The traditional way of modeling spot welds involves matching the meshes of different parts at the spot weld connection points, which introduces meshing difficulties and often requires parts to be meshed manually. In addition, this approach does not take into account the effects of the spot weld radius, and it underestimates the strength of the spot weld connection when the radius of the spot weld is the same or lesser order of magnitude than the mesh size.
The spot weld feature, based on the internal multipoint constraint (MPC) approach, offers a robust alternative to the traditional method. This feature allows you to easily model thin sheet components that are connected with spot welds, rivets, or fasteners. The spot weld can be located anywhere between the parts that are to be connected, independent of the mesh and the node locations. The figure below shows an example of the spot weld configuration. Each spot weld set connects two or more surfaces.
There are several advantages to using this mesh independent spot weld capability:
Parts can be meshed independently.
A basic spot weld set can be easily defined by specifying two surfaces to be connected and a single node called the spot weld node near the surfaces. The spot weld node determines the location of the spot weld.
This approach takes into account effects of the spot weld radius input by the user. The program creates multipoint constraint equations (MPCs) internally through two contact pair definitions, one on each spot weld surface. The internal constraint equations (force-distributed constraints) couple the motion of the surface nodes to the motion of the spot weld node in an average sense.
The spot weld can be rigid (default) or deformable. To specify a deformable spot weld, you simply define a deformable beam element type prior to creating the spot weld.
Two configurations are available for spot welds.
Pilot node configuration (default)
Node-to-surface configuration (NTOS)
By default, each new spot weld set created by SWGEN consists of a beam element and two MPC contact pairs (which are force-distributed constraints).
If the ICTY field of an
SWGEN command is set to NTOS, the spot weld set
created by the SWGEN command consists of a beam/joint element and two
node-to-surface MPC contact pairs. In general, node-to-surface configuration of spot welds
is useful for the generation of multiple spot welds with fewer contact pair definitions.
Multiple surfaces can be added to the spot weld by providing a component group name in the
NCM1 field. No SWADD command is needed. The
NTOS approach can also be used to define single spot weld set.
The following spot weld topics are available: