> > Doesn't the problem with different plasticity condition come into play > > only if you store shear force instead of strain? That would break for > > non-linear elasticity...? > Not sure it makes a difference. How do you define the plastic strain in > your case? I guess it uses plastic = total - elastic, with elastic = > some sort of ftmax/ks (remember... ;)). > Now, what if you cannot write elastic=ftmax/ks due to non linearity?
I don't store plastic strain at all (for shear plasticity, at least). At each step: 1. normal strain εN and stress σN are evaluated; 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.*** * For total strain, you just use that value; for incremental, you add current incremental to the previous value. ** by moving the equilibrium position, for total formulation; for incremental, cummulative strain value would be set. *** radial stress return; if stress return were not radial, one would have to iterate to find suitable combination of σN, |σT| to satisfy plasticity condition, as it is usually done in implicit scehemes. I didn't say anything about computing elastic energy... that would need some more thought. > 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. Cheers, v. _______________________________________________ Mailing list: https://launchpad.net/~yade-users Post to : [email protected] Unsubscribe : https://launchpad.net/~yade-users More help : https://help.launchpad.net/ListHelp
