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[Jan Stránský <question694492@xxxxxxxxxxxxxxxxxxxxx>]

Question #694492 on Yade changed:
https://answers.launchpad.net/yade/+question/694492

    Status: Open => Answered

Jan Stránský proposed the following answer:
Hello,

TLTR: the fact that stiffness is same in tension and in compression has
influence on "almost nothing".

> And I posted one similar question

normally we try to force separate question for separate question /
topic, but here maybe it would have been reasonable to continue at the
other thread..

=====
In general:

you have a (let's call it as) micro-mechanical model.
There are several ways how to interpret it (on macro level).
- as particulate material (particles correspond to real grains, interactions correspond to real interactions)
- as continuous material (particles are just artificial discretization, interactions model somehow in discrete manner the continuous stress field)
- as a truss structure (particles has no real interpretation, interactions (network) represent real trusses)
- ...
- ...
- infinitely many other options

Also, there are maaaany options how to model "cement" and consequently how to deal with (not only) this tension/compression stiffness problem.
- grains are modeled by single particle  X  grains are modeled by multiple particles
- cement is modeled as interactions between grain particles  X  cement is modeled by particles
- ... again maaany other options and combination of options

> The normal stiffness of compression and tension is the same in the
definition, does that mean the macro-material is one phase?

No. At least not necessarily.
The fact that stiffness is the same in tension and compression has no implicit influence on phases (however you define it).
>From my point of view, the phases are (should be) more related to stiffness (or other material parameters) VALUES.
See above, you have model, you can interpret it in many ways, including interpretation of phases.

> two particles are connected by cement, if they have the same tension
and compression stiffness, does that mean that the cement has the same
mechanical properties as particles.

No. At least not necessarily.
The fact that stiffness is same in tension and compression has no influence on the relation of "cement" and "particles" mechanical properties..
Note that in yade, interaction and material of particles may be independent (if you change material of particle, it has no effect on existing interactions).

> Assume that cement is very soft and particles are hard, I think the
tensile stiffness would be much smaller than compression.

No. At least not necessarily.
What does "soft" and "hard" exactly mean? Low and high stiffness? Low and high strength?
Anyway, no reasonable "soft" and "hard" definition has influence on different values in tension and compression..

Don't you mix stiffness and strength? Then your concerns would make much
more sense..

> So is this situation could be realized by Yade?

There are several options:
- implement a new material model to fit your needs
- model "cement" differently than just by one interaction. E.g. model the cement phase with small particles, some bonded with both connecting "grains", some not. Then naturally stiffness would be different in tension and compression from the "frict phys" nature of non-cohesive parts of the cement.
- ...

But first you should clarify (to yourself) WHAT you want to model. The question seems to be full of confusion and suggests that this step is not yet solved.
"How" step does not make sense before.

cheers
Jan

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