1995-05-01

Acoustic Emission and Residual Strength of Aircraft Tire Carcass Composites 951418

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. Total cumulative values of AE hits, counts, and energy, which were defined at the final point of gross failure in static tension, were proportional to the residual strength independently of the frequency used in previous fatigue loading. The observation indicates that, subjected to static tensile loading, initially stronger or less fatigue-damaged composite specimens can sustain more damage and therefore produce greater amounts of AE activities up to failure. For indirect monitoring of residual strength, the accumulation rates of AE activities prior to the delamination were also measured for virgin specimens as well as the specimens previously subjected to fatigue loading. The accumulation rates of AE activities under static tension were found to be proportional to the residual strength.

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