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[Hélvio Peixoto <question654408@xxxxxxxxxxxxxxxxxxxxx>]

New question #654408 on Yade:
https://answers.launchpad.net/yade/+question/654408

Hi,

once again I have a question about the JCFPM physics [1]. This time, it is about the Mohr-Coulomb criterion.

In the file [2], line 144, the maximum force allowed for the shear force is set as the sum of the maximum cohesive shear force (user defined via the particle material), and the friction force proportional to the normal force magnitude "Fn". 

Knowing that Fn  = kn * D [3], and that D may evaluate to negative values, Fn will eventually be negative. So, for the cases where Fn < 0:

1 - is it the expected behaviour that negative (tensile) normal forces decrease the shear resistance of the interaction?
2 - maxFs is compared against the norm of the tangential force. If |Fn*frictionAngle| > |phys->FsMax|, then maxFs < 0, and then the contact fails due to shear. Should this be allowed to occur, I mean, a negative maxFs?

Best regards,

Hélvio Peixoto

[1] - https://answers.launchpad.net/yade/+question/644244
[2] - https://github.com/yade/trunk/blob/master/pkg/dem/JointedCohesiveFrictionalPM.cpp#L144
[3] - https://github.com/yade/trunk/blob/master/pkg/dem/JointedCohesiveFrictionalPM.cpp#L118

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