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The question of how the static strength of angle-plied nylon cord-reinforced rubber composites simulating aircraft tire carcass is affected by damage accumulation or materials degradation was examined in this study. Upon cyclic loading at 1 Hz, residual tensile strength was gradually lowered with the progression of fatigue damage. The degradation of the residual strength became more drastic toward the end of the fatigue life because of worsening delamination. In contrast, the residual strength after cyclic loading of 10 Hz exhibited a rapid decrease at the beginning of the fatigue life, presumably due to thermal degradation, and then remained virtually constant throughout the life. Acoustic emission (AE) activities were monitored to assess the extent of damage and to explore a possibility of indirect monitoring of residual strength of composites.

The effect of minimum stress on the fatigue life has been assessed for an angle-plied nylon cord-reinforced elastomer composite which represents the bias aircraft tire carcass. The S-N curves were established under constant minimum stress rather than constant R-ratio. In this manner, all data points in each S-N curve could be associated with the same level of creep stress. Composite laminate specimens exhibited a normal failure sequence of fiber-matrix debonding developing into the delamination under cyclic tension. A trend of longer fatigue life of the composite was clearly observed at a given stress amplitude with a higher level of minimum stress. The use of a higher level of minimum stress also caused the increase of the fatigue endurance limit of the composite. The trend of longer fatigue life with a higher level of minimum stress stems from the fact that the stress and strain are not linearly related to each other.

Current phase of the study was undertaken to examine tensile fatigue behavior of cord-rubber composites representing bias tire carcass under various frequencies up to the level which closely simulates loading during high-speed take-off of aircraft. At a given stress amplitude, the use of higher cyclic frequency was found to affect strain response and heat build-up characteristics of composites significantly. The lower level of initial strain observed at higher frequency stems clearly from strain rate dependence of deformation of rubber matrix composites. The temperature profile of the specimens subjected from 20 to 30 Hz loading showed that hysteretic heating under these conditions may lead to thermal fatigue failure as well as chemical degradation influencing both fiber-matrix adhesion strength and matrix strength.