convergence issues, elements deforming excessively

[sergini]

All, I am running an analysis that includes pore fluid flow. That means that initial stress conditions are effective stresses. If I run the analysis assuming elastic behaviour is fine. If I employ the mohr-coulomb plasticty model behaviour I got convergence issues it said that some element are deforming excessively. This happens in the early stages of the analysis and I checked all boundary conditions and they look fine. Any clue? Do I missing something?
Rgds, Sergini

 

[PamCrash]

Units ok ?

 

[mrgoldthorpe]

Are you applying dead load(s) or prescribed displacement(s)? The former can give rise to such problems as yours in elastic-plastic analyses. If you can, consider applying the latter instead of the former.

Try reducing the magnitude of load in your initial step, and/or try reducing the initial increment size and maximum increment size in the step. With regard to the latter, ABAQUS will increase the size of successive increments if convergence of previous increments is satisfactory. Unfortunately, this sometimes leads to excessive deformation in subsequent increments as the extent of plastic deformation increases in the model: leading to convergence difficulties, increment size cut-backs and so on.