1994-04-01

Minimum Stress Effect on the Fatigue Life of Aircraft Tire Carcass Composites 941177

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. The stress-strain curve of the elastomer composite exhibits strain hardening. As a result, in a stress-controlled fatigue test, shorter strain range or a smaller amount of strain energy is experienced for the same stress range when the level of minimum stress is raised. However, it should be noted mat the test results reported so far are restricted to the case of having minimum stress up to 20% of ultimate tensile strength of the composite. When the minimum stress exceeds a critical level, its effect on the fatigue life of elastomer matrix composite could be quite different.

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