Engineers frequently face a critical selection decision between materials with high structural stiffness and materials with superior damping capabilities. Existing materials cannot provide both capabilities simultaneously. This award supports fundamental research to break this tradeoff by designing negative stiffness (NS) metamaterials. These materials gain their properties from their internal structure, which includes micro-scale structures that snap back and forth to absorb energy - a phenomenon called negative stiffness. Novel top-down design strategies developed in this project will allow engineers to quickly identify the material designs that meet performance goals as closely as possible. Negative stiffness metamaterials will benefit a variety of applications of great interest to society, such as stiff, low-vibration wind turbine blades and rotors and sonar mounts for submarines. The research involves graduate and undergraduate students, educational outreach activities, and a minority-serving institution, which will help broaden the participation of underrepresented groups and positively impact engineering education.
The research team will design these materials with a novel, top-down design exploration strategy for quickly and efficiently back-propagating application-specific, system-level performance requirements to the characteristics of the micro-scale material structure. This top-down strategy contrasts with trial-and-error, bottom-up strategies that cycle through multiple material structures in search of satisfactory system-level performance. The top-down design exploration strategy utilizes Bayesian network classifiers for mapping structure-property relationships at each level of the multi-level design problem in such a way that the maps can be intersected across levels to identify good multi-level designs and also efficiently guide the search for better designs. The design exploration strategy is coupled with three levels of material models, ranging from (a) the micro-scale level on which the geometry and fabrication route for the snap-through inclusions must be designed to provide negative stiffness behavior to (b) the meso-scale level on which the distribution of inclusions in a ductile matrix must be designed to provide targeted effective material properties to (c) the macro-scale level of a component, which must be designed along with the metamaterial to provide targeted structural stiffness and damping. Materials design and modeling efforts will be validated by additively manufacturing micro-scale inclusions using microstereolithography, embedding them in a matrix material, and testing the resulting composite to determine the overall dynamic structural stiffness and loss characteristics. A collaboration with an industrial partner will pave the way for applications of the NS metamaterials in challenging military and commercial applications.