# Discussion Forum

## Geometric deformation calculation problem

Hello everyone,

I'm a beginner with COMSOL and currently attempting to simulate the compression in asperities contact. Under the 2D assumption, I have two rock blocks pressing against each other, where the upper rock block moves downward with a specific displacement per hour, and the lower rock block is fixed.(Fig.1.)

I have some questions regarding the results:

1. Although the upper rock block moves downward over time, it seems that the original frame lines remain in place.(Fig.2.&Fig.3.) Is this because the mesh hasn't actually displaced? Is there a way to make it move?

2. When the contact points are pressed together, they deform, but not in the way I expected.(Fig.4.) Is it possible to simulate the fracture of the contact points upon compression?

Nick

2 Replies Last Post 2024年7月30日 GMT-4 11:28

Posted: 1 month ago

Where the black edges are drawn is determined by a combination of the settings under Plot dataset edges in the settings for the plot group, and the frame selection in the settings for the dataset.

If you want the compressed material to fail, you must first decide on a failure criterion, and then find appropriate parameters. Is it, for example, plastic deformation, or should the material be considered as brittle?

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Henrik Sönnerlind
COMSOL

Posted: 1 month ago
Updated: 1 month ago

Dear Henrik,

Thank you for your reply! the information is help me a lot! Now I finally solve the problem about how to make the frame line remove. By changing the frame from material to spatial!

In this research, I try to use limestone to be the material and consider it as brittle. My expectation is when I give the upper rock block specific displacement per hour to move downward, the contact area should get high local stress and the contact area will gradully increase because the compression is continued. Finally, the local stress will decrease because of the increase of the contact area until it lower than critical stress and stop to fail.

After I set Rankine's Failure criterion and run,the result seems like a little different (Fig.5.). The two point is contact and the area is increase, but the figure looks like they are not actually break more like it's deformed inward. I'm not sure my setting is right or not, or comsol does'nt allow this simulation way?

Nick