yade-users team mailing list archive

[chiara modenese <c.modenese@xxxxxxxxx>]

On 21 April 2010 16:40, Bruno Chareyre <bruno.chareyre@xxxxxxxxxxx> wrote:

>
>  2. current "trial" shear strain εT is computed*, with corresponding
>> trial stress σT(εT); for admissible state f(σN,|σT(εT)|)<=0, there is no
>> dissipation and the contact is done for this timestep. In case of
>> non-admissible f(σN,|σT|)>0, shear strain is modified** to have new
>> value εT2 so that f(σN,|σT(εT2)|=0; dissipated energy increment is |
>> εT-εT2|*σT(εT2), which is added to cummulative dissipated energy. In the
>> Cpm model, plastic flow rule is non-associated and σN doesn't have to be
>> recomputed again, after changing σT.***
>>
>>
>>> Worth than that : unload the normal component with null shear velocity.
>>> It will meet the plasticity criterion at some point (assuming purely
>>> frictional law). Some elastic energy will be transfered to plasticity with
>>> total dUs=0. I see this special case only now... I'll have to tackle this
>>> even for FrictPhys_basic.
>>>
>>>
>>
>> That works just fine in the scenario described above, as far as I see.
>>
>>
>>
> Interesting. For forces, I used exactly the same formulae that you write
> for strain/stress, and indeed it should work just fine in the special case
> described.
>
> if( shearForce.SquaredLength() > maxFs ){
>       Real ratio = Mathr::Sqrt(maxFs) / shearForce.Length();
>       if (traceEnergy) {//define the plastic work input and increment the
> total plastic energy dissipated
>           plasticDissipation +=
>
> (shearDisp+(1/currentContactPhysics->ks)*(shearForce-prevForce))//plastic
> disp.
>               .Dot(shearForce);//active force
>       }
>
>
> For elastic energy, I don't see any problem(*) in my case :
>
> Real Law2_ScGeom_FrictPhys_Basic::elasticEnergy()
> {
>   Real energy=0;
>   FOREACH(const shared_ptr<Interaction>& I, *scene->interactions){
>       if(!I->isReal()) continue;
>       FrictPhys* phys =
> dynamic_cast<FrictPhys*>(I->interactionPhysics.get());<----------------------------------
> see (*)
>       if(phys) {
>           energy += 0.5*(phys->normalForce.SquaredLength()/phys->kn +
> phys->shearForce.SquaredLength()/phys->ks);}
>   }
>   return energy;
> }
>
> I'm compiling and commiting in minutes. I changed "void updateShear" to
> "Vector3r updateShear", to avoid computing shear displacement twice.
>
Great, thanks Bruno!

> (*) I used to use classIndex to check types, instead of dynamic_casts. Is
> it still possible? What is the best way in your opinion?
>
> Bruno
>
>
>
>
>
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