DBEM and FEM analysis on non-linear multiple crack propagation in an aeronautic doubler-skin assembly

The performance of a riveted patch repair, applied on a cracked panel, is simulated by using both a commercially available Boundary Element code (BEASY) and a Finite Element code (ANSYS). A two-dimensional stress analysis on a single-sided repaired configuration is performed by both methodologies; consequently, the occurrence of out-of-plane bending and its effect on the through-thickness SIF (Stress Intensity Factor) variation is neglected. The connection between the two layers (patch and panel) is realised by 32 rivets, with through-cracks initiated on the most loaded holes. Special elements are used to model the crack: discontinuous elements in the DBEM (Dual Boundary Element Method) approach or quarter point elements in the FEM (Finite Element Method) approach. Different loading configurations are considered depending on the presence of a biaxial or uniaxial remote load and the non linear hole/rivet contact is simulated by gap elements. The most stressed skin holes are highlighted, and the effect of a through crack from such holes is analysed in terms of SIFs and stress redistribution. The accuracy in SIFs assessment by DBEM and FEM and the respective computational and pre-processing efforts are determined. Such a two-dimensional analysis allows us a straightforward pre-processing phase, and very short run times are needed. A peculiar arrangement of the pin configuration in the DBEM analysis allows us to take into account the real in-plane plate stiffness and the transversal pin stiffness, even in a 2D analysis (this is straightforward by using FEM).