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[Robert Caulk <question654408@xxxxxxxxxxxxxxxxxxxxx>]

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

    Status: Open => Answered

Robert Caulk proposed the following answer:
Hello Hélvio,

>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".

FsMax is not explicitly defined by the user. FsMax depends on the
particle size and the user defined cohesion [1].

>1 - is it the expected behaviour that negative (tensile) normal forces
decrease the shear resistance of the interaction?

Yes, a negative Fn should decrease the maximum allowable shear force if
we believe Mohr-Coulomb criterion govern the interaction. See Figure 2
of [2].

>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?

Where are you seeing this? The scalarShearForce is compared to maxFs to
determine if the interaction has failed in shear at line 147  [3].

Cheers,

Robert

[1] https://github.com/yade/trunk/blob/master/pkg/dem/JointedCohesiveFrictionalPM.cpp#L285
[2]Scholtès, L., & Donzé, F.-V. (2012). Modelling progressive failure in fractured rock masses using a 3D discrete element method. International Journal of Rock Mechanics and Mining Sciences, 52, 18–30. http://doi.org/10.1016/j.ijrmms.2012.02.009
[3]https://github.com/yade/trunk/blob/master/pkg/dem/JointedCohesiveFrictionalPM.cpp#L147

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