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Contact problem. Spontaneous rupture via friction. Stick-slip model.
Posted 20.05.2015, 07:21 GMT-4 Structural Mechanics 1 Reply
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Hi,
I'm trying to model a spontaneous rupture at a ground fault via friction. Before to do this, I tried some simple tests.
In particular, I tried to model a block sliding on a flat rigid surface, with contact friction and gravity using a time dependent study. I applied to this block a force, progressively increased in time. The friction follows the classical Coulomb law (only coulomb coefficient miu). I imposed various values of miu. I should observe a stick regime until the friction force is overcome by the applied force and, then, the slip regime should start. Instead, I observe that the block slides always, even when the force is very small and miu is very high. I didn't observe difference using different value of miu. I used also the Comsol test case “sliding wedge” but I was not able to see a stick-slip regime. Could you suggest me a solution? Perhaps, is not possible to model the stick-slip regime? I saw also the Comsol test case "contacting_rings" but I didn't find an error in my simple model.
Moreover, I noticed that Comsol accepts all value of miu, also unrealistic (much more of 1). Why?
Many thanks
I'm trying to model a spontaneous rupture at a ground fault via friction. Before to do this, I tried some simple tests.
In particular, I tried to model a block sliding on a flat rigid surface, with contact friction and gravity using a time dependent study. I applied to this block a force, progressively increased in time. The friction follows the classical Coulomb law (only coulomb coefficient miu). I imposed various values of miu. I should observe a stick regime until the friction force is overcome by the applied force and, then, the slip regime should start. Instead, I observe that the block slides always, even when the force is very small and miu is very high. I didn't observe difference using different value of miu. I used also the Comsol test case “sliding wedge” but I was not able to see a stick-slip regime. Could you suggest me a solution? Perhaps, is not possible to model the stick-slip regime? I saw also the Comsol test case "contacting_rings" but I didn't find an error in my simple model.
Moreover, I noticed that Comsol accepts all value of miu, also unrealistic (much more of 1). Why?
Many thanks
1 Reply Last Post 22.05.2015, 02:17 GMT-4
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Posted:
10 years ago
Hi,
This problem type should be possible to solve, so I suggest that you contact support for advice on your specific modeling.
As for the more general question about the allowed values of the coefficient of friction, it is a very common misconception that the value must be less than 1.
As an example, silver sliding on silver is commonly reported to have mu>1. And I think that drag racing tires can have mu>3. But that raises more conceptual questions about what is friction and what is adhesion.
So there is no fundamental reason to limit the allowable input values.
Regards,
Henrik
This problem type should be possible to solve, so I suggest that you contact support for advice on your specific modeling.
As for the more general question about the allowed values of the coefficient of friction, it is a very common misconception that the value must be less than 1.
As an example, silver sliding on silver is commonly reported to have mu>1. And I think that drag racing tires can have mu>3. But that raises more conceptual questions about what is friction and what is adhesion.
So there is no fundamental reason to limit the allowable input values.
Regards,
Henrik