A novel cylindrical negative stiffness structure for shock isolation

Analytical and Experimental Investigation of Buckled Beams as Negative Stiffness Elements for Passive Vibration and Shock Isolation Systems

Journal of Vibration and Acoustics ◽

10.1115/1.4026888 ◽

2014 ◽

Vol 136 (3) ◽

Cited By ~ 87

Author(s):

Benjamin A. Fulcher ◽

David W. Shahan ◽

Michael R. Haberman ◽

Carolyn Conner Seepersad ◽

Preston S. Wilson

Keyword(s):

Resonance Frequency ◽

Vibration Isolation ◽

Negative Stiffness ◽

Peak Acceleration ◽

Single Beam ◽

Buckled Beams ◽

Buckled Beam ◽

Double Beam ◽

Shock Isolation ◽

Isolation Systems

The behavior of a buckled beam mechanism, which exhibits both bistability and negative stiffness, is investigated for the purposes of passive shock and vibration isolation. The vibration and shock isolation systems investigated in this research include linear, positive stiffness springs in parallel with the transverse motion of buckled beams, resulting in quasizero stiffness behavior. For vibration isolation systems, quasizero stiffness lowers the resonance frequency of the system, thereby reducing its transmissibility at frequencies greater than resonance. For shock isolation systems, quasizero stiffness provides constant-force shock isolation at tailored force levels, thereby enabling increased capacity for absorbing shock energy relative to a comparable positive stiffness system. Single- and double-beam configurations that exhibit first-mode buckling are utilized for vibration isolation, and a single beam that exhibits first- and third-mode buckling is used for shock isolation. For all cases, the static and dynamic behavior of each configuration is modeled analytically. The models are then used to design prototype vibration and shock isolation systems that are fabricated using selective laser sintering (SLS). The dynamic behavior of the systems in response to base excitations is determined experimentally, and the results are compared to model-based predictions. The vibration isolation prototypes display isolation levels that are tunable by varying the axial compression of the beams. Double-beam systems are shown to provide greater reductions in resonance frequency than single-beam systems for comparable levels of axial compression. However, low-frequency isolation capabilities are sensitive to the high levels of precision required to obtain low levels of system stiffness. The shock isolation prototype provides isolation at prespecified threshold levels of force or acceleration. In the prototype system, an input shock with a peak acceleration of approximately 7 g is reduced to a peak acceleration of the isolated mass of approximately 1 g. High levels of negative acceleration are observed in models and prototype systems when the buckled beam snaps back to its original position; however, models indicate that large negative accelerations can be mitigated using one-way dampers.

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Negative stiffness honeycombs for recoverable shock isolation

Rapid Prototyping Journal ◽

10.1108/rpj-12-2014-0182 ◽

2015 ◽

Vol 21 (2) ◽

pp. 193-200 ◽

Cited By ~ 96

Author(s):

Dixon M Correa ◽

Timothy Klatt ◽

Sergio Cortes ◽

Michael Haberman ◽

Desiderio Kovar ◽

...

Keyword(s):

Energy Absorption ◽

High Energy ◽

Negative Stiffness ◽

Static Displacement ◽

Content Type ◽

Beam Geometry ◽

Displacement Behavior ◽

Shock Isolation ◽

Energy Absorbing ◽

Force Displacement

Purpose – The purpose of this paper is to study the behavior of negative stiffness beams when arranged in a honeycomb configuration and to compare the energy absorption capacity of these negative stiffness honeycombs with regular honeycombs of equivalent relative densities. Design/methodology/approach – A negative stiffness honeycomb is fabricated in nylon 11 using selective laser sintering. Its force-displacement behavior is simulated with finite element analysis and experimentally evaluated under quasi-static displacement loading. Similarly, a hexagonal honeycomb of equivalent relative density is also fabricated and tested. The energy absorbed for both specimens is computed from the resulting force-displacement curves. The beam geometry of the negative stiffness honeycomb is optimized for maximum energy absorption per unit mass of material. Findings – Negative stiffness honeycombs exhibit relatively large positive stiffness, followed by a region of plateau stress as the cell walls buckle, similar to regular hexagonal honeycombs, but unlike regular honeycombs, they demonstrate full recovery after compression. Representative specimens are found to absorb about 65 per cent of the energy incident on them. Optimizing the negative stiffness beam geometry can result in energy-absorbing capacities comparable to regular honeycombs of similar relative densities. Research limitations/implications – The honeycombs were subject to quasi-static displacement loading. To study shock isolation under impact loads, force-controlled loading is desirable. However, the energy absorption performance of the negative stiffness honeycombs is expected to improve under force-controlled conditions. Additional experimentation is needed to investigate the rate sensitivity of the force-displacement behavior of the negative stiffness honeycombs, and specimens with various geometries should be investigated. Originality/value – The findings of this study indicate that recoverable energy absorption is possible using negative stiffness honeycombs without sacrificing the high energy-absorbing capacity of regular honeycombs. The honeycombs can find usefulness in a number of unique applications requiring recoverable shock isolation, such as bumpers, helmets and other personal protection devices. A patent application has been filed for the negative stiffness honeycomb design.

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A Novel Shock Absorber with the Preload and Global Negative Stiffness for Effective Shock Isolation

Shock and Vibration ◽

10.1155/2021/8823422 ◽

2021 ◽

Vol 2021 ◽

pp. 1-15

Author(s):

Zecui Zeng ◽

Lei Zhang ◽

Ming Yan

Keyword(s):

Permanent Magnet ◽

Shock Absorber ◽

Jacobian Matrix ◽

Relative Displacement ◽

Negative Stiffness ◽

The Novel ◽

Shock Test ◽

Linear Spring ◽

Shock Isolation ◽

Isolation Performance

A novel shock absorber with the preload structure and global negative stiffness is proposed for the shock isolation of sensitive systems. The novel shock absorber is composed of a linear spring and permanent magnet sets. The preload force and negative stiffness region are related to the attractive force between permanent magnet sets. The aim of this paper is to investigate the shock isolation performance of the novel shock absorber. Firstly, a static analysis of the novel shock absorber is carried out. Secondly, the motion stability of the NSA is analyzed by the Jacobian Matrix and the shock response is calculated numerically compared with the conventional preload structures. Finally, the shock test of the novel shock absorber is completed to verify the above results. It is found that the novel shock absorber could be advantageous in improving shock isolation in terms of relative displacement and absolute acceleration compared with conventional preload structures.

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