Post-buckling and collapse experiments of stiffened composite cylindrical shells subjected to axial loading and torque

Experimental data obtained from buckling and post-buckling tests performed until collapse on three stiffened composite cylindrical shells are described. The shells, different in the skin and in the stiffeners lay-up, were expressly designed for working in the post-buckling field. The outer and inner surfaces are scanned before the tests, in order to determine the initial geometric imperfections and the thickness variations. After that, the shells are tested using a position control mode until collapse, two of them under axial compression and one under torque. The diagrams of axial load versus displacement and of torsion versus rotation are recorded in real time during the tests. To monitor the first buckling load and the evolution of the buckling shape, five laser displacement sensors are employed. The test results show the strength capacity of these structures to work in the post-buckling range. Indeed neither failure mechanisms nor any other hazards are visible in the post-buckling range. On the other hand, the collapse, due to the failure of the stringers, is sudden and destructive.