Keywords: polymeric materials, damping elements, granular material, railroad vibration and noise reduction, hydrostatic pressure, thermoplastic polyurethane, frequency dependence.

This paper presents newly developed adaptive viscoelastic damping elements for the rolling noise reduction on rails. Adaptive viscoelastic damping elements are composed of carbon, glass or basalt fibres textile tubes filled with pressurized granulated polymeric materials. Granular material with properly selected multimodal particle size distribution acts as a pressurizing agent. At the same time the generated hydrostatic pressure changes frequency dependence of the granular material bulk properties. By modifying material bulk properties we can adaptively modify damping characteristics of the developed damping elements and utilize the full damping potential of a selected material.

The working concept of these dampers is demonstrated on thermoplastic polyurethane (TPU). It was found that: (i) By increasing the internal pressure of a damper from 0.1 MPa to 200 MPa the frequency at which the material exhibits its maximal damping properties is shifted from 37 kHz, at P = 0.1 MPa, to 235 Hz at P = 200 MPa, (ii) by increasing inherent hydrostatic pressure from 0.1 MPa to 200 MPa it is possible to increases stiffness of a damper up to 3.5 times, and its damping properties up to 5.5 times.

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