Geometric nonlinearity

I am trying to write my own code for geometrically nonlinear analysis of mixed structures (cables, trusses, beams...). I would like to have it as general as possible ie. applicable also to 2D and 3D solids. I am trying to follow nonincremental Newton Raphson procedure from Ansys theory manual, but my computation are not converging.. Can I kindly ask you for advice ?

Here is my flow:

=== Linear analysis ===

(1) inv Kt *F = du

resluts are correct comparing to Ansys

=== Nonlinear analysis ===

while (F_ext - F_int) < 1e-3

(2) u = u +du

(3) computing new transformation matrix T and new tangent stiffness matrix Kt ( = Ke + Kg) in global coordinate system based on coordinates updated by du

(4) computing nodal vector of internal forces using only elastic stiffness matrix from (3): Ke * u = F_int

(5) computing residulas: F = F_ext - F_int

(6) computing increment of deformations using tangent stiffness from (3) and residual forces from (5): inv Kt * F = du

(7) go to (2)

end

Is my flow correct ? Can you plese advise me how to improve it, or make it correct and general ?