I have a VERY thin circular membrane with an out-of-plane force applied
at the center. The edges of the membrane are clamped. I am using the
SHELL181 membrane-only option, but the model will not converge. Why?

Please see the attached ANSYS 11.0 input file for the required procedure.
Essentially, the membrane needs to be stiffened enough to be able to
support the force. Otherwise, it just ignores it. By stretching the perimeter
radially outward a little, the membrane is sufficiently stiffened. NLGEOM,ON
includes stress stiffening (SSTIF,ON), but that is not enough by itself, since
you need the membrane stretched to get the first solution. In the last load
step, the perimeter of the membrane is returned to its proper location.


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