Shape and loading imperfection sensitivity of the vibration-correlation technique for buckling analysis of cylindrical shells

Abstract

A numerical investigation regarding the feasibility of the Vibration Correla- tion Technique (VCT) to predict the buckling load of cylindrical shells under compression, with multiple amplitudes of shape and loading imperfections was performed. The capability of VCT to give reliable buckling load predictions using load steps before and after local buckling occurred was also assessed, us- ing two different VCT procedures and buckling analyses. It was found that the buckling load predictions using VCT are generally insensitive to shape and loading imperfections, but that certain imperfections might give uncon- servative predictions, behaviour which generally can be identified with ease. Increasing the imperfection amplitudes increased the number of secondary buckling events, which in turn decreased the robustness of the VCT to pre- dict the global buckling load when load steps before the local buckling were used. Predicting the global buckling load using load steps after local buckling occurred seemed possible, but might provide unconservative results. In this case, using a 4th order VCT procedure and taking into account out-of-plane imperfections in the buckling analysis significantly increased the reliability of the VCT predictions. Nevertheless, while the numerical results clearly sug- gest that such predictions would be possible, giving the increased difficulty in tracking vibration modes after local buckling occurred, an experimental vali- dation could difficult as well. Furthermore, considering that a single structure with various amplitudes of the same imperfections was used in this study, the results using load levels beyond the one where local buckling occurs might be structure specific and could only be validated through experimental testing.