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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 pecimens 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 mperfections, 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

The results obtained on two predamaged closed boxes composed of four graphite-epoxy curved stiffened panels are presented. One panel of each box is predamaged, using Teflon inserts between three stringers and the skin to reproduce skin-stringer disbonding. The boxes are tested under axial compression and torque, applied individually and in combination, both statically and cyclically. The tests allow the investigation of the effect of static and cyclic postbuckling combined loads in terms of structural behaviors, of collapse modalities and of damage propagation. The boxes do not suffer any loss of structural performances or any predamage propagation for combined loading under small compression and torsion up to 275% of the buckling torque, which corresponds to 85% of the collapse torque