The kinetic friction is usually defined as a function of sliding velocity. Lets assume there is an increasing trend for the kinetic friction as a function of velocity. During stick-slip sliding the sliding velocity experiences a very large increase in a short period of time. In this condition, the change in the sliding velocity through time shows a number of velocity spikes with very large peaks and the friction force varies correspondingly from static friction to the kinetic friction. This kinetic friction force corresponds to a very large sliding velocity and the question is whether the kinetic friction of stick-slip still follows the same velocity dependency as in steady sliding.
yes,experimental tests show that the friction coefficient in partial slip condition has lower values compared with sliding condition based on displacement amplitudes
read this one i think it'll help you
Article Friction behavior of quenched and tempered steel in partial ...
Thanks Erfan. But my problem is different. The stick-slip I am talking about is the cycles of sticking and slipping that occur consequently when an object is pushed/pulled in one direction.
Stick-slip is a local phenomena. A real object will have multiple points of stick-slip contact. They are each active at different times during the motion.
Are you talking about a model for just one hypothetical point of stick-slip contact? IOW, just one point that is static (stick) then goes kinetic (slip)? If so, I might suggest that you can assume whatever you want about that one point in either the stick or the slip region.
Dear Weimer,
Thanks for your response. I mean stick-slip during sliding of an objected. For example, the attached plot shows Force-Displacement curve of an object subjected to a pulling force. It experiences cycles of stick-slip during the pulling rather than a smooth and steady sliding. My question is how we can make a connection between the Mu_k in this figure that corresponds to velocity spikes and the Mu-k we obtained from Mu_k-Velocity curves. Mu_k-Velocity curves are obtained through constant velocity tests in steady sliding condition.
Interesting results (if for no other reason than that they are in AE units coming from a Canadian university :-) ).
I suspect the connection will be from a consideration of localized stick-slip to macro-stick slip phenomena. Admittedly, my experience in this is also just beginning to build. I will be curious to see what others respond. In the meantime, perhaps you can consider how these results compare with others at different average velocities and normal stresses.
I have not done the tests myself. It is all the result I have. But I am planning to perform couple of tests. I will definitely examine the effect of velocity and normal pressure to see the connection.
The following reference may be helped you to recognize the physical phenomenon of friction:
computational implementation of LuGre friction law in a revolute joint with clearance, by Muvengei, Kihiu and Ikua
Do you discuss macro or micro scale contact problem? In macro scale, I have not seen such behavior in my studies.
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