When modeling contact solids, you should keep in mind that each connecting side surface between the contact surfaces is to be modeled as a simple surface with four boundary lines.
The FE mesh cannot be generated if this modeling rule is not considered. In that case, the program displays the following error message: "Side surface [Surface No.] does not have four boundary curves".
The contact solid shown in Figure 1 has contact surfaces F5 and F6 and side surfaces F1 to F4. Side surfaces F1 to F3 each have four boundary lines. Side surface F4 has six boundary lines (Lines 1 through 6) and thus does not correspond to the modeling rule, so the error message is displayed.
Lines 2 and 3, as well as 5 and 6, can now each be merged into one line, so that side surface F4 only consists of four boundary lines (Figure 2).
If it is impossible to merge the lines because, for example, other elements are connected, side surface F4 would have to be divided into several partial surfaces, each consisting of only four boundary lines. In Figure 3, side surface F4 has been divided into partial surfaces F4 and F7, making it possible to generate the FE mesh.
