Nondestructive shell-stability estimation by a combined-loading technique.

The variation of specimen lateral stiffness with compressive axial loading is studied experimentally, and it is demonstrated that buckling loads can be predicted for monocoque shells from such data. A study of the initial specimen geometry is presented, and an evaluation is made of its effect on the distribution of stiffness at zero axial load. When the lateral test force used to determine the stiffness is considered as a destabilizing load in combination with the axial compression, it is shown that critical values of the force can be estimated by the 'Southwell plot' procedure. These critical forces can be correlated with axial load and extrapolated to yield an accurate estimate of the buckling load.