Oasys LS-DYNA Environment 8.1 VOLUME 3 ... - Oasys Software

Oasys LS-DYNA Environment: User Guide (Version 8.1)
of freedom are affected - slave nodes are effectively "pinned" to the master surface. Type 2
surfaces work by a kinematic constraint method: see the "Errors and Warnings" section below.
Any slave nodes that are initially far from the master segments will not be constrained. Slave
nodes that are near a master segment but are slightly offset will be constrained, but the offset can
lead to rotational constraints that cause erroneous results.
Tied surfaces involving nodes that are constrained in other ways or are offset from the master
segments should be of type o2. This type uses a penalty method that does not require nodes to
be unconstrained or to lie exactly on master segments.
SLIDING WITH VOIDS
Type 3: *CONTACT_SURFACE_TO_SURFACE
Type a3: *CONTACT_AUTOMATIC_SURFACE_TO_SURFACE
Type m3: *CONTACT_FORMING_SURFACE_TO_SURFACE
This type of surface is widely used to represent contact between components in a model.
Compression can be carried but not tension - the two components can separate. Sliding can be
resisted by friction.
On initialisation, the master node nearest to each slave node is found, and the master segments
attached to that node will be the first to be checked for contact. The process is repeated for the
master nodes and slave segments. Thereafter, sliding may mean that nodes move from one
segment to another. In type 3, this process is tracked using mesh connectivity: instead of
checking all segments for contact, only those segments attached to nodes of the previously
contacted segment will be checked. As a consequence, contact cannot be tracked across free
edges. Examples are given in the "Errors and Warnings" section below. Note that the search
method changes to “bucket sort” (see below) if SHLTHK on *CONTROL_CONTACT is nonzero
- see below. If type a3 (automatic surface to surface) is specified, the bucket sort method is
always used.
Once the contacted segments have been found for each node, the amount of penetration of the
slave node into the master segment is calculated and resisted by a penalty stiffness. The process
is repeated for the master nodes and slave segments. The stiffness calculation is described below.
Because the treatment is symmetric, it does not matter which surface is defined as the master and
which as the slave. It is possible for nodes to be part of several different contact surfaces.
Initial gaps between the slaves and masters are allowed but not necessary. If any nodes are
initially penetrating they will be moved back to the surface and a message will be printed in the
.OTF and .LOG files. This check can be omitted by setting the flag on Control Card 9, Column
25, to 1. In this case initial penetrations will lead to contact forces being developed on the first
timestep.
Type m3 surfaces are for use in metalforming simulation. They allow negative surface offsets to
be specified so that the same mesh geometry can be used for both the punch and the die. If the
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