A Configuration-Space Interrogation Approach to the Understanding and Design of Critical Load-Bearing Structures Susceptible to Buckling

Duke University, Durham NC

Investigators

Abstract

Predicting the load that a structure can safely withstand before it collapses is challenging. During its useful life-time, a structure is expected to perform within an often severe, and changing environment, whether this is a solid-rocket booster during lift-off; a multi-story building during an earthquake; a grain silo during strong winds; an aircraft wing during turbulence; or an ocean submersible subject to great pressure at depth. The failure of slender cylindrical structures, in particular, is sensitively dependent on small changes in geometry, and when they do fail, usually due to buckling, it is often a sudden and catastrophic event. Due to their unpredictable behavior, they are typically over-designed. This award supports the development of an innovative approach to understanding the buckling of slender structures in general, and hollow cylindrical structures in particular. A more rational basis for assessing load-carrying capability, including appropriate safety factors, will allow more accurate predictions to be made concerning the anticipated useful lifetime of a given structure resulting in tremendous savings. This research is also important for optimizing component replacement, scheduling maintenance based on deteriorating performance, and minimizing material usage. Economic designs and the prevention of disaster are long-term benefits of the research. During the conduct of this research, graduate and undergraduate students will learn a variety of skills including structural testing, mathematical modeling, additive manufacturing, experimental design, and data analysis. Since hollow cylinders are widely used as containers, ranging from soda cans to pipelines to pressurized aircraft fuselages, this project has important impact on national defense and prosperity. Testing thin cylinders under axial load typically leads to large scatter in the measured buckling load. This has led engineers to rely on relatively conservative design guidelines based on empirical ?knockdown? factors. Rather than trying to predict the exact load at which a highly nonlinear structure will buckle, the major goal of the new approach is to assess the robustness of a structure to shocks or disturbances: a form of configuration-space interrogation. The identification of unstable equilibrium states, and their avoidance, is a key feature of the new stability criteria. 3D-printing will be used extensively. The geometric precision and versatility of 3D-printing is ideally suited to producing a range of high-resolution cylinders that will be thoroughly tested in the laboratory. Numerical simulations will also be conducted for verification purposes. The fundamental knowledge gained in this research will provide an important contribution to the understanding of structural stability and ultimately guide the design and use of critical load-bearing elements. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.