Design And Mechanical Behavior Of Sleevetype Negative Stiffness Structures

Negative stiffness structures have unique deformation mechanisms and mechanical responses such as reusability,snap-through behaviors,multi-stable characteristics.Thus,they are completely different from common lightweight structures.And because of these characteristics,this type of structure has broad application prospects in buffering devices for impacting and damping devices in vibration.However,restricted by structural characteristics and deformation mechanism,the stiffness and carrying capacity of traditional negative stiffness structures are much lower than common lightweight structures,which greatly limits their application.In order to solve this problem,this work proposes a new negative stiffness mechanism,and based on this,the following studies are carried out:First,single-material sleeve-type negative stiffness structures were designed.Based on the classical elastic theory,the stress and strain distribution of the structures were analyzed.On this basis,the design criteria for this type of structure was established.Sleeve-type negative stiffness unit cells were prepared using polymer materials and highperformance titanium alloys as base materials.Cyclic experiments and finite element methods were used to study the structures,and the influence of design parameters on the structure was discussed.The experimental results show that the single-material sleevetype negative structure inherits many advantages of the traditional negative stiffness structures,such as reusability,multi-stable characteristics,etc.while having much higher stiffness and carrying capacity than those of traditional negative stiffness structures.Secondly,under the guidance of the "collaborative design" idea of composite materials and structures,a composite sleeve-type negative stiffness structure was designed.The structure is composed of soft and hard materials.Based on the classical elastic theory,the distribution of stress and strain in the structure was analyzed,which provides a theoretical tool for the design of the structure.Based on the finite element method,the deformation shape and strain distribution of the structure were studied,and the influence of the stiffness ratio of soft and hard materials on the structure was discussed.Besides,the loading and unloading laws of the structure were also studied based on cyclic experiments.Experiments based on different loading rates were conducted to investigate the sensitivity of the speed to the structure.The results show that the structure has excellent reusability characteristics and good energy dissipation capability,but the energy dissipation capability will be affected by the loading speed.The above two parts of the research are mainly for the sleeve-type negative stiffness unit cells.In order to analyze the structures and systems composed of multiple cells and springs,this work proposed a multilinear model.Based on this model,theoretical research is carried out on the parallel problem of a single sleeve-type unit cell and a spring,the Abstract parallel problem of multiple sleeve-type negative-stiffness cells,and the complex series connection of negative-stiffness cells and springs.The concept of phase-difference parallel connection was proposed,and the energy dissipation capacity of the structure and the specific damping coefficient of the structure were studied based on the multilinear model and integral method.It is found that the phase-difference series-parallel connection can greatly improve the specific damping coefficient of the structure.Finally,based on experiments,the problem of parallel connection of multiple cells and the problem of series connection between cells and springs were studied,and the theoretical results of the multilinear model were verified.The nonlinear effect of the sleeve-type negative stiffness metamaterial was discussed,and the damping performance of the structure under dynamic load was preliminarily studied.The experimental results show that the multilinear model can well solve the series-parallel problem of the sleevetype negative stiffness structure.The structure composed of the cells with the phasedifference parallel connection has a higher specific damping coefficient under dynamic loading.The damping performance can quickly dissipate the mechanical energy in the structure.