Which model is used to calculate the cohesive force?

Asked by gaoxuesong on 2019-08-14


    I have looked through the document for Law2_ScGeom6D_CohFrictPhys_CohesionMoment. It gives the formula to calculate the contact force. Fn=min(kn∗(un−upn),an). an is the cohesive force. But is there any material to refer to get the detailed description about cohesive force, an?


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gaoxuesong (260582472-9) said : #1

    I have checked the definition of CohFrictMat. So the normalCohesion and shearCohesion is the an and as appeared in the documentation of Law2_ScGeom6D_CohFrictPhys_CohesionMoment?

Robert Caulk (rcaulk) said : #2

Please reference line numbers like this [1] if you wish to solicit a legitimate discussion. Next, it would be helpful if you tried to use the correct geomechanical jargon. In this case "cohesive force" is ambiguous since we do not know if you are referring to a force or a strength. It seems you are not interested in the force, but instead the strength? Strength in cohFrictPhys is defined by an adhesion [2], which has the same units as the force. It is user defined. It is simply a criteria for bond breakage; if the normal force [1] decreases below the user defined adhesion, the bond breaks.

[1] https://gitlab.com/yade-dev/trunk/blob/master/pkg/dem/CohesiveFrictionalContactLaw.cpp#L116

gaoxuesong (260582472-9) said : #3

Thanks. Now i understand the adhesion attribute in the CohFricPhys material and it is a adhesion strength. Sorry i don't understand the c++ code. Is there any papers to help understand the involved theory about the bond breaking when normal force below the defined adhesion strength.
Thanks again.

Robert Caulk (rcaulk) said : #4

I don't think there are any papers on Yade's cohFrictPhys. The closest is probably JCFpmPhys (theory highlighted in [1]) but there are many variations of the original bonded particle model in literature [2].

[1]Scholtès, L. U. C., and Frédéric-Victor Donzé. "Modelling progressive failure in fractured rock masses using a 3D discrete element method." International Journal of Rock Mechanics and Mining Sciences 52 (2012): 18-30.
[2]Potyondy, David O., and P. A. Cundall. "A bonded-particle model for rock." International journal of rock mechanics and mining sciences 41.8 (2004): 1329-1364.

Jérôme Duriez (jduriez) said : #5


You have details about Law2_ScGeom6D_CohFrictPhys_CohesionMoment e.g. in [1].

With respect to doc syntax:

- an in [2] is CohFrictPhys.normalAdhesion (a force quantity) = F_n^A in Eq. (6) of [1]
- on the other hand, CohFrictMat.normalCohesion is a stress quantity (the doc tells it, here), and corresponds to the \sigma_A parameter in Eq. (6) of [1].

[1] https://link.springer.com/article/10.1007%2Fs10035-016-0687-0
[2] https://yade-dem.org/doc/yade.wrapper.html#yade.wrapper.Law2_ScGeom6D_CohFrictPhys_CohesionMoment

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