A methodology for developing high damping materials with application to noise reduction of railway track

For application in damping treatments, elastomeric materials should have a high<br/>damping loss factor, but this is inevitably linked to a strong temperature-dependence<br/>of the dynamic properties. A methodology is developed that allows a material to be formulated<br/>for a particular damping application where temperature-dependence has to be<br/>taken into account. The methodology is applied to the case of a tuned absorber system<br/>used for damping the vibration of a railway track. This is required to be effective over a<br/>temperature range -20°C to 40°C.<br/><br/>To investigate the effect of the temperature on the performance of a rail damper,<br/>a simple Timoshenko beam model of the track vibration is used, to which are added<br/>single-frequency and dual-frequency tuned absorbers. The results show that a high noise<br/>reduction can be achieved for the optimum stiffness, provided that the loss factor is<br/>between about 0.25 and 0.4.<br/><br/>In order to study the generic effects of high damping versus constant stiffness, the<br/>time-temperature superposition principle is used to convert frequency-dependence to<br/>temperature-dependence for a notional material with constant loss factor. This is used in<br/>the prediction of decay rates and thereby noise reduction. In addition, a weighted noise<br/>reduction is studied by using measured rail temperature distributions. This temperatureweighted<br/>noise reduction allows a single number measure of performance to be obtained<br/>which can be used to assess various elastomeric materials in order to determine the optimum<br/>material for a given situation.<br/><br/>Two types of viscoelastic material, butyl and EPDM rubbers with various amount<br/>of fillers and plasticisers are investigated. The properties of both rubbers have been<br/>measured over the range of temperatures for frequencies 300-3000 Hz. For this a test<br/>rig had to be modified. For butyl, the best combination of filler and plasticiser gives<br/>temperature weighted noise reductions up to 5.9 dB(A). Butyl rubber is suitable for use<br/>in the rail absorber giving high noise reductions between 0°C and 40°C. The best EPDM<br/>compound gives a temperature-weighted noise reduction up to 6.2 dB(A). Comparing<br/>these two rubbers, EPDM is more suitable for low temperatures below 10°C and butyl is<br/>more suitable for higher temperatures above 10°C.

Name dc:type.qualificationname

Ph.D.

Level dc:type.qualificationlevel

doctoral

Grantor dc:publisher.institution

University of Southampton

Year dc:date.issued

2009

Author dc:creator

• Ahmad, Nazirah

Advisor dc:contributor.advisor

• Thompson, David