I'm an electrical engineering student at the university of pittsburgh working on MEMS structural modeling. I'm currently trying to develop mass/stiffness matrices for a thin (constant thickness) shell/plate4-Node Element with x,y, and z degrees of freedom. From my research, it appears using the Plane stress theory, the x and y DOF are determined and then the z, and rotations about x and y are determined in a separate "bending" matrix. Thus the total matrix for the plate/shell is decoupled. When I attempt to add the two matrices together, my results are not consistent w/ a simple shell element in ANSYS. The results are in the same magnitude, but differe by as much as 50%.
Can anyone point me to a reference where I can move in the direction creating a coupled 3-DOF (x,y,z - rigid plate/shell) element stiffness and mass matrix.
Thanks very much,
Michael Bails University of Pittsburgh Department of Electrical Engineering