In-vacuo adaptive beam element for vibration control

This paper proposes a novel in-vacuo adaptive beam element for vibration control, which, in this study, is employed as an adaptive tuneable vibration absorber. The element is formed by a composite beam with a core of structured fabrics wrapped in a deflated plastic bag skin. The fabrics consist of 3D-printed chain mails of hollowed truss-like particles. A base post is connected at the middle section of the composite beam, such that its flexural vibration is controlled by a flapping fundamental natural mode whose natural frequency can be varied by changing the vacuum level in the bag. The dynamics of this arrangement replicates that of a suspended mass-spring-damper system and, thus, can be suitably used as a tuneable vibration absorber. The study considers in-vacuo composite beams with one or two overlapping chain mails made with cubic, spherical-octahedral, octahedral hollowed truss-like particles. To start with, the dynamic response of these structures is analysed with respect to dynamic stiffness frequency response functions measured with a six-point bending setup. The dynamic response of the centrally pinned in-vacuo adaptive beam element is then investigated considering the vibration transmissibility and base impedance frequency response functions. Finally, the tuning features and vibration control effects of the adaptive beam element are assessed by fitting it at the free termination of a clamped beam in order to control the resonant response of a target flexural mode. Overall, the experimental results have shown that the fundamental natural frequency of the proposed in-vacuo adaptive beam element can be swiftly lifted or lowered by modulating the vacuum level in the bag encasing the structured fabrics. Indicatively, the working centre frequency of the resulting absorber depends on the number of strips piled in the vacuum bag, which defines the thickness, and thus the reference bending stiffness, of the in-vacuo composite beam. Also, the working frequency bandwidth of the in-vacuo adaptive beam element mostly depends on the geometry, the material and the finishing of the chain mail particles. In fact, these properties infer on the number, the type (between convex or non-convex surfaces), the area and the friction coefficient of the contacts that develop between neighbouring particles of the mails and thus determine the range of bending stiffness that can be achieved by a given vacuum range in the deflated bag.