Problem description:

A thin  rectangular sheet with a central perforation subject
to tensile  loading. Due  to mirror  symmetry one quarter of
the structure  is presented,  and  internal  boundaries  are
restrained in x and y directions respectively.

The uniform  tensile loading  (40 N/mm**2) is applied to the
bottom edge of the structure.
The dimensions of whole structure are as follows:

     Length = 240mm; width = 180mm;
     radius of central opening r = 30mm.


Material properties:

     Young's modulus = 2.07E+5 N/mm**2;
     Poisson's ratio = 0.3.

The problem  may be solved both  in a plane  stress or plane
strain formulation.
