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

摘要

For application in damping treatments, elastomeric materials should have a highdamping loss factor, but this is inevitably linked to a strong temperature-dependenceof the dynamic properties. A methodology is developed that allows a material to be formulatedfor a particular damping application where temperature-dependence has to betaken into account. The methodology is applied to the case of a tuned absorber systemused for damping the vibration of a railway track. This is required to be effective over atemperature 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 addedsingle-frequency and dual-frequency tuned absorbers. The results show that a high noisereduction can be achieved for the optimum stiffness, provided that the loss factor isbetween about 0.25 and 0.4.In order to study the generic effects of high damping versus constant stiffness, thetime-temperature superposition principle is used to convert frequency-dependence totemperature-dependence for a notional material with constant loss factor. This is used inthe prediction of decay rates and thereby noise reduction. In addition, a weighted noisereduction is studied by using measured rail temperature distributions. This temperatureweightednoise reduction allows a single number measure of performance to be obtainedwhich can be used to assess various elastomeric materials in order to determine the optimummaterial for a given situation.Two types of viscoelastic material, butyl and EPDM rubbers with various amountof fillers and plasticisers are investigated. The properties of both rubbers have beenmeasured over the range of temperatures for frequencies 300-3000 Hz. For this a testrig had to be modified. For butyl, the best combination of filler and plasticiser givestemperature weighted noise reductions up to 5.9 dB(A). Butyl rubber is suitable for usein the rail absorber giving high noise reductions between 0°C and 40°C. The best EPDMcompound gives a temperature-weighted noise reduction up to 6.2 dB(A). Comparingthese two rubbers, EPDM is more suitable for low temperatures below 10°C and butyl ismore suitable for higher temperatures above 10°C.