multiPlas - Dynardo GmbH

interim values or blending with Mohr-Coulomb failure conditions are possible as well. Necessary material
parameters in the ANSYS multiPlas material model DRUCKER/PRAGER are
~
β and σ y .
Both parameters are connected to cohesion and angle of friction by the following formula:
where:
β =
σ~
y
=
3
6 ⋅ sinϕ
( 3 + sinϕ)
6 ⋅ c ⋅ cosϕ
3
( 3 + sinϕ)
6 ⋅ sinϕ
( 3 − sinϕ)
Fig. 3-8 Drucker-Prager yield criterion as circumlocutory cone (left) or inserted to a cone (right).
3.3.5 Combination of flow condition according to MOHR-COULOMB
and DRUCKER-PRAGER or TRESCA and von MISES
As shown in
Fig. 3-8 the MOHR-COULOMB and the DRUCKER-PRAGER yield criterion differ in the elastic stress
domain. The difference of the surrounded area in the deviator cut plane is 15% at the maximum.
For some problem formulations it can be necessary to limit the elastic stress domain to the area given by
the MOHR-COLOUMB yield criterion. In cases if MOHR-COULOMB or TRESCA alone lead to poor convergence
or even divergence, it can be reasonable to use a combination of the yield criteria to stabilize
the numerical computation.
It has to be kept in mind that this combination is reasonable only for numerical stabilization. It leads inevitably
to differences in the results contratry to the sole usage of the yield criterion by MOHR-COULOMB.
The return-mapping of the stress is not commutaded exactly for both criteria – MOHR-COULOMB and
DRUCKER-PRAGER. Therefore, the permissibility of these result has to be checked individually!
β =
σ~
y
=
3
6 ⋅ c ⋅ cosϕ
3
( 3 − sinϕ)
15
USER’S MANUAL, January, 2013