Global/Local FEM-BEM stress analysis of damaged aircraft structures

In this paper a Hierarchical approach for the analysis of advanced aerospace structures is presented. The proposed Global/Local model uses two kind of numerical methods. The first step of the Hierarchical procedure is performed by the Finite Element code Patran/Nastran™, using a coarse mesh to study the global structure, then the local region is analyzed by using a Boundary Element code based on the multidomain anisotropic technique. This code accurately predicts stress concentrations at crack tips with a reduction of the modeling efforts and of the computational time. The Global/Local interface code implemented allows an intuitive extraction of the local region with a substantial reduction of the modeling time. The accuracy and the effectiveness of the model have been demonstrated analyzing classical stress concentration problems. Then the procedure has been used to analyze more complex structures among which a riveted patch repair, applied on a cracked panel, and a cracked graphite-epoxy curved panel with Z stiffeners and Z frames.