I wrote a UEL for one element and compared to a reference UEL (FEM), where the results agreed satisfactorily, except the reaction force. The stress, strain, strain energy all were pretty accurate.
I am unable to understand this, how does Abaqus calculate reaction force?
I am simply restraining the element in the bottom(two nodes) and applying displacement(incrementally) at the top(two nodes).
As far as I know, the STIFFNESS matrix is used to calculate reaction force in these cases, the stiffness values are quite similar in my UEL and the FEM UEL. Also if this was the case, the other parameters wouldn't have had the same values.
This is probably leading to convergence issues when I am using my UEL for more than one element, where the solutions cannot even converge for the first increment.
Would be grateful if anybody could help me figure this out.