Shock isolation using switchable stiffness

Abstract

This study investigates a novel stiffness control strategy applied to the problem of shock isolation. This is based on the principle that the stiffness and mass are the principal physical properties that control the passive system shock response. The problem of shock response control is divided in two stages. Firstly, the maximum response whilst a shock is applied is considered, and the effectiveness of a switchable isolation stiffness strategy is evaluated. This strategy aims to reduce the shock response by switching the stiffness to a low value during the shock input. Two different models are considered for the theoretical analysis, namely, a single mass supported by two elastic elements one of which can be disconnected, and a second model where the switchable element comprises a secondary mass-stiffness system. The performance of the two strategies is analyzed in terms of response parameters such as the absolute and relative displacement and absolute acceleration. The single degree-of-freedom system is considered as a benchmark for comparison. The issue of residual vibration suppression is then presented. For the latter a different switchable stiffness strategy is identified, and the analysis is mainly concerned with the energy dissipation mechanism used to suppress residual vibration. As in the first stage of shock isolation, two models are considered. Optimum configurations and stiffness changes are identified for both the shock response reduction and the decay of the residual vibration. The effect of viscous damping is subsequently incorporated. The practical implementation and experimental validation is then presented and a experimental system is developed. It is based on a conceptual model comprising a magnetic suspension element that is able to change its effective stiffness by altering the magnetic force. This novel configuration has the advantages of achieving a high stiffness change in a very short amount of time and with very low damping, which is required to validate the theoretical studies. The design and properties of the model are discussed and then both stiffness strategies are implemented. This model is used to show the feasibility and evaluate the isolation performance of the different switchable stiffness strategies and the issues and limitations of the implementation.

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ORCID for Neil Ferguson: orcid.org/0000-0001-5955-7477

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