The Behavior of Compressively Loaded Stiffener Runout Specimens – Part I: Experiments

Abstract

The development of the next generation of civil and military transport aircraft will inevitably see an increased use of advanced carbon fibre composite material in the primary structure if performance targets are to be met. One concern in this development is the vulnerability of co-cured and co-bonded stiffened structures to through-thickness stresses at the skin–stiffener interfaces, particularly in stiffener runout regions. These regions are a consequence of the requirement to terminate stiffeners at cutouts, rib intersections, or other structural features which interrupt the stiffener load path. This work presents the results of an experimental programme investigating the failure of thick-sectioned stiffener runout specimens loaded in uniaxial compression. For all tests, failure initiated at the edge of the runout and propagated across the skin–stiffener interface. It was found that the failure load of each specimen was greatly influenced by intentional changes in the geometric features of these specimens. High frictional forces at the edge of the runout were also deduced from a fractographic analysis, indicating a predominantly Mode II initial failure mode.