Effect of Pressure on Damping Properties of Granular Polymeric Materials

Abstract

Reduction of noise and vibration coming from the rail transport activities is an important objective of the environmental policy of the European Union, due to its impact on human and animal health. It has been identified that one of the major sources of noise and vibration in rail transport is from the interaction between the wheel and the rail, the so called rolling noise. One way to mitigate this noise is to attach polymeric damping elements to the rail. By modifying bulk properties of polymeric material we can modify its damping characteristics. In this chapter we demonstrated on the example of thermoplastic polyurethane (TPU) the effect of inherent hydrostatic pressure on the time- and frequency-dependent behavior of polymers. For the selected TPU material we found that increasing hydrostatic pressure from 1 to 2000 bar shifts frequency at which material exhibits its maximal damping properties (G″max) from 37 kHz to 235 Hz. It was also found that change of pressure changes values of storage modulus G′ up to 3.5 times (depending on the frequency), while the values of loss modulus G″ are changed up to 5.5 times. Using this property of polymeric materials we developed new generation damping elements composed of glass fiber textile tubes filled with pressurized granulated polymeric materials. Granular material with properly selected multimodal particle size distribution acts as 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 modify damping characteristics of the new generation damping elements. Applying these damping elements to the rail can substantially reduce vibration amplitudes as well as sound pressure levels, thus reducing exposure of human and animal to noise and vibration.