An Investigation of the Visco-elastic Properties of Rubber

Abstract

Abstract An account is given of an investigation of the visco-elastic properties of rubber by means of observations on the damping of forced longitudinal vibrations. An attempt is made to determine the visco-elastic limits for rubber, as well as the normal visco-elastic constant τ and the coefficient of normal viscosity E′. The analysis of the experiment predicts the form of the photographic record of the damped vibrations, and gives an expression for τ in terms of the period of vibration and the logarithmic decrement of the amplitude per vibration. Two series of experiments are described in detail. In the first series, where catapult elastic was used, the experimental results are susceptible of detailed analysis. They agree with those predicted by the theory of visco-elasticity when the rate of strain does not exceed 0.1 per second. This is the upper visco-elastic limit. The lower visco-elastic limit for the rate of strain was not reached, so it must be less than 0.017 per second. The value obtained for τ is 28.7×10−4 seconds, and the corresponding value of E′ is 3.42×104 in c.g.s. units. In the second series of experiments pure black rubber was used, and a wider range of frequency of vibration and rate of strain was obtained. Also experiments were carried out at different mean tensions. The experimental results show signs of some unknown disturbance and are difficult to analyze. They suggest 6×10−4 seconds as a probable value Ä , and 0.78×104, for pure black rubber, with a rate of strain 0.1 per second as a probable upper visco-elastic limit (at a mean tension of 150 grams weight). The value of Ä at 300 grams mean tension does not differ significantly from that at 150 grams.