User element, access non-zero-boundary-displacement, UL is zero

[patagr]

Hello,

I use feap 8.4 and I am trying to create a user element (elmt**.f) for finite elasticity.

Imagine a rectangular region for a static plane stress analysis. The left and the bottom edge are set to zero-displacement with EBOU. A node on the top right is set to non-zero-displacement with CBOU and CDIS.

There are no body forces and there is no surface load. So the residual consists of the stress divergence term only.

At the beginning of the analysis UL(*,*,*) is zero. So the cauchy-stresses and finally the stress divergence term is zero. -> no iterations.

What do I need to do additionally to access the non-zero-displacement boundary?

My isw.eq.3 is based on:
FEAPHOME/elements/solid2d/fld2d1.f ('Purpose:  2-D Finite Deformation Elasticity Routine')
FEAPHOME/elements/material/finite/modlfd.f (called in fld2d1.f)
FEAPHOME/elements/material/finite/stnh3f.f (neo hookean model, called in modlfd.f)

I took my isw.eq.1 from another user element.

Thanks in advance!

[Prof. R.L. Taylor]

Feap uses the tangent matrix to impose nonzero displacement increments from the current state.  At the start this is from the reference configuration, so tangent will be identical to small strain case.  Afte, it will differ.  This ensures all displacement increments use same tangent.

[patagr]

I see. Thank you very much