Civil Engineering Reference
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nodes, and modelers must choose which surface will be the slave and which
will be the master. The larger of the two surfaces should act as the master
surface. If the surfaces are of comparable size, the surface on the stiffer body
should act as the master surface. If the surfaces are of comparable size and
stiffness, the surface with the coarser mesh should act as the master surface.
For node-to-surface contact, it is possible for master surface nodes to
penetrate the slave surface without resistance. This penetration tends to
occur if the master surface is more refined than the slave surface or a large
contact pressure develops between soft bodies. Refining the slave surface
mesh often minimizes the penetration of the master surface nodes. If the
refinement technique does not work or is not practical, a symmetric
master-slave method can be used if both surfaces are element-based surfaces
with deformable or deformable-made-rigid parent elements. To use this
method, modelers can define two contact pairs using the same two surfaces,
but they have to switch the roles of master and slave surfaces for the two
contact pairs. Using symmetric master-slave contact pairs can lead to over-
constraint problems when very stiff or “hard” contact conditions are
enforced. For softened contact conditions, use of symmetric master-slave
contact pairs will cause deviations from the specified pressure-versus-
overclosure behavior, because both contact pairs contribute to the overall
interface stress without accounting for one another. Likewise, use of sym-
metric master-slave contact pairs will cause deviations from the friction
model if an optional shear stress limit is specified, because the contact stresses
observed by each contact pair will be approximately one-half of the total
interface stress. Similarly, it can be difficult to interpret the results at the
interface for symmetric master-slave contact pairs. In this case, both surfaces
at the interface act as slave surfaces, so each has contact constraint values asso-
ciated with it. The constraint values that represent contact pressures are not
independent of each other.
ABAQUS [1.29] requires master contact surfaces to be single-sided for
node-to-surface contact and for some surface-to-surface contact formula-
tions. This requires that modelers consider the proper orientation for master
surfaces defined on elements, such as shells and membranes, that have pos-
itive and negative directions. For node-to-surface contact, the orientation of
slave surface normals is irrelevant, but for surface-to-surface contact, the ori-
entation of single-sided slave surfaces is taken into consideration. Double-
sided element-based surfaces are allowed for the default surface-to-surface
contact formulations, although they are not always appropriate for cases
with deep initial penetrations. If the master and slave surfaces are both
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