Dynamic simulations with nonlinear material into Explicit

Hi all,

 I am new in the Forum, and I am looking for some informations regarding how to simulate nonlinear material in explicit.

I am tryng to analyse the behaviour of a roller rolling on the sand (or mud), but the results I get with a basic elasto-plastic material are not very accurate, expecially because I cannot set the tension allowed in the sand to be zero.

Other ways to input nonlinearity in Explicit are always refused by ABAQUS. Is there any way to get something more accurate?