Design and evaluation of negative stiffness honeycombs for recoverable shock isolation
Negative stiffness elements are proven mechanisms for shock isolation. The work presented in this thesis investigates the behavior of negative stiffness beams when arranged in a honeycomb configuration. Regular honeycombs consisting of cells such as hexagonal, square, and triangular absorb energy by virtue of plastic deformation which is unrecoverable. The major goal of this research is to investigate the implementation of negative stiffness honeycombs as recoverable shock isolation so as to better the performance of regular honeycombs.To effectively model the honeycomb behavior, analytical expressions that define negative stiffness beam behavior are established and finite element analysis (FEA) is used to validate them. Further, the behavior of negative stiffness beams when arranged in rows and columns of a honeycomb is analyzed using FEA. Based on these findings, a procedure for the optimization of negative stiffness honeycombs for increased energy absorption at a desired force threshold is developed. The optimization procedure is used to predict trends in the behavior of negative stiffness beams when its design parameters are varied and these trends are compared to those observed in regular honeycombs. Additionally, experimental evaluations of negative stiffness honeycombs under quasi-static loading are carried out using prototypes built in nylon 11 material manufactured by selective laser sintering (SLS). Energy absorption calculations conclude that optimization of negative stiffness honeycombs can yield energy absorption levels comparable to regular honeycombs. A procedure for dynamic testing of negative stiffness honeycombs is discussed. Results from dynamic impact testing of negative stiffness honeycombs reveal excellent shock absorption characteristics. FE models are developed for static and dynamic loading and the results show strong correlation with experiments. Further, temperature dependency of nylon 11 is investigated using impact tests on honeycomb prototypes. Finally, example applications utilizing negative stiffness honeycombs are discussed and recommendations are made for their refinement.