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[Nima Goudarzi <question668213@xxxxxxxxxxxxxxxxxxxxx>]

New question #668213 on Yade:
https://answers.launchpad.net/yade/+question/668213

Hi,

I’m trying to model a direct shear test using a newly implemented model into YADE. This is a while that I’m trying to obtain reasonable shear stress-shear strain curves with no success. Actually this simulation is a part of my model verification. I have several doubts and questions when simulating: 

1- My contact model has been developed for sand and accounts for rolling and twisting resistances as well  as for  circular contact area and surface crushing parameter. I’ve coded this for sphere to sphere contact only and clearly this is not suitable for sphere-container (facet, box or even wall) interaction  and I am trying two use 2 different materials (both are FrictMat but with different properties for soil and container). Do I need to use two Ip2’s and 2Laws in my simulation[I mean python script] (one for sphere-spher by which I can change my model parameters) and one for sphere-container? Or only one is sufficient?

2- I know that overlap is an essential assumption for YADE dem and we can’t avoid it. I have a weird issue regarding this. As the normal consolidation (before shearing) induces some overlaps, when the shearing phase starts, particles of the bottom box (I move bottom box in shear) tend to fly out when their surface becomes free. This leads to missing some particles in the bottom box which drastically influences the shear stress I measure. Also, even though I consider zero gravity in my engines, particles in the upper box which now don’t have any contacts with the particles in the bottom box, fall down and this also creates shear response issue. 


3- As I essentially need the container to be frictionless in all over the simulation, how I can make sure that my sphere-container interactions is absolutely frictionless. Even by assigning frictAngle=0 for steel (which is the material of my container), I get unreasonable peak values for shear stress which is indication of existing friction between container and spheres.I have defined my model parameters in Ip2. So I need 2 Ip2’s. How I can make all sphere-container interaction, frictionless?

4- Has anyone recently modeled direct shear with YADE (I have an old script written by luc  scholtes which has a servo Controller and a data collector but it seems that the script has some issue with the engine defined for shearing (this has been introduced globally and make some problems with the normal compaction-at least this doesn’t work for me when I change the contact model). Any helps is highly appreciated if there is any successful script which has been verified either by literature or experiments.

5- I can post a part of my script if it helps for your comments and advices.


Thanks so much 

Nima



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