Analysis of bonded and fastened repairs by the p-version of the finite-element method

The development of efficient and reliable methods for the design and analysis of fastened structural connections and bonded joints is among the most important and most challenging problems in aerospace applications because these connections are common sites of failure initiation and there is a complicated nonlinear interaction between the fasteners and the connected plates. Realistic representations of fastened connections must account for the diameter of fastener holes, the stiffness of the fasteners, the effects of interference fitting or looseness of fit, contact between the fasteners and the connected plates, and yielding of the plates. Similarly, the treatment of bonded joints is complicated by the fact that bonded patches are typically composed of several thin layers of orthotropic material and the adhesive material may yield under load, requiring a nonlinear analysis. Consequently, the complexity of the models is such that it is difficult and time consuming to treat them using conventional finite-element or boundary-element procedures. Fortunately, these problems lend themselves to standardization in FEA-based handbook libraries. Structural connections can be described in a parametric form. Therefore, topologically similar families of connections need to be meshed only once. The FEA-based handbook library provides for the archival and recall of entries for analysis. Users need only enter the parameters. The finite-element mesh, being associative, is adjusted automatically. Therefore, users need not be concerned with meshing or other details of the analysis process. The finite-element solution and the computation of all data of interest are performed automatically and the results are displayed in tabular and graphical forms. Automatic quality control tests are performed and reported for purposes of documentation. There are provisions for the computation of margins of safety. The advanced FEA- based handbook library produces results of sufficient reliability to permit certification of repairs and joints based on computed information. This will be demonstrated by examples.