Inconsistency in Theory manual 6.0 and 6.2 - Multiplicative plasticity

Ratul Das Mechanics of Materials

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Dear Community and Moderators,

I am seeking clarification on the flow rule for finite plastic strain with multiplicative decomposition. In COMSOL 6.0 documentation, the flow rule is:

and in COMSOL 6.2 documentation, the flow rule is:

I am confused about which one COMSOL actually uses. Or are they equivalent? Any help will be useful, thank you. Please see the attached screenshots as well.

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Ratul Das


3 Replies Last Post Dec 2, 2025, 3:22 p.m. EST
Jeff Hiller COMSOL Employee

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Posted: 5 hours ago Dec 2, 2025, 10:57 a.m. EST

Hello Ratul,

There was a typo in the 6.0 documentation, which was corrected by version 6.2.

Best regards,

Jeff

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Jeff Hiller
Hello Ratul, There was a typo in the 6.0 documentation, which was corrected by version 6.2. Best regards, Jeff

Ratul Das Mechanics of Materials

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Posted: 4 hours ago Dec 2, 2025, 11:55 a.m. EST

Dear Jeff,

Thank you for your message. I however did some hand calculations and I think the 6.0 documentation was correct (in multiplicative plasticity, the flow rule is written in terms of Kirchhoff stress). I can derive the equation written in COMSOL's equations page from that, please see the bracketed term in the attached screenshot image(4). If I use the equation from 6.2, I do not obtain the Jacobian J, in the beginning of the equation. Could you please elaborate or point me towards the correct reference it was taken from?

Thank you, Ratul

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Ratul Das
Dear Jeff, Thank you for your message. I however did some hand calculations and I think the 6.0 documentation was correct (in multiplicative plasticity, the flow rule is written in terms of Kirchhoff stress). I can derive the equation written in COMSOL's equations page from that, please see the bracketed term in the attached screenshot image(4). If I use the equation from 6.2, I do not obtain the Jacobian J, in the beginning of the equation. Could you please elaborate or point me towards the correct reference it was taken from? Thank you, Ratul


Jeff Hiller COMSOL Employee

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Posted: 35 minutes ago Dec 2, 2025, 3:22 p.m. EST
Updated: 31 minutes ago Dec 2, 2025, 3:26 p.m. EST

The latest version of the documentation (6.4) includes references, see this link. If this does not answer your question fully, I invite you to contact our tech support team.

Best regards,

Jeff

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Jeff Hiller
The latest version of the documentation (6.4) includes references, see [this link](https://doc.comsol.com/6.4/docserver/#!/com.comsol.help.sme/sme_ug_theory.06.033.html). If this does not answer your question fully, I invite you to contact our tech support team. Best regards, Jeff

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