The imperfection sensitivity of axially compressed steel conical shells - Lower bound curve

摘要

This paper presents the numerical results centered on the buckling behavior of axially compressed imperfect conical shells. It was assumed that the cone model was made from mild steel. The perfect cone will be subjected to multiple imperfection approaches such as (i) eigenmode imperfection, (ii) single and multiple load indentation approaches, (iii) crack imperfection, and (iv) uneven axial length imperfection to study the reduction of buckling strength of the structure. As predicted, imperfection severely affected the buckling strength of conical shells, and the decrease in buckling strength could be seen to be heavily reliant on the imperfection approach. It is apparent that for axially compressed cones with radius-to-thickness ratio, r(1)/t = 25, uneven axial length imperfection was seen to produce the lowest buckling load, followed by eigenmode imperfection, crack imperfection, and load indentation for imperfection amplitude 0 A 1.68. Increasing the imperfection amplitude, A, beyond this level, i.e., A = 1.68, the highest reduction in buckling load was found to be eigenmode imperfection, followed by the uneven axial length, crack and load indentation. Furthermore, based on ECCS 2008 recommendation for imperfection tolerance, the lower bound curve, which can be used for design recommendation purposes, has been proposed for the worst imperfection approach case, i.e., uneven axial length and eigenmode imperfection for different conical shell geometry configurations. Finally, the proposed lower bound curve was compared with the plot of NASA SP-8019 recommended imperfection correlation factor for axially compressed cone. Results showed that the proposed lower bound curve for axially compressed conical shells with uneven axial length imperfection is notably higher than the NASA SP-8019 KDF by 7%, thus confirms the conservativeness of NASA SP-8019 KDF. However, axially compressed conical shells with eigenmode imperfection were seen to underestimate NASA's KDF by 55%, particularly for elastic buckling.