Developing the Next Generation Shell Buckling Design Factors and Technologies

Abstract

Directorate. The SBKF project has the current goal of developing less-conservative, robust shell buckling design factors (a.k.a. knockdown factors) and design and analysis technologies for light-weight stiffened metallic launch vehicle (LV) structures. Preliminary design studies indicate that implementation of these new knockdown factors can enable significant reductions in mass and mass-growth in these vehicles and can help mitigate some of NASA's LV development and performance risks. In particular, it is expected that the results from this project will help reduce the reliance on testing, provide high-fidelity estimates of structural performance, reliability, robustness, and enable increased payload capability. The SBKF project objectives and approach used to develop and validate new design technologies are presented, and provide a glimpse into the future of design of the next generation of buckling-critical launch vehicle structures.

The Geometric Role of Precisely Engineered Imperfections on the Critical Buckling Load of Spherical Elastic Shells

“…Our study is well aligned with efforts currently underway by NASA and others interested in large shell structures to replace the old empirical knockdown factors employed in design codes by an approach that (i) first, measures the topographic distributions of imperfections, (ii) then, predicts buckling loads from the measured data, and (iii) finally, determines the corresponding knockdown factors [39,40]. In contrast to a statistical approach that starts from measuring uncontrollable imperfections, here we have precisely and systematically controlled a single imperfection and were able to predict the associated knockdown factors.…”

Technical Brief: Knockdown Factor for the Buckling of Spherical Shells Containing Large-Amplitude Geometric Defects

“…Nonetheless, despite significant theoretical and computational efforts in understanding imperfection sensitivity, practical designs of curved shells have traditionally made use of empirical knockdown factors [11,12]. In contrast to this approach, efforts currently underway by NASA and others in the aerospace industry aim at developing deterministic design guidelines based on manufacturing-specific imperfection distribution [13][14][15].…”

Stacking sequence influence on imperfection sensitivity of cylindrical composite shells under axial compression

“…The shell buckling phenomena has been subject of research for many years and is currently addressed within the EU project New Robust DESIgn Guideline for Imperfection Sensitive COmposite Launcher Structures (DESICOS) [1] and within the NASA Shell Buckling Knock Down Factor (SKBF) project [2]. Due to the imperfection sensitivity of these structures, deriving an appropriate mathematical description of the shell buckling problem, which allows a reliable and robust buckling load prediction, is a demanding task.…”