Multi-level experimental and numerical analysis of composite stiffener debonding. Part 1: Non-specific specimen level

A multi-level analysis of skin/stiffener debonding is used for the fuselage design of future aircraft during postbuckling. The specimens composed of a laminate (the skin) to which an over-thickness (the flange) had been added were subjected to four-point bending, which led to interface failure between the flange and the skin. These tests were performed with several configurations and parameters, such as the orientation of the plies located at the interface, temperature (−50, 20 and 70 °C), ageing and manufacturing mode: co-cured or co-bonded. The flange shape (tapered or not) and thickness were also considered. Test data are presented and analyzed and critical configurations are identified. Finite element models were developed and the flange debonding loads computed, firstly by use of cohesive models and then through a fracture mechanics approach (Virtual Crack Closure Technique). In both cases, the Benzeggagh–Kenane criterion was selected and proved its efficiency but the fracture mechanics approach was an order of magnitude less time consuming, which will enable future modelling to include larger sizes.