Scientific background of YADE, contact law and softening

Asked by ehsan benabbas on 2020-02-06

Hello everyone,

Regarding the scientific background of Yade, I want to find the answer of 2 following questions more than the documentation of YADE:

1- About the theory of plasticity which has been used in "Law2_ScGeom_FrictPhys_CundallStrack()" function.
2- In the stress-strain curve I get from the simulation, I get it as a dense specimen curve with a peak state and steady-state. I am wondering what is the criterion to go for softening after the peak state of the stress-strain curve.

Thank you,
Ehsan

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Last query:
2020-02-06
Last reply:
2020-02-06
Jérôme Duriez (jduriez) said : #1

Hi,

I think we can say that:

1- Plasticity in shear is considered as non-associated (with zero local dilatancy). Looking into the code source may help, as always

2- There is no criterion in itself (from an algorithm point of view, if that was your question). It's the particles themselves, and how they collectively organize in a contact network, which give rise to softening for a dense packing. Scientific literature will be more helpful than our technical forum, here.

[*] https://gitlab.com/yade-dev/trunk/-/blob/master/pkg/dem/ElasticContactLaw.cpp#L78

Chareyre (bruno-chareyre-9) said : #2

Literature will not help in any way I suppose, since the questions are ill
posed.
For the first question i would answer «Coulomb criterion» and that's it.
Associativity and flow rule are not iinvolved since they refer to continua.
Bruno

Le jeu. 6 févr. 2020 08:53, ehsan benabbas <
<email address hidden>> a écrit :

> New question #688544 on Yade:
> https://answers.launchpad.net/yade/+question/688544
>
> Hello everyone,
>
> Regarding the scientific background of Yade, I want to find the answer of
> 2 following questions more than the documentation of YADE:
>
> 1- About the theory of plasticity which has been used in
> "Law2_ScGeom_FrictPhys_CundallStrack()" function.
> 2- In the stress-strain curve I get from the simulation, I get it as a
> dense specimen curve with a peak state and steady-state. I am wondering
> what is the criterion to go for softening after the peak state of the
> stress-strain curve.
>
> Thank you,
> Ehsan
>
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Luc Sibille (luc-sibille) said : #3

Hello,

I think question 2 can be seen as a real scientific question, in the
sense that for a long time it has be assumed by many researchers that
the softening after the peak was the consequence of the strain
localization. That is why many phenomenological constitutive relations
do not describe the softening after the peak.
However, it seems that with DEM softening after the peak may be obtained
without localization (for instance with a low number of discrete
elements limiting the occurrence of strain localization). If the latter
is true it would mean that softening could be seen as a constitutive
response of a granular material.
Nevertheless, I am sure there is a clear study around this question in
the literature and probably it is still an open question... ?

Luc

--
Luc Sibille
Université Grenoble Alpes / IUT1 de Grenoble
Laboratoire 3SR: Sols, Solides, Structures, Risques

Tel lab.: +33 (0)4 76 82 63 48
Tel IUT: +33 (0)4 76 82 53 36

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