MECHANICAL RESPONSE OF APPLYING DIFFERENT PARAMETERS ON NEGATIVE STIFFNESS HONEYCOMB STRUCTURE

Abstract

It has become apparent that negative stiffness behavior may have potential applications in vibration isolation mechanisms, vibro-acoustic dampening materials, and mechanical switches. Unlike traditional honeycombs, due to these properties, a negative honeycomb can absorb substantial amounts of mechanical energy whilst maintaining a stable stress. This thesis investigates the force threshold under displacement loading of three parameters applied on different models of negative-stiffness honeycomb (NSH) structures. The three parameters are material applied on the structure, honeycomb unit cell, and beam thickness of the negative honeycomb structure. Each part of this parameter is divided into three different variables. First, nylon 11, nylon 12 and nylon 6/6 which are widely used as polymer material were applied on the honeycomb model. Then, three different beam thickness of 6.35 mm, 12.7 mm and 19.05 mm were modeled and unit cell of 4, 5 and 7 numbers of arrangement were created using LS-Dyna software. Accordingly, 27 models were developed, and the three varied materials were assigned repeatably to each model and then force threshold were evaluated. The Finite element analysis (FEA) for formed model was validated and shows force value of 289 N with an error of 5% compared to the referenced model. In the 4- unit cell model, the highest force threshold of approximately 240 N was noticed during loading phase at the beam thickness of 19.05 mm for both nylon 11 and 12 material. While for the 5-unit cell honeycomb structure, was observed for nylon 6/6 material at beam thickness of 19.05 mm that was almost 1.2 times forces required for nylon 11 and 12 during first peak of loading and unloading phase. The results obtained confirm the negative stiffness behavior on the studied models and shows that the force threshold applied is reduced comparing to forces required in the conventional honeycombs models. Thus, it has the potential to be used for impact-sensitive applications such as bicycle seats and food packaging.