In RFEM 6 it is possible to define multilayer surface structures with the help of the “Multilayer Surfaces” add-on. Hence, if you have activated the add-on in the model’s Base Data, it is possible to define layer structures of any material model. You can also combine material models of, for example, isotropic and orthotropic materials.
With the orthotropic elastic-plastic material model, you can calculate solids with plastic material properties in RFEM 5 and evaluate them according to the Tsai‑Wu failure criterion. The Tsai-Wu criterion is named for Stephen W. Tsai and Edward M. Wu, who published it in 1971 for plane stress states.
In RFEM, orthotropic plastic analyses using the Tsai‑Wu plasticity criterion have been possible for quite some time now. The hardening modulus Ep,x or Ep,y can be used to consider the hardening of the material during the iterative calculation.
Composite beams in a three-dimensional analysis are usually connected with orthotropic plates. In that case, the longitudinal direction of the plate stiffness is defined by a main beam and the transverse direction by an orthotropic plate. The stiffness of the plate in the longitudinal direction is set almost to zero. This article explains the determination of stiffnesses in the orthotropic plate.
In the "Edit Surface" dialog box, there is a new tab titled "Modify Stiffness" for the "Standard" and "Without Tension" surface types. Here, you can modify the elements of a stiffness matrix by defining the factors in the same way as in the case of orthotropic surfaces.
The form-finding process in RFEM seeks an equilibrium state where the defined prestress of membranes and the prestress or length changes of cable elements with boundary reactions are in equilibrium. For this, the program provides the option to define an isotropic or an orthotropic prestress state for membranes.