Re: About the moment calculation in cohesion-friction model

```Hi,

```
What law to choose for your material and what class to use in Yade are different questions I think. CohesiveFrictional law was designed to give the most general cohesive law (even creep is included). The "PM" version as very few differences with the original, and the features it adds could (should) be implemented in CohesiveFrictional as well. Also note that CF law adds torsional stiffness, which (IIRC) is not in Plassiard model (neither is there a plastic limit on this one, but it could be added too).
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Happy to help.

Bruno

On 19/09/10 05:45, 焦利青 wrote:
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```Hello Bruno,

```
Thank you for your so warm help. According to your reply, I think I can understand this law totally. Thank you again. I think you said is reasonable. But, now I am confused at which law is suitable for my model, instead I haven't confused at the law itself. I just want to simulate the almost perfect elastic-plastic material. Compared to CohesiveFrictionalPM, wether this law is better? The different moment threshold criteria should play the varied effect. However, how much effect on the model? Maybe the one law is suitable to the one kind of material, and the other laws are suitable to the others. If you have no idea, I will try. According to the deformed shape and the stress-strain curve, the suitable law will be chosen. If you have any comment, please don't hesitate to let me know. Thank you. if necessary, I will make the change in source, then I will discuss it in here. Thank you. :)
```
Best
Liqing

```
At 2010-09-18 01:29:03，"Bruno Chareyre" <bruno.chareyre@xxxxxxxxxxx> wrote:
```
Hello Liqing,

You are right on the fact that there is no plastic limit for
moment in current law. The calculation of moment itself however
(say, elastic rotation-moment law) should be the same as in
Plassiard et al., only the threshold is missing.
Moment will not exactly act all the time, it will act as long as
shear or tensile strength are not exceeded, then the contact is
broken and there is no moment anymore.
It would be nice to implement the plastic limit on moment. Feel
free to do that (maybe using CohesiveFrictionalPM as an exemple,
or maybe you will use this one straight away?) and ping us for
integrating the change in the sources.
Making the default threshold "infinite" will not change the
default behaviour and cannot hurt anybody.

Cheers.

Bruno

On 16/09/10 12:40, 焦利青 wrote:
```
```    Hello,

I found the moment calculation in cohesion-friction model is
different from the traditional algorithm which is listed in the
paper(Jean-Patrick Plassiard etl, A spherical discrete element
model:calibration procedure and incremental response, 209; N.
Belheine etl, Numerial simulation of drained triaxial test using
3d discrete element modeling; Rolling resistance at contacts in
simulation of shear band development by DEM). In the traditional
algorithms, the slider for rolling starts working if the moment
exceeds a value of "eta* Normal force". However, I cannot find
the related code described it. If no any condition to relax the
moment. then the moment will act all the time.  I think it should
be wrong. Maybe I haven't found the right file. May I have your
help? Thank you.

Best
Liqing

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-- _______________
```    Bruno Chareyre
Associate Professor
ENSE³ - Grenoble INP
Lab. 3SR
BP 53 - 38041, Grenoble cedex 9 - France
Tél : +33 4 56 52 86 21
Fax : +33 4 76 82 70 43
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--
_______________
Bruno Chareyre
Associate Professor
ENSE³ - Grenoble INP
Lab. 3SR
BP 53 - 38041, Grenoble cedex 9 - France
Tél : +33 4 56 52 86 21
Fax : +33 4 76 82 70 43
________________

```