Buckling Knockdown Factor Estimation of Externally Pressurized Cylindrical Shells

Thin cylindrical shells under compressive loads typically experience failure through buckling. The buckling phenomenon in these structures often demonstrates a notable disparity between theoretical predictions and experimental outcomes. In the design of such structures, the theoretically determined critical load undergoes a reduction through a factor known as the Buckling Knockdown Factor (KDF). Traditionally, KDF has been empirically derived, and conservative lower bounds are established in industry standards. Recognizing the importance of minimizing structural mass, recent literature has presented promising results for estimating KDF using numerical methods in the context of cylinders under axial compression. This paper addresses the novel challenge of estimating KDF for cylinders subjected to external pressure using numerical techniques. A comprehensive survey of various methods for KDF estimation is conducted, and the Single Perturbation Load Analysis (SPLA) method, a deterministic lower-bound approach, is employed to determine the KDF. The investigation delves into the selection of imperfection shapes for SPLA under external pressure loading, considering two worst-case imperfection shapes: dimple and longitudinal dent. The findings suggest that SPLA can serve as an effective tool for estimating KDF under external pressure loading. Both the imperfection shapes yield similar KDF estimates, and the collapse behavior at the critical load is comparable. Importantly, the numerically estimated KDF is found to be less conservative than the industry standard KDF, indicating the potential for designing lighter structures.