Fracture mechanics based assessment of manufacturing defects laying at the edge of CFRP-metal bondlines

This study presents a simplified approach for the evaluation of the bond line load capacity of CFRP-metal hybrid structural parts, bearing manufacturing defects. The proposed approach overcomes the need of modeling debonding with the use of advanced non-linear FEM, and relies on the post-processing of the stress and strain fields developed at the free edges of the hybrid material (critical locations in the presence of manufacturing defects), with the use of interfacial fracture mechanics. First, the mathematics, related to the analytical calculation of the bi-material fracture toughness, is presented and applied to a simple CFRP-metal geometry. Corresponding FE simulations are performed and the J-integral is employed for the numerical calculation of the SERR magnitude of different defect sizes. In the following, a simplified calculation of the SERR magnitude that sources from FE results and implemented in geometries modeled by shell finite elements that typically require advanced modeling techniques, is provided for the simulation of the de-bonding process.