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Dynamic fatigue is thn reduction of the maximum tensile strength of a material by repeated periodic loads or deformations. The dynamic fatigue of vulcanized rubber is basically the result of chemical oxidation processes, destruction during repeated deformations taking place by rupture of the chains throughout the rubber as a result of mechanically activated chemical processes. Physical factors also influence dynamic fatigue. However, the question of the nature and mechanism of dynamic fatigue of vulcanized rubber has not yet been explained ; nor has the relation between fatigue and tensile strength of rubbers been clarified. The results of studies which make it possible to establish the fundamental laws of dynamic fatigue of rubbers and the destruction mechanism during repeated deformations are presented below. Two widely used sinusoidal systems of repeated deformation were studied: (1) constant (maximum) elongations or deformations, ε = const.; (2) constant (maximum) loads or conventional stress, f = const. The number N of cycles before failure and the time before breaking, or the life of a specimen, were determined in these tests. In the first system, the breaking load, fixed by the apparatus, was less than the initial maximum load, owing to the process of “dynamic relaxation“, and in the second system they were equal. The breaking load divided by the initial cross-section and the cross-section at break gives, respectively, the conventional f and the true dynamic tensile strength σ of the specimen.

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