Yade

Problems with CohFrictMat

Asked by liucheng83

Hi, all
I try to use CohFrictMat to add cohension in my code, but the spheres rotate quckily and cannot go to stable,
how to do with it, thanks before!
-----------------
O.materials.append(CohFrictMat(young=young,poisson=poisson,frictionAngle=radians(compFricDegree),density=density,normalCohesion=1e3,shearCohesion=1e3, isCohesive=1, alphaKr=0.4,alphaKtw=0.4,momentRotationLaw=0,etaRoll=-1,label='spheres_CohFrictMat'))
....
InteractionLoop(
  [Ig2_Sphere_Sphere_ScGeom6D()],
  [Ip2_CohFrictMat_CohFrictMat_CohFrictPhys(setCohesionNow=0,setCohesionOnNewContacts=0)],
  [Law2_ScGeom6D_CohFrictPhys_CohesionMoment()]
 ),
----------------------

If I use the following code, it go to stable,
-----------------
O.materials.append(FrictMat(young=young,poisson=poisson,frictionAngle=radians(compFricDegree),density=density,label='spheres'))
....
InteractionLoop(
  [Ig2_Sphere_Sphere_ScGeom()],
  [Ip2_FrictMat_FrictMat_FrictPhys()],
  [Law2_ScGeom_FrictPhys_CundallStrack()]
 ),
----------------------

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liucheng83 (lcheng83) said : 		#1

The problem is solved when I tried yade-daily. But when I set etaRoll=1.0, warning message is given, how to solve it?
----
WARN /build/buildd/yade-daily-3+3243+42~precise1/pkg/dem/CohesiveFrictionalContactLaw.cpp:156 go: If :yref:`CohesiveFrictionalContactLaw::useIncrementalForm` is false, then plasticity would not be applied correctly (the total formulation would not reproduce irreversibility).
------

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Bruno Chareyre (bruno-chareyre) said : 		#2

" If :yref:`CohesiveFrictionalContactLaw::useIncrementalForm` is false, then... "

Make it true?

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liucheng83 (lcheng83) said : 		#3

Sorry, Bruno, I tried it before with "useIncrementalForm=1", but it seems it has not been solved "https://yade-dem.org/doc/yade.wrapper.html?highlight=law2#yade.wrapper.Law2_ScGeom6D_CohFrictPhys_CohesionMoment" in version 8.0 or before. But it gives new meassage: The maximum value of moments can be defined and takes the form of rolling friction. Cohesive -type moment may also be included in the future. I'm not sure wheter it been solved now.

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Bruno Chareyre (bruno-chareyre) said : 		#4

I'm sorry Liu, I don't understand your problem. Could you maybe explain what contact bahavior you want to simulate?

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liucheng83 (lcheng83) said : 		#5

Hello, Bruno. I just want to test rolling friction with max moment with Law2_ScGeom6D_CohFrictPhys_CohesionMoment. It can be easy seen with the above changes in the yade example "periodic-triax.py". And useIncrementalForm=1 is also tested.

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Bruno Chareyre (bruno-chareyre) said : 		#6

What is the problem with useIncrementalForm=1?
Could you post an example script showing the problem?

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