Hysteresis and Heating in Vulcanized Rubber

Abstract

Abstract Laboratory tests for evaluating energy losses due to hysteresis are analyzed. The importance of taking into consideration the thermal conductivity and cooling conditions of the rubber sample for the evaluation of heating due to hysteresis losses at temperature equilibrium is discussed. Two new test methods, based on forced resonance oscillations, are described, in which the rubber samples are deformed respectively in shear and in tension at frequencies of 20 to 200 cycles per second, with dynamic shear strain of 0.02 to 0.4 and dynamic tension strain of 1 to 5 per cent, and at a temperature of 20 to 110° C. Experimental results obtained with natural rubber and GR-S gum and tread stocks are presented. The hysteresis losses in gum stocks are found to follow the quadratic law versus dynamic shear strain, and the dynamic modulus G is found to be independent of shear strain. With tread stock the hysteresis losses are lower than would be the case with the quadratic law versus dynamic shear deformation, and the dynamic modulus G decreases with increasing dynamic shear strain. Neither the hysteresis losses nor the modulus depend on the shape or size of the specimen. The modulus is found to be independent of frequency, while the hysteresis losses are found to increase proportionally with frequency. As an application of the test method, results are presented of the effect of the quality and quantity of various types of carbon black on hysteresis heating of GR-S stocks.