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

Abstract

For application in damping treatments, elastomeric materials should have a high
damping loss factor, but this is inevitably linked to a strong temperature-dependence
of the dynamic properties. A methodology is developed that allows a material to be formulated
for a particular damping application where temperature-dependence has to be
taken into account. The methodology is applied to the case of a tuned absorber system
used for damping the vibration of a railway track. This is required to be effective over a
temperature range -20°C to 40°C.

To investigate the effect of the temperature on the performance of a rail damper,
a simple Timoshenko beam model of the track vibration is used, to which are added
single-frequency and dual-frequency tuned absorbers. The results show that a high noise
reduction can be achieved for the optimum stiffness, provided that the loss factor is
between about 0.25 and 0.4.

In order to study the generic effects of high damping versus constant stiffness, the
time-temperature superposition principle is used to convert frequency-dependence to
temperature-dependence for a notional material with constant loss factor. This is used in
the prediction of decay rates and thereby noise reduction. In addition, a weighted noise
reduction is studied by using measured rail temperature distributions. This temperatureweighted
noise reduction allows a single number measure of performance to be obtained
which can be used to assess various elastomeric materials in order to determine the optimum
material for a given situation.

Two types of viscoelastic material, butyl and EPDM rubbers with various amount
of fillers and plasticisers are investigated. The properties of both rubbers have been
measured over the range of temperatures for frequencies 300-3000 Hz. For this a test
rig had to be modified. For butyl, the best combination of filler and plasticiser gives
temperature weighted noise reductions up to 5.9 dB(A). Butyl rubber is suitable for use
in the rail absorber giving high noise reductions between 0°C and 40°C. The best EPDM
compound gives a temperature-weighted noise reduction up to 6.2 dB(A). Comparing
these two rubbers, EPDM is more suitable for low temperatures below 10°C and butyl is
more suitable for higher temperatures above 10°C.

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Identifiers

ORCID for David Thompson: orcid.org/0000-0002-7964-5906

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