Surfaces are created from the element
faces of the underlying material. The discussion that follows assumes that the
surfaces will be defined in
Abaqus/CAE.
Restrictions on the types of surfaces that can be created in
Abaqus
are discussed in
Surface Definition;
please read them before beginning a contact simulation.
Surfaces on
continuum elements
For two- and three-dimensional solid continuum elements you specify which
regions of a part form the contact surface by selecting the regions of a part
instance in the viewport.
Surfaces on
structural, surface, and rigid elements
There are four ways to define surfaces on structural, surface, and rigid
elements: using single-sided surfaces, double-sided surfaces, edge-based
surfaces, and node-based surfaces.
Using single-sided surfaces, you specify which side of the element forms the
contact surface. The side in the direction of the positive element normal is
called SPOS, while the side in the direction of the negative element normal is
called SNEG, as shown in
Figure 1.
The connectivity of an element defines the positive element normal, as
discussed in
Using Shell Elements.
The positive element normals can be viewed in
Abaqus/CAE.
Double-sided contact surfaces are more general because both the
SPOS and SNEG faces
and all free edges are included automatically as part of the contact surface. Contact
can occur on either face or on the edges of the elements forming the double-sided
surface. For example, a secondary node can start on one side of a double-sided surface
and then travel around the perimeter to the other side during the course of an analysis.
Currently, double-sided surfaces can be defined only on three-dimensional shell,
membrane, surface, and rigid elements. In Abaqus/Explicit the general contact algorithm and self-contact in the contact pair algorithm enforce
contact on both sides of all shell, membrane, surface, and rigid surface facets, even if
they are defined as single-sided. Double-sided contact surfaces cannot be used with the
default contact formulation in Abaqus/Standard, but they can be used with certain optional contact formulations; see About Contact Pairs in Abaqus/Standard for more information.
Edge-based surfaces consider contact on the perimeter edges of the model.
They can be used to model contact on a shell edge, for example. Alternatively,
node-based surfaces, which define contact between a set of nodes and a surface,
can be used to achieve the same effect, as shown in
Figure 2.
Rigid
surfaces
Rigid surfaces are the surfaces of rigid bodies. They can be defined as an
analytical shape, or they can be based on the underlying surfaces of elements
associated with the rigid body.
Analytical rigid surfaces have three basic forms. In two dimensions the
specific form of an analytical rigid surface is a two-dimensional, segmented
rigid surface. The cross-section of the surface is defined in the
two-dimensional plane of the model using straight lines, circular arcs, and
parabolic arcs. The cross-section of a three-dimensional rigid surface is
defined in a user-specified plane in the same manner used for two-dimensional
surfaces. Then, this cross-section is swept around an axis to form a surface of
revolution or extruded along a vector to form a long three-dimensional surface
as shown in
Figure 3.
The benefit of analytical rigid surfaces is that they are defined by only a
small number of geometric points and are computationally efficient. However, in
three dimensions the range of shapes that can be created with them is limited.
Discretized rigid surfaces are based on the underlying elements that make up
a rigid body; thus, they can be more geometrically complex than analytical
rigid surfaces. Discretized rigid surfaces are defined in exactly the same
manner as surfaces on deformable bodies.