Vibration-correlation technique for predicting the compressive buckling load of cylindrical shells under combined loading

The feasibility of the Vibration Correlation Technique (VCT) to predict the compressive buckling load of cylindrical shells under combined loading was numerically assessed. For this purpose, bending, shear, and torsion were applied in various amplitudes either individually, or simultaneously, next to the main compressive load for 6 cylinders. Then, the robustness of VCT to predict the axial load level at which buckling occurred under combined loading was assessed based on the prediction accuracy with respect to the buckling axial load level obtained through non-linear analysis, as well as on the differences in accuracy with respect to the predictions for the pure compression load case. The numerical investigation revealed that the VCT predictions of the buckling axial load level were accurate for small degrees of additional load applied next to compression, with relative errors with respect to the non-linear buckling loads within 10%. This aspect was valid regardless of the load type, loading sequence, or whether the additional load was taken into account or not when determining the reference critical buckling load needed to perform VCT. Furthermore, the VCT predictions were better when the vibration response reflected a change in the axial load level alone (sequential load introduction), particularly for bending. When additional bending was applied next to compression, taking into account this load in determining the critical buckling load improved the axial buckling load estimation, while for shear the opposite was observed. On the other hand, for torsion-compression taking into account the torsion load when determining the critical buckling load provided better predictions for some cylinders, while for the others the opposite was observed.