Experimental study of impact loading on negative stiffness structures

This work outlines the design of a drop testing apparatus and the use of the apparatus to perform impact tests on negative stiffness honeycomb structures. Negative stiffness beams are non-linear spring elements that can be used to absorb energy. When prefabricated negative stiffness beams are arranged together in a periodic pattern they create an energy absorbing honeycomb material that can recover from large deformations. Negative stiffness honeycombs have been shown to function similarly to regular honeycombs during quasi-static loading, but are largely untested for impact loading. Two types of honeycomb designs--referred to as vertical and horizontal arrays--have been designed and fabricated to experimentally determine their performance when subjected to impact loading. The performance of each array is compared using finite element models (FEM), quasi-static tests, and drop tests. A drop test apparatus is constructed to perform the impact testing, by measuring the acceleration profile of a mass released from variable drop heights. Results indicate that vertical and horizontal honeycombs reduce accelerations by at least 85 percent when compared to impact without the presence of a honeycomb.