Study of Fracture Behavior of Cord-Rubber Composites for Lab Prediction of Structural Durability of Aircraft Tires II. Fatigue Damage Accumulation of Bias Carcass 922011

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. The involvement of material degradation process was indicated by the fact that gross failure of composites requires lower value of dynamic creep when the frequency is increased. At the same time, the use of higher frequency resulted in exponentially higher dynamic creep rate. For load range tested, the energy loss per cycle was found to be nearly constant and independent of the frequency. As a result, the energy loss per unit time became linearly proportional to the frequency. Since fatigue life of carcass composites is linearly proportional to the inverse of frequency, it was postulated that the rate of energy loss determines the lifetime of composites. The study revealed that the specimen surface temperature may not describe such critical parameters as internal heating particularly at the point of crack initiation or true heat dissipation rate.