For practical use, it is of great importance to understand effects of components of rubber compounds on long-term failure behaviors for rubber vulcanizates. The failure behaviors in static fatigue of NBR vulcanizates were studied by the statistical analysis of lifetime distributions. Effects of crosslink density, acrylonitrile (AN) content in NBR, and carbon black fillers (surface area and structure, amount of filler) on the lifetime distributions were examined for the unfilled and carbon-filled systems in the stress relaxation process. The random failure in which a critical crack initiates and propagates unstably occurs in the unfilled systems. It is found that this characteristic failure behavior for the unfilled systems is hardly controlled by the factors such as crosslink density and AN content in the rubber matrix. On the other hand, the wear-out failure in which multi-cracks initiate and propagate stably occurs in the carbon-filled systems. Hence, it is confirmed that the reinforcing filler is the most important factor for noncrystallizable rubbers in the long-term failure process. The fatigue life increases with smaller surface area and higher structure for the filler. However, there apppears to be some suitable amount of the filler for the reinforcement, in particular for highly reinforcing fillers. Thus, it is considered that the effects of the filler on the lifetime distribution in the stress relaxation process are closely connected with the energy dissipation (due to both rubber-filler interactions and microcrack initiations in the rubber matrix) in the vicinity of the filler particules.

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Accelerating abilities of some types of accelerated weathering apparatuses for polyethylene and polypropylene films were examined. Regardless of the polymer materials and the apparatuses, the irradiation time dependence of the elongation-at-break, which was used as a parameter of degradation, was represented by the form y = exp (-Ktⁿ) where y is the retention of the elongation-at-break, t the irradiation time, n a constant arround 2, and K a constant characterizing the accelerating ability. The valid correlation between the apparatus with high energy light and the outdoor exprosure was observed, and this apparatus exhibited very high accelerating ability.

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