Spot Welds
Add one or more Spot Welds nodes to model sets of spot welds. A single Spot Welds node can accommodate any number of spot welds, as long as they share the same properties. The spot weld locations are entered as a list of coordinate triplets, and are independent of geometrical points or mesh nodes.
The connection is elastic. The spring stiffness can either be viewed as a pure penalty formulation of a constraint, or be directly related to the physical flexibility of the connection. Since the connection is distributed across the nugget area, the sport weld also possess bending and torsional stiffness.
When one or more Spot Welds nodes are active in the model, four entries will be added to the list of predefined plots:
A Spot Weld Forces plot group, containing the normal and shear forces at each spot weld as arrows, and a label showing the identity number of each weld.
A Spot Weld Forces evaluation group, containing a table of the normal and shear forces of all spot welds.
A Nugget Location plot group, containing a surface plot showing the nugget locations, a point plot at Gauss points showing the location of the nuggets on the destination boundary, and a mesh plot.
A Connected Region Indicator plot group, containing a surface plot showing the areas on the destination surface where the spot welds are active. If there are other connection features in the Shell interface, all connection indicators appear in the same plots.
Note that if you change the number of spot welds in your model, and compute new results, then you must delete the Spot Weld Forces plots and evaluation groups, and add them again from the list of predefined plots.
Boundary Selection
Select the boundaries that form one side of the set of spot welds.
Boundary Selection, Destination
Select the boundaries that form the other side of the set of spot welds.
The equations for the connection are set up on the destination side. If there is a difference in mesh density, select the side with the finer mesh as destination.
Nugget Location
In the table, enter the coordinates of the centers of the spot welds. The coordinates do not have to be exactly on the shell surface. Each given spot weld location will be projected onto the nearest point on the destination boundary.
Use the Add button () to add a row to the table, the Delete button () to delete a row in the table, or the Clear Table button () to clear the whole table.
Use the Load from file button () and the Save to file button () to load and store the list of nugget locations using a text file with space-separated columns.
The sides of the shells (top or bottom) that are to be connected must be known. The information is used for two purposes: to connect to the correct set of displacements, and to compute the distance, including the shell thickness and offset.
Select Connected locationAutomatic or Manual. In the automatic mode, the two sides of the shells that are found to be closest to each other are connected. If you want to make another choice, or the if the automatic search for some reason does not give the intended result, select Manual.
In manual mode, the Source and Destination lists are shown. Select Top surface or Bottom surface from both lists.
Nugget Properties
Enter the Nugget diameter, dnug.
Select the Nugget stiffnessFrom material or User defined.
When data is taken From material, the elastic material properties (E, ν) on the destination side are used.
Enter the Cohesive thickness, Lcohe. This is a distance in the direction perpendicular to the plate used to compute the stiffness of the connection. Its value should be of the order of the spacing between the welded plates. The default value is one percent of the nugget diameter, dnug/100.
The normal and shear stiffnesses (per reference area) are then computed as
The total stiffness of a spot weld is obtained by multiplying by the cross-section area of the nugget, as defined by its diameter.
For User defined nugget stiffness, enter values or expressions for the Normal stiffness, kn, and Shear stiffness, ks. These are the total stiffnesses of a single spot weld (SI unit N/m).
Quadrature Settings
The stiffness that each spot weld generates between the two connected boundaries is computed using numerical integration. If the size of the mesh element is large relative to the nugget diameter, a high integration order may be needed to get an accurate estimate of the integral. Using very high integration orders together with a large number of spot welds can have a negative impact on the solution time.
When Use automatic quadrature settings is selected, the integration order is set to 8, which means that there are 5-by-5 integration points in a quadrilateral element.
Clear Use automatic quadrature settings to manually enter an integration order. The maximum value is 30, which means 16-by-16 points in a quadrilateral element.
Advanced
To display this section, click the Show More Options button () and select Advanced Physics Options in the Show More Options dialog.
Select the Search methodClosest point or Manual to specify what should happen if an evaluation point in the destination boundary is mapped outside the source boundary.
The Closest point method is the default and most robust search method. The closest point in the source selection is used by the mapping operator, even if that point is far away from the destination point. This method is not as efficient as the Manual method.
The Manual method is an alternative search method that is computationally efficient, but its robustness is determined by the curvature of the boundaries, the Search distance, and the Extrapolation tolerance. Specify the maximum search distance between the source and destination boundaries and the extrapolation tolerance.
See Advanced Settings for Nonlocal Couplings in the COMSOL Multiphysics Reference Manual for more information.
Location in User Interface
Context Menus
Ribbon
Physics tab with Shell selected: