Gradual degradation of a thin-walled aluminum adhesive joint with omega cross section under bending

Abstract The aim of the study was to examine deformation and degradation of a longeron fragment or a crossbeam in aircraft fuselage. The study included: (1) performing new laboratory investigations and (2) developing a corresponding numerical model of the structural element's behavior. Laboratory tests, i.e. controlled deformation by 3 PB (3-point bending) until bending collapse, were performed on specimens with a thin-walled omega cross section consisting of 2 aluminum parts: a roll-formed omega shape and a flat strip. Both parts were continuously bonded with 4 different types of structural adhesives, Fig. 1. Results of the laboratory tests and numerical analysis provided comprehensive knowledge of the structural element's behavior over the full range of loading conditions, starting from the elastic response, through the initialization of bending collapse and degradation processes, local folding and cracking, up to the final phase of bending collapse. A Finite Element Analysis (FEA) model of the structural element's deformation including adhesive layer damage and ductile damage in the aluminum parts of the test specimen was elaborated. The model allowed for the description of the longeron's gradual degradation until the final failure including: (1) plastic collapse mechanisms with cracking inside the aluminum parts and (2) delamination of the adhesive layers under 3 PB deformation. The agreement between the experimental and FEA results confirms that the numerical model of the investigated structural element was designed based on correct assumptions.