Comparative Numerical Investigation of Eigen-Worst, Spla and 4mpla in Cfrp, GFRP and Aluminium Cylindrical Shells Under Axial Compression

Thin-walled cylindrical shells under axial compression exhibit pronounced sensitivity to geometric imperfections, which can significantly diminish their buckling strength. The present study examines this imperfection-sensitive behaviour in CFRP and GFRP composite cylindrical shells, as well as L165 aluminium-alloy cylindrical shells, by means of finite element simulations. Three imperfection modelling strategies are considered, namely the Eigen-Worst approach, the Single Perturbation Load Approach (SPLA), and the four-point Multi-Perturbation Load Approach (4MPLA). Numerical results are assessed against experimental data reported in the literature, and satisfactory agreement is obtained, particularly for the SPLA-based predictions. The comparison indicates that eigenmode-based modelling leads to conservative estimates that depend strongly on the selected mode, whereas SPLA provides smoother and more stable lower-bound knockdown factors. The inclusion of 4MPLA produces a further reduction in knockdown factor, showing that the interaction of multiple local dimples generates a more critical imperfection state than a single perturbation load. Among the materials investigated, the GFRP shell is found to be the most sensitive to the multi-perturbation configuration. Overall, the study establishes a comparative basis for evaluating imperfection modelling strategies and supports the choice of suitable lower-bound approaches for the practical buckling assessment of cylindrical shells.