A New Method for Determining the Dynamic Mechanical Properties of Rubber

Abstract

In submarines, machinery with reciprocating rotating parts is placed on rubber mountings to isolate noise and vibration from the hull of the vessel. Otherwise the hull would radiate the noise to the sea and facilitate detection of the submarine by the enemy. The dynamic mechanical properties of the rubber in the mountings determine to a large extent their effectiveness in isolating noise and vibration. Only within the last ten years has reliable information become available on the dynamic mechanical properties of rubber at high frequencies of vibration. Most of this advance has been due to Nolle. Other workers in this field have been Witte, Mrowca and Guth, Hillier, Cramer and Silver, and Morris, James and Snyder. Nolle gave an excellent description and analysis of techniques for measuring the dynamic mechanical properties of rubber in the frequency range of 0.1 to 120,000 cycles per second (cps). The methods which he described were identified as rocking-beam oscillator, vibrating reed, strip transmission, strip resonance, and magnetostriction. Guth and associates, Hillier, and Cramer and Silver used the strip transmission method in their respective investigations. Morris, James, and Snyder used a bar transmission method which had not been previously described. This paper deals with a modification of the bar transmission method, whereby the resonant frequency and dispersion of the vibrational energy above and below the resonant frequency are measured. From this information the velocity of sound, Young's modulus, and loss factor of the rubber are calculated.

Phase Velocity of Rubber Element in Vibration Isolator Under Static Load

“…The experimental results obtained [28] are given in Table 2, which at di!erent values of the compression ratio and wavelength ! , lists the measured values of the longitudinal resonant frequency f + .…”

“…of the longitudinal wave in the e!ective rubber cylinder. Morris et al [28] investigated the dynamic properties of rubber using a modi"ed bar transmission method developed from the strip transmission, or longitudinal wave resonance method described by Nolle [39]. They measured the longitudinal wave velocity of a cylindrical rubber specimen under static compression, by determining its longitudinal resonant frequency.…”

“…Equation (22) is also approximately true for rubbers that have low loss factors, such as un"lled rubbers, since the loss normal modulus is small compared to the elastic normal modulus. The cited experimental work has been conducted at frequencies up to approximately 400 Hz [28] and room temperatures of approximately 18}233C.…”

“…The precision of reproducibility of the resonant frequency f + is given as 8 in 330 Hz [28], i.e., 2)4%. As can be seen from Table 2, the predicted resonant frequency f !…”

“…. For the test set-up used, the wavelength was equal to twice the length of the compressed rubber specimen [28], which gave ! .…”