Hi guys,

I'm working on an ABAQUS extension/plug-in of a sort and I'd like to replicate results for a single 4-node plane stress element produced by the ABAQUS incremental/nonlinear static solver.

I assumed the relationship is:
t[K] {Δx} = t+Δt {P} - t{F}

This is how I went to obtain these values:
t [K] - element stiffness - by using *ELEMENT MATRIX OUTPUT
Δx - displacement increment - difference in displacements of the nodes for two consecutive increments
t+Δt {P} - applied load - CF history output of all nodes
t {F} - internal nodal forces - NFORC history output of all nodes

When I sub these values in, LHS does not match RHS. There could be two possible reasons: 1) the relationship used in ABAQUS is different, and 2) the values I extracted are not the ones that ABAQUS uses.

Do you guys see what's wrong in here? I'd really appreciate any thoughts and ideas as I got quite exhausted trying to figure it out and my thoughts started going in circles.

Cheers,
mkajtaz