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Re: [Question #285260]: contact stiffness change y time

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From: Bruno Chareyre <question285260@xxxxxxxxxxxxxxxxxxxxx>
Date: Thu, 03 Mar 2016 11:32:55 -0000
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Question #285260 on Yade changed:
https://answers.launchpad.net/yade/+question/285260

Bruno Chareyre proposed the following answer:
I just checked the reference in #9. IMHO the approach is flawn and its implementation is a nightmare (section 5 as whole is weird on other points to).
Eq. 1 is a pseudo-stiffness derived in the context of monotonic loading (the force is imposed and kept constant for a duration t). As soon as the loading changes in time it is not possible to define "t" properly, actually it would need a convolution of eq. 1 with the loading history... not something you want to do.

If a viscoelastic relation is implemented based on fig.2 then it will give eq.1 automaticaly, as a particular case.
The CohFrict model is actually fairly close to that, it's just the "C_infinity" dashpot which is not there (it is there in Viscoelastic contact model, OTOH, but then the other dashpot is missing).

Bruno

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