Define the strain weakening value

ASPECT
1

What 's meaning of plasticity strain weakening intervals, Cohesion strain weakening factors, Friction strain weakening factors, especially the meaning of interval? and are the value dimensionless?

how do I define the value?

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Hi @cgw0814 - I apologize, I missed this and a few other posts the last month or so! The strain weakening intervals or simply the range of 'strain magnitudes" over which the friction and cohesion linearly weaken.

For example, if the type of finite strain tracked is ‘plastic strain’, the friction and cohesion will be reduced the their respective weakening factors as a function of the plastic strain (dimensionless value)…

Here is an example:
The plasticity strain weakening intervals or 0.5-1.5 and the cohesion (initially 20 MPa) and friction (initially 30 degrees) weakening factors are 0.25. If the strain magnitude is 0.5 (or less) at a given point in the model, the cohesion and friction will still have their initial value (20 MPa, 30 degrees). If the strain magnitude is 1.5, the values will be 15 MPa and 22.5 degrees (e.g., linear weakening).

Note that in the visco-plastic model there are different ways to track the finite strain magnitude (total verse plastic verse viscous strain) and you can also apply weakening to the viscous flow law. For all the details, please refer to the visco_plastic.cc or visco_plastic.h documentation. As more questions arise, please post them here as well and apologies again for the delayed reply!

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Thanks for kindly answering. Before I see the reply, I refer to some previous studies to figure out this concept, like Allken et al., 2011 https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2011JB008319.

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@cgw0814 The visco-plastic material model can definitely do the type of strain weakening in Allken et al., 2011. Would it be helpful for me to post an example of how to do this in the parameter file?

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Hi, Dr. @jbnaliboff
Do you mean give you an example by myself?

or

Does that paper can help you to make an example?

or something else?

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@cgw0814 - sorry for the confusion, I did indeed mean for me to post an example of strain weakening in the parameter file.

In fact, the easier thing to do is actually look at the test suite (“tests” folder in main ASPECT directory). Within the test folder, look for .prm files that start with “visco_plastic_yield”. These examples will show how to use plasticity with or without strain softening. After looking through these files, please post any follow-up questions!

Cheers,
John

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