Modelling Rivets in the Finite Element Analysis

Riveting is a well established technology in the manufacturing of aeronautical structures as well as in the automotive industries. Despite its simplicity, the rivet presents a local stiffness that is not easy to properly model within a large finite element analysis. However, precision in the local stiffness evaluation is essential to perform any structural analysis when several rivet are applied in a joint structure. The result is that any rivet requires a local mesh refinement or, and this is the most common case, a drastic simplification of its structural modelling characteristics. In the present paper a new rivet element is introduced, able to precisely evaluate both local and overall stiffness of riveted joints; this finite element can be applied when dealing with 3D riveted shell structures. The modelling approach is similar to that, developed also by the author for spot welds. Of course, due to the different assemblage technology, the theoretical solutions are modified accordingly. The strategy leads to the substitution of the shell structure surrounding the rivet by an assembly of appropriate beams. In the overall the assembly presents the same stiffness of the region they substitute. The result is appealing: a rivet finite element that combines the precision in the simulation together with a very limited number of d.o.f.'s introduced by any rivet in the overall finite element structure.