Essentially, the spot weld is modeled using a thin elastic layer. The stiffness of the elastic layer is separated into a normal stiffness, kn, and a shear stiffness, ks. The stiffness can be given by the user. The default is that it is automatically computed using the following expressions.

Here, Eequ and νequ are the equivalent Young’s modulus and Poisson’s ratio values respectively. The values are taken on the destination side. Lcohe is a parameter called the cohesion length. It represents the thickness of the virtual thin elastic layer, and should this be of the order of the distance between the welded plates. The default value is 1% of the nugget diameter.

For each integration point, a search is made to find the corresponding location on the source boundary. Thus, a displacement difference can be found:

Using the normal to the shell on the destination side, n, the displacement difference can be separated in normal and tangential parts: