Methods for Global and Local FEM Analysis of Riveted Joint on the Example of the PZL M28 Skytruck Aircraft

The paper considers some aspects of FEM modeling of riveted joints with application of shell elements and submodeling technique. Presented works were carried out within Eureka project No. E!3496 called IMPERJA. The goal of the IMPERJA project is to increase the fatigue life of riveted joints. The project assumed FEM modeling of the operating aircraft's structure at three different complexity levels, namely considering the complete structure, a structural detail and a single riveted joint. The paper presents analyses of various rivet models and calculations of a structure and a riveted joint.

In the first part examples of various rivet models were presented and usefulness of them was discussed. Influence of the following simplification was analyzed; • neglecting of rivets in a model (elements are jointed continuously) • rivet as a rigid element (MPC) • neglecting of contact phenomenon • neglecting of secondary bending. The basis of the analysis was the asymmetric butt joint model with 14 rivets. The model which took into account secondary bending and contact phenomenon was analyzed as well.

In the second part, the example of analysis of riveted joint on a lower skin of the PZL M28 Skytruck aircraft wing was presented. A submodeling technique was used there. At first, part of the wing model, was built. It includes 7 ribs and 6 bulkheads between them. Boundary conditions were taken on a basis of operation data. Presence of rivets was neglected. The Linear material model was used. The purpose of this calculation was to gain accurate boundary conditions for the model of riveted joint on the middle rib. Next a shell model of chosen area was build. Boundary conditions were set on a basis of result from previous analysis. Because of large stiffness difference between part models (part of wing and riveted joint) forces, instead of displacements, were used, as boundary conditions. The nonlinear model of material was used. A contact effect, secondary bending and residual stresses were taken into account. Results from this analysis are planned to be used as boundary conditions in a calculation of single rivet with solid detailed model. The presented method allows analyzing phenomena that appear around a rivet in a real structure, during operation. Analyses were performed with MSC PATRAN and NASTRAN software.