Theory for the Membrane Interface
Introduction
A membrane is similar to a shell, but it has only translational degrees of freedom and the strain is constant in the thickness direction.
The thickness of the membrane is
d
, which can vary over the element. The displacements are interpolated by Lagrange or Serendipity shape functions.
A 2D axisymmetric membrane is similar to the 3D membrane and it has a nonzero circumferential strain in the out-of-plane direction.