Lower dimension structural elements such as trusses, beams, and membranes can be embedded into a solid domain by adding an Embedded Reinforcement multiphysics coupling. This modeling technique is intended for efficient modeling of thin structures in solids, where it is unfeasible or not necessary to resolve the geometry of the thin structure. Some typical use cases include:
When modeling embedded structures, it is sometimes easier to form the geometries of the coupled interfaces from an assembly. In the finalization step of the geometry sequence, you should select Form an assembly in the
Action list. This will also put less restrictions on the mesh of the respective geometry. If
Form Union is selected in the
Action list, the same mesh will be shared by both interfaces; which has to respect and resolve the geometry of the embedded structure.
Many quantities used by the connection, such as the spring stiffness and constitutive models, are most naturally represented in the local coordinate system of the embedded structure. For beam and membranes, the multiphysics coupling picks up the local coordinate system defined by the physics interface. However in the Truss or Wire interfaces, only the direction of the local edge tangent tle is defined. For the multiphysics coupling, two transverse direction are also needed when using a spring connection. Thus, the multiphysics coupling defines a local coordinate system by assuming that
tle is the normal to a plane. The actual directions of the two in-plane tangents are not important, and it is assumed that the first tangent points in the global
z direction. Hence, the first transverse direction is
where ez is the base vector that points in the global
z direction. Since no distinction is made between
t1 and
t2, only a single transverse spring constant,
kt, has to be entered when defining the spring stiffness matrix.
The slip is defined using a local constitutive model. This local model adds a set of internal degrees-of-freedom that are solved for and stored in the model at each Gauss point of the embedded structure. Typically, these internal variables include the relevant components of the slip vector ul,p, the accumulated slip
upe, and the friction dissipation density
Wp. The last variable is only added if the
Calculate dissipated energy check box is selected in the
Energy Dissipation section. The internal variables used by the
Embedded Reinforcement multiphysics coupling are shown as separate fields under
Dependent Variables node in the solver sequence.
The resistance to slide in the bond slip model is determined by the cohesion c, which can be a function of any variable or field present in the model; by adding a generic expression to the initial cohesion
c0. A built-in hardening model with respect to
upe can be also be added, in which case
c =
c0+
ch, where
ch describes some hardening function.
When adjusting the settings of the solver sequence for a model that includes an Embedded Reinforcement multiphysics coupling, make sure that the dependent variables of the coupled interfaces are solved in the same group. Also, note that the fields related to the bond slip model should be included in the same solver group as well. This is only a potential issue if a segregated solver is used, and it is handled automatically by the default solver suggestion.