Testing of stiffened composite cylindrical shells in the postbuckling range until failure

The results of an experimental investigation of two stringer-stiffened shells and of two ring- and stringer-stiffened cylindrical shells made of carbon fabric reinforced plastic are presented. The specimens are tested until collapse by means of custom-made biaxial testing equipment that allows axial and torsion loading applied separately and in combination, using a position control mode. This apparatus includes a laser scanning system for the measurement in situ of the geometric imperfections, as well as of the progressive change in deformations. The experimental data acquired during the first nondestructive buckling tests and during the destructive failure tests clearly demonstrate the strength capacity of these structures to work in the postbuckling field, allowing for the further weight savings likely to be requested in the near future for the construction of aerospace structures. Indeed, the results show that the shells are able to sustain load in the postbuckling field without any damage, whereas the collapse, both under axial compression and under torsion, due to the failure of the stringers is sudden and destructive. The measured data can be used for the development and validation of analytical and numerical high-fidelity methods and, together to these validated analysis tools, to provide design criteria that are less conservative than those presented.