EXPERIMENTAL STUDY OF THE RHEONOMIC PROPERTIES OF BREAKER RUBBER AND RUBBER-CORD COMPOSITE UNDER QUASI-STATIC LOADING

Abstract

Samples of filled breaker rubber and rubber-cord composite were tested for quasi-static cycling loadings with constant strain rates. The dependence of the rubber mix stress-strain diagram on the strain rate was revealed even for low strain rates. A difference was observed between stress-strain diagrams for the first loading and for subsequent ones. The second and subsequent diagrams are close to each other. This effect is referred to in the literature as the Mullins effect. Eight experiments were conducted with different loading programs to determine the manifestation of this effect for breaker rubber. The stress-strain curves depend differently on the strain rate for the first and subsequent loadings. The dependence on strain rate can be described as using the generalized Maxwell model for the first loading, but not for subsequent ones. Moreover, a similar study was done for a bi-ply rubber-cord sample with a 45° cord angle. The same conclusion regarding the Maxwell model applicability was also proven. Finally, numerical simulation of the bi-ply rubber-cord composite was carried out to determine the dimensions of the edge effect zones and, thereby, to estimate the allowable dimensions of the sample. Two types of boundary effects were revealed. Their dimensions were calculated for the 45° rubber-cord sample with various lengths. It was shown that short samples can also be used, if the longitudinal strain is properly recalculated.