Escaping the Ashby limit for mechanical damping/stiffness trade-off using a constrained high internal friction interfacial layer

Abstract

The development of new materials with reduced noise and vibration levels is an active area of research due to concerns in various aspects of environmental noise pollution and its effects on health. Excessive vibrations also reduce the service live of the structures and limit the fields of their utilization. In oscillations, the viscoelastic moduli of a material are complex and it is their loss part – the product of the stiffness part and loss tangent – that is commonly viewed as a figure of merit in noise and vibration damping applications. The stiffness modulus and loss tangent are usually mutually exclusive properties so it is a technological challenge to develop materials that simultaneously combine high stiffness and high loss. Here we achieve this rare balance of properties by filling a solid polymer matrix with rigid inorganic spheres coated by a sub-micron layer of a viscoelastic material with a high level of internal friction. We demonstrate that this combination can be experimentally realised and that the analytically predicted behaviour is closely reproduced, thereby escaping the often termed ‘Ashby’ limit for mechanical stiffness/damping trade-off and offering a new route for manufacturing advanced composite structures with markedly reduced noise and vibration levels.

Novel phase separated multi-phase materials combining high viscoelastic loss and high stiffness

“…In the current study we have used the conclusions of this previous work and have used the 'nlayered' micromechanical model to produce numerical predictions of the storage shear modulus and tan of appropriate idealised composite microstructures in an effort to gain insight into the relationship between the morphology and mechanical behaviour of our samples. This strategy is strengthened by another recent study [13], where we showed excellent predictions of the experimental behaviour using the same Barium titanate beads used here, but spray coated with a different viscoelastic polymer and then incorporated in the same polystyrene matrix [13]. In that study, very close agreement was found between the experimental measurements and the numerical micromechanical predictions, giving us confidence to follow the same strategy with the materials in this study.…”

“…But most importantly, as is found in this current work, on incorporation of a rigid particle (either spheres or fibres) a thin layer of the SIS copolymer is seen to form on the surface of the particles, see Fig. 1, effectively producing a coated particle as investigated and described in our previous work [13].…”

“…These results mirrored those for the laminate beams, but offered a material in which the amplified lossy behaviour was isotropic and which also could be processed into a complex final shape using, for example, injection moulding. In a recent study [13] , we proved that such materials could be experimentally realised by embedding coated glass spheres into a polystyrene matrix, and that the loss amplification effects produced were in close agreement to those predicted micromechanically.…”

“…The spherical glass spheres, grade UB-02M, were obtained from Unitika, Ltd. and were selected for the narrowness of its size distribution, but mainly to retain consistency with previous studies where they were used in a coated form [13]. The beads were made from a Barium titanate glass with a density of 4.2 gcm -3 and had an average diameter, measured using a standard particle sizer, of 42m.…”

“…This is a reasonable assumption, as a previous study by Gusev [12] showed that introducing a lossy component for the bulk modulus for coated spheres gave almost indistinguishable results from those obtained using a purely elastic form. This strategy can be considered validated by the success of the predictions for coated Barium titanate beads described in [13]. samples of the pure SIS rubber and unfilled PS/SIS blends [16].…”