National Natural Science Foundation of China, No. 11372062, 2014.1-2016.12
As a dominating failure mechanism of large-diameter grid stiffened cylindrical shells, compression-induced buckling is known to be very sensitive to initial geometrical imperfections. It is a great challenge to develop a type of stiffened shells with high load-carrying capacity and low imperfection sensitivity for Chinese new-generation Launch Vehicles and future Heavy Lift Launch Vehicles. Recent research has shown that biological materials and many civil engineering structures such as the Eiffel Tower are composed of hierarchical sub/micro-structures and they all exhibit excellent tolerance of flaws. Inspired by these research findings, this application proposes a new structural concept for investigating multi-level grid stiffened shells that focuses on the characterization of the failure modes and failure strengths at different stiffener levels of structural hierarchy. We seek to use state-of-the-art numerical and experimental approaches to unveil the scientific facts underpinning the low imperfection-sensitivity of these multi-level grid stiffened shells. Based on this exploration, a novel optimization method is expected to be developed for directly identifying the most unfavorable imperfection among several base shapes of geometrical imperfection such as dimple-shape imperfection. With the proposed multi-level model and the multi-objective optimization approach, combined with plate homogenization method by Kalamkarov and proposed multiple smeared stiffener approach, we aim to deepen the understanding of the optimum design of this new type of stiffened shells and to obtain a couple of innovative and realizable launch vehicle designs by taking into account both load-carrying-capacity and imperfection-sensitivity objectives.