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Failer Criteria

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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.

2 Replies Last Post Oct 23, 2016, 9:44 p.m. EDT
Henrik Sönnerlind COMSOL Employee

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Posted: 8 years ago Oct 12, 2016, 9:57 a.m. EDT
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

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

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Posted: 8 years ago Oct 23, 2016, 9:44 p.m. EDT
Hi Henrik,
thank you for your valued replay.

Hi Henrik, thank you for your valued replay.

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