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[Jan Stránský <question265830@xxxxxxxxxxxxxxxxxxxxx>]

Question #265830 on Yade changed:
https://answers.launchpad.net/yade/+question/265830

    Status: Open => Answered

Jan Stránský proposed the following answer:
Hi Behzad,


> It seems that the contact stiffness calculation in YADE is tricky.
> Because, we cannot assign (AFAIK) a certain value of stiffness to an
> interaction.


you can set the stiffness manually: O.interactions[id1,id2].phys.kn =
whatever
Alternatively to make it done automatially, you can implement new IPhys
functor


> The code gets Kn and Ks from the materials properties (young).
>

it is to make the overall stiffness value size independent. If you have the
same sample scaled and preserve material young value, the resulting overall
material stiffness won't change (but if you set specific stiffness value to
interaction and scale the model, the overall stiffness would change). So
there are good reasons for this approach.


> So, I've got a problem here. Imagine we have the following case:
>
> sphere's radius is 1e-3
> sphere's material young=1e4
>
> a loading plate (a box or facet) with a material of young=1e6
>
> with these values the contact stiffness for sphere-sphere contacts is 10
> and that of sphere-plate contact is 19.8.
>
> Thus, we're kind of limited to the maximum value of 20 for plate-sphere
> contacts. However, I need a higher value for this contact to make sure that
> the deformation comes from the material itself and not from the loading
> plate contacts.
>

I am sorry, I don't understand your point here.. What do you mean by
"deformation", "material itself" etc.? :-)

If you have stiff plate compressing compliant spheres, I would expect the
stiffness (deformation) of plate-sphere to be double (half) than
sphere-sphere contact (at least in simple approximation), exactly what you
observe here.. Could you please explain the problem more in detail?

Thanks
Jan

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