same trend in the static case as it did in the dynamic case, that problem was solved.

We selected spherical glassbeads as the sample of bulk material because we have a lot of options in the choice of particle size from vendors. Also, the sphericity of these particles (how round they really are) is above 90%. Their particle size distribution by number of particles per size has a small standard deviation (how wide this curve is, I will talk about particle size distribution in another post). We looked at these particles under the microscope and they indeed showed a large amount of sphericity (although it was not measured), the size distribution was measured using laser scattering methods.

To be continued…

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