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How to use the Adhesion "Activation criterion" correctly?

Posted Oct 13, 2021, 3:02 a.m. EDT Structural & Acoustics, Parameters, Variables, & Functions, Structural Mechanics Version 5.6 1 Reply

Sören Mechanical Simulations
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Hello,

I have a plate and on top of the plate is a cube. The gap between both parts is 0 mm. Both parts are connected by a contact feature with Adhesion.

I would want to "switch on" and "switch off" the adhesion by using a parameter called "isSticky". For that I use the "Adhesion" -->"Activation criterion" --> "User defined". My simple formular is "isSticky == 1". However, that formular does not activate the adhesive.

I tried "solid.gap<=0" which works fine. Because of that I tried a combination of both "(isSticky == 1) && (solid.gap<=0)". Unfortunately, it doesn't work too.

I haven't change any other default values. I use Comsol 5.6 on a Windows 10 computer. I simulate a stationary simulation.

How do I use the "Activation criterion" correctly?

Thanks for your help!

Sören

1 Reply Last Post Oct 25, 2021, 6:23 a.m. EDT
Sören Mechanical Simulations
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Posted: 3 years ago Oct 25, 2021, 6:23 a.m. EDT

Hi,

I asked the Comsol support and I am allowed to share there answer on my question with you. However, the support asked me to mension the following statement.

"However, I found it necessary to underline that the file answers the question you have asked but not a general solution for all the related questions of that type."

And thats the solution... " I checked the model that you sent to us. When the slip is computed incrementally and when the adhesion condition is triggered, we consider the adhesive to be enabled; however, there is no relative displacement or slip at that point. Hence we can only compute the adhesive forces in the following increment. But if you would have taken one additional step in the auxiliary sweep, the solid.adhesion would then become 1. * One way to model the on/off switch behaviour that you described is running a pseudo-time continuation and having the isSticky condition set by an interpolation function of pseudo-time. I have modified the model that you sent to us to demonstrate such a model.

In the modified model, I have defined a pseudo time parameter para in the Parameters 1 node. Then I have defined an interpolation function, Defintions>Interpolation 1 node, that is zero in the beginning and stays as 1 in the following increments. Next, I set isSticky parameter using that interpolation function in the Variables 1 node .

When you check the Results>Is Adhesive Active node, you will see that the adhesion condition is zero for 0 and 1, and for the rest of the values, it is 1 therefore active. I hope this helps. Please let me know if you have further questions. "

Thanks again to the Comsol support and I hope this answer will help also other people with similar problems.

Greetings S

Hi, I asked the Comsol support and I am allowed to share there answer on my question with you. However, the support asked me to mension the following statement. "*However, I found it necessary to underline that the file answers the question you have asked but not a general solution for all the related questions of that type.*" And thats the solution... " *I checked the model that you sent to us. When the slip is computed incrementally and when the adhesion condition is triggered, we consider the adhesive to be enabled; however, there is no relative displacement or slip at that point. Hence we can only compute the adhesive forces in the following increment. But if you would have taken one additional step in the auxiliary sweep, the solid.adhesion would then become 1. * One way to model the on/off switch behaviour that you described is running a pseudo-time continuation and having the isSticky condition set by an interpolation function of pseudo-time. I have modified the model that you sent to us to demonstrate such a model.* *In the modified model, I have defined a pseudo time parameter para in the Parameters 1 node. Then I have defined an interpolation function, Defintions>Interpolation 1 node, that is zero in the beginning and stays as 1 in the following increments. Next, I set isSticky parameter using that interpolation function in the Variables 1 node .* *When you check the Results>Is Adhesive Active node, you will see that the adhesion condition is zero for 0 and 1, and for the rest of the values, it is 1 therefore active. I hope this helps. Please let me know if you have further questions.* " Thanks again to the Comsol support and I hope this answer will help also other people with similar problems. Greetings S

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