Inquiry for material model ViscoPlastic Drucker–Prager yielding stress

ASPECT
1

Hi everyone!

Recently I am using the Material model ViscoPlastic and implementing yielding stress to it. I seem to find a possible mismatch between the manual and code:

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In the current manual, the yielding stress formula in 3D is (6Ccos(\phi)+2Psin(\phi)) * invpart. But in the code file drucker_prager.cc (my version is v3.1.0) is (6Ccos(\phi)+6Psin(\phi)) * invpart. When I use this part to run a model, I indeed feel that the d\sigma_y/dz is larger than I expect. I am not sure is this function compute_yield_stress no along used or has been fixed in the new version or I just missed something here?
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Thanks for your time!

Best regards,
Xiang He

2

@xiang - Thank you for posting this question to the forum and identifying the discrepancy between the code and documentation.

In short, the code is correct in this case (i.e., see Zienkiewicz and Cormeau, 1974 or Cedric Thieulot’s summary of the topic in his wonderful Fieldstone manual) and the documentation needs to be updated (see this pull request).

Thank you again for identifying this issue and please let us know if you have further questions or concerns you would like to discuss.

John

3

Thank you!