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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:
> normal stiffness ... and has to be related to E of particles
> is there any ways ... the stiffness is independent to E of particles

The interaction stiffness **IS** independent of E of particles.
The interaction stiffness **does not need to be** related to E of particles.
If you do nothing about it, the (very reasonable) default behavior is that the interaction stiffness is harmonic mean of particle stiffnesses.
But you have several ways how to make it less or more independent:
- using MatchMaker (if Ip2 supports it) and its "algo" or even "val" to break the dependency
- modifying interaction properties directly, for i in O.interactions: i.phys.kn = whateverDependentOrIndependentValue
- set some particle material, create "default" interactions based on current material, assign different material to the particles (has no effect on existing interactions)
- ... ?

> I am still wondering that is there any ways to define the stiffness of
a pair of compression and tension differently

I am afraid a new contact law is necessary..

As you mentioned FrictPhys, it already has different stiffness for tension and compression.
The disadvantage is that the tension stiffness is 0 and cannot be adjusted.. :-)

> If I would like to model the cement as the interaction between
particles.

I see two easy approaches. Assuming you have the desired packing, you
can

1)
- set real material to particles (particles have "good" properties)
- crate initial cohesive interactions (interactions have "wrong" properties)
- modify interactions to match concrete properties (interactions now have "good" properties)

2)
- set auxiliary "concrete" material to particles (particles have "wrong" properties)
- crate initial cohesive interactions (interactions have "good" properties)
- set real material to particles (particles now have "good" properties)
(recall that changing particles' material has no effect on existing interactions)


cheers
Jan

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