Accidental Factors Involved in the Fatigue Breakdown of Rubber Articles

Abstract

Abstract Poor dispersion of compounding ingredients, and the presence of granules and of impurities which in some way get into vulcanized rubber and thereby disturb the normal distribution of stresses in an article and thus cause local stress concentration, are regarded as accidental factors in the fatigue breakdown of vulcanized rubber. This problem was studied by developing, by means of the photoelastic method, an adaptable schematic representation of the phenomena. Although only a qualitative evaluation of the local disturbance of the system of stresses caused by these factors is possible, in the particular case of granules, it has been found that the closer a granule is to the outside surface of the rubber article, the greater is the disturbance of the system of forces. Furthermore, the local stress concentration is greatest when there is no adhesion between the granules and the surrounding vulcanized rubber. Finally the stress concentration caused by a small cut or incision made at various locations on a rubber test-strip under tension is considered. This case has been included because fatigue cracks first become manifest in this form.