Hello everybody,
I have programmed a UEL subroutine for a 3D cohesive element and I have a
problem (I think it would be the same with a 3D brick element).
When I do the validation test on a single element, the subroutine
converges if and only if I put initial boundary conditions on all nodes.
For example, imagine the bottom surface is fixed and the upper surface
is prescribed a displacement. If displacement is prescribed on the upper
nodes in the 2-direction during step 1, the displacement in the
1-direction on these nodes has to be constrained in the model data
(initial conditions). If this latter constraint is not specified, the
subroutine does not work.
With, conventional elements, these constraints are not necessary
I really do not understand why ?
Thank you for your assistance.