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double-sided, the positive or negative orientation of the contact normal
direction will be chosen such as to minimize (or avoid) penetrations for each
contact constraint. If either or both of the surfaces are single-sided, the pos-
itive or negative orientation of the contact normal direction will be deter-
mined from the single-sided surface normals rather than the relative
positions of the surfaces.
When the orientation of a contact surface is relevant to the contact for-
mulation, modelers must consider the following aspects for surfaces on struc-
tural (beam and shell), membrane, truss, or rigid elements:
(1) Adjacent surface faces must have consistent normal directions.
(2) The slave surface should be on the same side of the master surface as the
outward normal. If, in the initial configuration, the slave surface is on
the opposite side of the master surface as the outward normal, ABAQUS
[1.29] will detect overclosure of the surfaces and may have difficulty
finding an initial solution if the overclosure is severe. An improper spec-
ification of the outward normal will often cause an analysis to immedi-
ately fail to converge.
(3) Contact will be ignored with surface-to-surface discretization if single-
sided slave and master surfaces have normal directions that are in
approximately the same direction. It should be noted that discontinuous
contact surfaces are allowed in many cases, but the master surface for
finite-sliding, node-to-surface contact cannot be made up of two or
more disconnected regions (they must be continuous across element
edges in 3D models or across nodes in 2D models). ABAQUS [1.29]
cannot use 3D beams or trusses to form a master surface because the ele-
ments do not have enough information to create unique surface nor-
mals. However, these elements can be used to define a slave surface.
2D beams and trusses can be used to form both master and slave surfaces.
For small-sliding contact problems, the contact area is calculated in the
input file preprocessor from the undeformed shape of the model; thus, it
does not change throughout the analysis, and contact pressures for small-
sliding contact are calculated according to this invariant contact area.
This behavior is different from that in finite-sliding contact problems,
where the contact area and contact pressures are calculated according
to the deformed shape of the model.
5.2.2.4 Defining Contact with Contact Elements
As mentioned earlier, some contact problems cannot be modeled using gen-
eral contact and contact pair formulations. Therefore, ABAQUS [1.29]
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