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a basic question on Drucker-Prager yield function

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(@karn002)
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Joined: 15 years ago

Hi, I have a basic question with regards to the Drucker-Prager yield function, could some one clarify this for me please

The question is, the effective stress for the Drucker-Prager yield criteria is defined to be

Eff_stress = SQRT(3*J2) + SQRT(3)*ALFA*(MEAN_STRESS)

J2 is the second invariant of the deviatoric stress and

MEAN_STRESS = (Sig11 + Sig22 + Sig33)/3

ALFA is some material parameter to be determined

If we consider a case when Sig11 = Sig22 = Sig33 = -SIG, then under such circumstances effective stress would become negative. Which should not happen. Am I missing something, how is this to be understood could someone clarify this for me.

Thanks

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(@jorgen)
Member
Joined: 5 years ago

You are right, the Drucker-Prager model may not yield under hydrostatic compression.

-Jorgen

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