Tire tread, transferring the car forces on the road, is fundamentally based on highly filled, cross-linked and topologically entangled rubber blends, which show an excellent damping behavior. Thus the tire tread commonly is exposed to high dynamic loading conditions, fur-thermore the tire tread is naturally influenced with physical processes caused due high tem-perature fluctuation, ozone concentration, solar radiation, influence of fluid medium, etc. These extreme requirements have a significant effect on the fatigue and failure tire tread behaviors, whereas these processes particularly lead to the degradation of the mechanical behavior of rubber matrix. The initiation of local instability in tire tread due to failure is par-ticularly caused by micro-crack initiation. Its propagation could have fatal consequences be-cause of the resulting global tire’s instability and thus high potential danger caused due to car accident. Hence the understanding of the crack initiations and its propagation in rubber regarding to the applied physical processes as well as loading conditions is a subject of high scientific interest. Its description will improve the safety, higher durability and life service of the tire as well.
It is well known, that the mechanical and specially fracture behaviors depend on the struc-ture of rubber matrix. Particularly the characteristic behavior are based on the filler network build with the nanoparticles, size of filler cluster, interaction of filler-filler- and polymer-filler-bonds and the specific surface of filler under the identical compounding conditions [1, 2]. The effect of rubber reinforcement caused due to rubber modification with various fillers on crack or fatigue resistance has been studied in a lot of publications [1, 3, 4] and are well described.
The naturally applied physical processes, which the tire tread is exposed, cause the aging of rubber matrix. The main importance has oxidative attack with simultaneously actuating thermal processes. The oxidative degradation of a sulphur cured rubber proceeds via at least one chain reaction sequence which introduces C-C and C-O-O-C crosslinks between polymer chains and another sets of chain reactions between oxygen and the sulphur atoms. If the thermal processes take an influence, it is necessary to balance the rate of reaction of oxygen with the elastomer and the rate of diffusion of the oxygen into the bulk material. If the tem-perature is relatively low, it has been evaluated that for cured rubber diffusion predomi-nates and therefore there is slow oxidation throughout the product. Contrariwise as the thermal activity rises, the rate of oxidation increases significantly than the rate of diffusion. Thus a substantial oxidation occurs on the surface at higher temperature and a brittle oxi-dized surface is formed. The critical stress of polymer chains in an oxidized rubber surface occurs in a lower strain compared to the not oxidized material, thus the mechanical proper-ties of rubber degrade.
Generally the aging is interconnected to loss of mechanical properties over the whole life-time of the tire tread . The most efforts in this field of research were only investigated to the observation of crack propagation respectively rupture of rubber test specimens under quasi-static loading conditions with no relationship to the fatigue behavior of rubber matrix. Huang et al.  studied the phenomenon of cyclic ageing on Natural Rubber (NR). They found, that for NR, aging at lower temperatures leads to a decrease in modulus, while at higher temperatures it leads to an increase in modulus. Bauer et al.  studied the mechani-cal properties of skim tire based on Butadien Rubber (BR) under the oxidative aging with fill gases 50/50 blend of N2/O2 at various temperatures in the range from 50 to 70°C. They demonstrated the decreasing of elongation-to-break and increasing of modulus versus time of aging in the whole range of temperatures. This decreasing in mechanical behavior leads to high inclination of rubber material to the failure and proves the initiation of micro-cracks.
The micro-cracks in tire tread caused due to natural physical aging are initiated at tire steady state because while rolling the stress states in tire under dynamic loading condition have a predominant influence on micro-crack initiation.
The aim of this study is to determine the influence of thermal aging processes at common atmosphere in dependence on exposing time as well as the varied temperature directly in-fluencing the loaded rubber test specimen on fatigue crack growth (FCG) behavior under dynamic loading condition. In the present study, FCG behavior of Natural Rubber (NR) and Styrene-Butadiene Rubber (SBR) blends suitable for tire tread application has been investi-gated.