I am still having some trouble with the displacement solution of the UEL I have written, when compared to the displacement solution of an Abaqus standard element.
I noticed certain things if I ramp up the applied load, or applied the load instantaneously over 10 increments:
for the Abaqus standard element, it made no difference to the solution;
however, for the UEL, when the load was ramped, the incremental load (DU) was the value which one would expect the total load (U) to be. The total load compounded this, and is hence too large, and incorrect.
When the load is applied instantaneously to the UEL, the total load is 10 times the value it supposed to be.
I tried changing the RHS formulation, and hence, the residual, but this appears to have no effect on the displacement solution at all. Its a linear problem, of course.
Please advise on how to get my displacements to match the standard element.