Dynamic Properties of Various Rubbers at High Frequencies

Abstract

The shear wave velocity and attenuation of GR‐S, Butyl, Hevea, Hycar, and Paracril rubbers have been measured in the frequency range 0.2–7 Mc/sec and the temperature range −60°C to 20°C. To minimize errors arising from interfaces in the acoustic path, a double path technique was used. By combining the shear wave data with bulk wave data the dynamic shear, bulk, and Young's moduli, and their associated viscosities, were calculated. The results were coupled with low‐frequency Young's modulus data on the same materials to give information over many decades of logarithmic frequency, and from this the distribution of relaxation times was determined. To a fair approximation, in the range investigated, it was found that the real and imaginary parts of the dynamic Young's modulus could be taken as equal to three times the corresponding values of the dynamic shear modulus. It was found that the classical Stokes assumption, that the bulk viscosity is negligible in comparison to the shear viscosity, was reasonable for some of the rubbers, but not for all of them.