Vibration response of tunable structured fabrics with applications

Structured fabrics are fabrics realized by rigid mechanical truss structures interwoven to obtain flexible garments such as chain mail armors. Although fabrics’ properties are usually fixed, recent publications have demonstrated the tuneability of structured fabrics. It has been shown that vacuum pressure applied between two layers of 3D printed chain mails causes jamming of the chain mails and an increase in the bending modulus up to twenty-five times. The increase in the effective bending modulus is due partly to the compressive frictional forces and partly to the geometrical interlocking of the complex shapes. In this paper we investigate the vibration response of tunable structured fabrics when subject to variables vacuum pressures. The investigation is focused on the variation of the vibration characteristic and of the dynamical properties with the vacuum pressure, and the geometry and dimension of the truss-structure elements. The chain mails are fabricated with different geometries (spheres, tetrahedra and cubes) using 3D-printing technology. The material is then wrapped in a bag whose vacuum pressure is tuned with a vacuum pump such that the stiffness and damping properties of the resultant smart structure can be suitably tuned. To start with, the paper presents static and dynamic 3-point bending tests which show that the bending stiffness and fundamental resonance frequency of the specimens can be increased significantly by augmenting the void in the bags. The damping effect does not depend substantially on the vacuum level but varies significantly with respect to the geometry of the constitutive elements of the fabrics. Possible applications include the realization of lightweight adaptive and semiactive vibration mitigation devices. Hence, the paper shows that this smart structure can be conveniently used to develop a tunable vibration absorber, which can be used to control the time-harmonic response of a mechanical system subject to variable tonal excitation.