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Failer Criteria
Posted Oct 11, 2016, 2:39 p.m. EDT 2 Replies
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element Hi all,
How to kill element in COMSOL? If the stress of an element exceeds (600 psi as an example), then kill element. I think by reducing the elastic modulus (failure criteria), but I do not know how.
How to kill element in COMSOL? If the stress of an element exceeds (600 psi as an example), then kill element. I think by reducing the elastic modulus (failure criteria), but I do not know how.
2 Replies Last Post Oct 23, 2016, 9:44 p.m. EDT
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Posted:
8 years ago
Hi,
Reducing Young's modulus seems like a good idea.
Note however that
1. If you try to type in an expression in the text field for E of the type
If(solid.mises<600[psi],200[GPa],0.1[GPa])
you will probably run into a 'Circular Dependency' error. This is discussed in many threads in this forum, for example
www.comsol.com/community/forums/general/thread/48995
If you can transform it to a strain criterion, it will be easier.
2. An explicit expression like the one above, has the disadvantage that you may get the stiffness back if the controlling stress or strain decreases. This will for sure happen if you use the stress as criterion.
So you really need to save a state variable so that the expression is of the type
If(failed==0,200[GPa],0.1[GPa])
where the new dependent variable 'failed' switches from its initial value 0 when the limiting stress is exceeded, and never can go back.
3. Loosing stiffness abruptly is not to recommend from a convergence point of view, It is probably better so ramp it down like in a cohesive zone model.
Regards,
Henrik
Reducing Young's modulus seems like a good idea.
Note however that
1. If you try to type in an expression in the text field for E of the type
If(solid.mises<600[psi],200[GPa],0.1[GPa])
you will probably run into a 'Circular Dependency' error. This is discussed in many threads in this forum, for example
www.comsol.com/community/forums/general/thread/48995
If you can transform it to a strain criterion, it will be easier.
2. An explicit expression like the one above, has the disadvantage that you may get the stiffness back if the controlling stress or strain decreases. This will for sure happen if you use the stress as criterion.
So you really need to save a state variable so that the expression is of the type
If(failed==0,200[GPa],0.1[GPa])
where the new dependent variable 'failed' switches from its initial value 0 when the limiting stress is exceeded, and never can go back.
3. Loosing stiffness abruptly is not to recommend from a convergence point of view, It is probably better so ramp it down like in a cohesive zone model.
Regards,
Henrik
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Posted:
8 years ago
Hi Henrik,
thank you for your valued replay.
thank you for your valued replay.