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A contact model with exceptional force related to the distance

Posted 08.01.2015, 06:54 GMT-5 Modeling Tools & Definitions, Parameters, Variables, & Functions, Structural Mechanics Version 4.4 3 Replies

Zheyu Liu
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Hello, everyone. I'm a new user of COMSOL. I want to bulid a contact model with Structural Mechanics Module that the hemisphere contacts a flat plane. The contact pair is used between the spherical surface and the plane. However, I want to add another exceptional force between two surfaces. This force is a kind of surface force existing on the non-contact area next to the contact area. The interactional surface force is proportional to the distance between the calculated point on the spherical surface and the corresponding point on the plane with same values in X and Y axis. The force exists when the distance is close enough. The value of this force on the spherical surface is different due to the different distance to the plane. On the other hand, the flat plane is going to deform elastically so that the distance is a variation in the calculation. I sincerely want to ask how could I exert this force on my model. This would be great helpful to my work.
Thank you!!
3 Replies Last Post 12.01.2015, 08:52 GMT-5
Nagi Elabbasi Facebook Reality Labs
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Posted: 10 years ago 09.01.2015, 23:18 GMT-5
Hi Zheyu,

Yes you can apply a force proportional to the contact gap in COMSOL. This is one way of modeling electrostatic forces, surface tension forces, and adhesive contact. You can use the contact gap in the load definition. For example pressure = C * gap_p1 * (gap_p1 > 0.0) will apply a normal pressure equal to C times the gap only if the gap is positive. COMSOL will take care of updating the gap calculation with deformation. You may need to increase the “Manual control of search distance” contact pair setting so that the gap is more likely to be defined when the surfaces are not in contact. That is because in “standard” contact you don’t really need the value of a big positive gap.

Nagi Elabbasi
Veryst Engineering
Hi Zheyu, Yes you can apply a force proportional to the contact gap in COMSOL. This is one way of modeling electrostatic forces, surface tension forces, and adhesive contact. You can use the contact gap in the load definition. For example pressure = C * gap_p1 * (gap_p1 > 0.0) will apply a normal pressure equal to C times the gap only if the gap is positive. COMSOL will take care of updating the gap calculation with deformation. You may need to increase the “Manual control of search distance” contact pair setting so that the gap is more likely to be defined when the surfaces are not in contact. That is because in “standard” contact you don’t really need the value of a big positive gap. Nagi Elabbasi Veryst Engineering
Zheyu Liu
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Posted: 10 years ago 10.01.2015, 05:15 GMT-5
Dear Dr. Nagi Elabbasi,

Thank you very much for your detailed reply. The way you posted is exactly the one I wanted to use. However, I don't know how to define the gap_p1 as it varys on the force-applied surface in a cylinder-plane contact model.The model I want to simulate is the JKR model (Johnson, K. L., Kendall, K., & Roberts, A. D. (1971). Surface energy and the contact of elastic solids. Proceedings of the royal society of London. A. mathematical and physical sciences, 324(1558), 301-313.). If I could perfectly define the contact gap, it will be easier to achieve the goal. Besides, I have no idea what the “Manual control of search distance” stands for. Would I ask your further explanation? I really appreciate your great reply.
Best regards.

Zheyu Liu
Dear Dr. Nagi Elabbasi, Thank you very much for your detailed reply. The way you posted is exactly the one I wanted to use. However, I don't know how to define the gap_p1 as it varys on the force-applied surface in a cylinder-plane contact model.The model I want to simulate is the JKR model (Johnson, K. L., Kendall, K., & Roberts, A. D. (1971). Surface energy and the contact of elastic solids. Proceedings of the royal society of London. A. mathematical and physical sciences, 324(1558), 301-313.). If I could perfectly define the contact gap, it will be easier to achieve the goal. Besides, I have no idea what the “Manual control of search distance” stands for. Would I ask your further explanation? I really appreciate your great reply. Best regards. Zheyu Liu
Nagi Elabbasi Facebook Reality Labs
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Posted: 10 years ago 12.01.2015, 08:52 GMT-5
You're welcome Zheyu,

The gap is automatically defined by COMSOL when you define and use a contact pair. The variable name will not be exactly as above but you can find it from the list of post-processing variables. Also the “Manual control of search distance” is in the contact pair definition settings.

Nagi Elabbasi
Veryst Engineering
You're welcome Zheyu, The gap is automatically defined by COMSOL when you define and use a contact pair. The variable name will not be exactly as above but you can find it from the list of post-processing variables. Also the “Manual control of search distance” is in the contact pair definition settings. Nagi Elabbasi Veryst Engineering

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