Abaqus UMAT convergence

Hello,

I've got a problem getting my simulations in ABAQUS to converge.

I am using a UMAT routine to define a nonlinear material with an 
exponential strain stress relation. When imposing displacements the 
analysis converges rapidly, however, when imposing a concentrated load 
the simulation does not complete. I have checked my DDSDDE matrix and I 
believe it is correct.

Has anybody has similar problems, and if so, how did you solve them?

Many regards,
Diego

--
Diego d'Aulignac

ICIST
Departamento de Engenharia Civil - Instituto Superior Técnico
Av. Rovisco Pais
1049-001 Lisboa
Portugal

email: diego at civil ist utl pt
http://www.civil.ist.utl.pt/~diego/