Failure of thick-skinned stiffener runout sections loaded in uniaxial compression

Recent efforts towards the development of the next generation of large civi l and military transport aircraft within the European community have provid ed new impetus for investigating the potential use of composite material in the primary structure. One concern in this development is the vulnerabilit y of co-cured stiffened structures to through-thickness stresses at the ski n-stiffener interfaces particularly in stiffener runout regions. These regi ons are an inevitable consequence of the requirement to terminate stiffener s at cutouts, rib intersections or other structural features which interrup t the stiffener load path. In this respect, thickerskinned components are m ore vulnerable than thin-skinned ones. This work presents an experimental a nd numerical study of the failure of thick-sectioned stiffener runout speci mens loaded in uniaxial compression. The experiments revealed that failure was initiated at the edge of the runout and propagated across the skin-stif fener interface. High frictional forces at the edge of the runout were also deduced from a fractographic analysis and it is postulated that these forc es may enhance the fracture toughness of the specimens. Finite element anal ysis using an efficient thick-shell element and the Virtual Crack Closure T echnique was able to qualitatively predict the crack growth characteristics for each specimen. (C) 2001 Elsevier Science Ltd. All rights reserved.