Nondestructive buckling test for an integrally stiffened structure

Abstract

The determination of the buckling loads on an integrally stiffened, integral wing fuel tank is described. A simplified scale test model of the relevant wing structure was built and tested under a matrix of wing bending and internal pressure loading. The local buckling load combinations were predicted using the modified Southwelltype force-stiffness method. It was confirmed that for this case the method covers the possibility of late mode changes near the buckling load better than the Southwell plot does. Hence, it was possible to obtain repeated buckling load combinations on the same specimen and thus actual buckling never occurred. At the end of this series of tests, a wing bending load was applied at zero pressure until general buckling occurred, at which point the entire test specimen failed. The problem was complicated by the fact that the wing chord was relatively large, thereby imposing plane strain and biaxial stress condition on the wing skin. The results of this work were used to construct curves of buckling stresses as functions of internal pressure for use in stress analysis and design of the wing.