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Simulating rubber piercing in COMSOL

Posted Jul 15, 2020, 7:45 a.m. EDT Structural & Acoustics, Structural Mechanics Version 5.5 4 Replies

Ajay
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Hello,

I am trying to simulate penetration of a rubber membrane by a solid needle. This needs material failure to be simulated. Basically when the stress in a particular element in the rubber domain reaches the yield strength of the material, that element should be effectively deleted. As comsol doesnt have any such feature, I am trying to change the modulus of the element to a very low value. I use state variables feature introduced in COMSOL 5.5 to store the von Mises stress value in an element at the previous time step and use an if condition to set the young's modulus in the current time step. But the model is failing right after the switch happens in any one element.

Also this method is not completely correct as the von Mises stress in the element which has its modulus value reduced will also reduce due to which the modulus value in this element will switch back to its original value in the next time step.

It would really help if someone could help me out as to how I can pose this problem where the modulus in an element once changed to the new lower value stays at that same value.

4 Replies Last Post Jul 16, 2020, 7:08 a.m. EDT
Edgar J. Kaiser Certified Consultant
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Posted: 4 years ago Jul 15, 2020, 8:00 a.m. EDT

I guess that the time dependent solver fails because the procedure generates a very fast derivative. You may need to smooth the transition with respect to time and make sure the solver is appropriately sampling the transition.

Cheers Edgar

-------------------
Edgar J. Kaiser
emPhys Physical Technology
www.emphys.com
I guess that the time dependent solver fails because the procedure generates a very fast derivative. You may need to smooth the transition with respect to time and make sure the solver is appropriately sampling the transition. Cheers Edgar
Ajay
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Posted: 4 years ago Jul 15, 2020, 8:32 a.m. EDT

Hi Edgar,

Thank you for your time. I did think of this but the issue is that I dont know at what time step the mises stress reaches the yield value. I cant use a ramp function as that would need me to have access to the time at which to start the ramp which is an implicit value which I dont have.

Also what is your opinion about the use of if conditional statement? As i stated in my first post, its a double edged sword. Though it switches the modulus to a lower value at the defined condition, on changing the modulus, the mises stress falls below the threshold which would make the if statement to switch the modulus back to the higher value in the next time step.

Any suggestion to overcome this would be really helpful.

Thank you

Ajay

Hi Edgar, Thank you for your time. I did think of this but the issue is that I dont know at what time step the mises stress reaches the yield value. I cant use a ramp function as that would need me to have access to the time at which to start the ramp which is an implicit value which I dont have. Also what is your opinion about the use of if conditional statement? As i stated in my first post, its a double edged sword. Though it switches the modulus to a lower value at the defined condition, on changing the modulus, the mises stress falls below the threshold which would make the if statement to switch the modulus back to the higher value in the next time step. Any suggestion to overcome this would be really helpful. Thank you Ajay
Edgar J. Kaiser Certified Consultant
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Posted: 4 years ago Jul 15, 2020, 8:51 a.m. EDT

Ajay,

check this blog contribution to learn how to track extrema using additional equations: https://www.comsol.com/blogs/using-the-previous-solution-operator-in-transient-modeling/

Hope it helps, Edgar

-------------------
Edgar J. Kaiser
emPhys Physical Technology
www.emphys.com
Ajay, check this blog contribution to learn how to track extrema using additional equations: https://www.comsol.com/blogs/using-the-previous-solution-operator-in-transient-modeling/ Hope it helps, Edgar
Henrik Sönnerlind COMSOL Employee

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Posted: 4 years ago Jul 16, 2020, 7:08 a.m. EDT

Hi Ajay,

As comsol doesnt have any such feature

The Activation node under Linear Elastic Material does exactly what you are trying to achieve.

As the membrane is made out of rubber, maybe an hyperelastic material would be a better choice, depending on the size of the strains. Since you are mentioning Young's modulus, I assume you are currently working with linear elasticity.

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Henrik Sönnerlind
COMSOL
Hi Ajay, > As comsol doesnt have any such feature The **Activation** node under **Linear Elastic Material** does exactly what you are trying to achieve. As the membrane is made out of rubber, maybe an hyperelastic material would be a better choice, depending on the size of the strains. Since you are mentioning Young's modulus, I assume you are currently working with linear elasticity.

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