Fatigue data for nylon and polyester marine ropes from several testing programs in Europe and the U.S. are compared and analyzed. Failures at loads above 30-40% of the new breaking strength for nylon or 60-70% for polyester can be predicted by a model based on the creep-rupture behavior of individual fibers and yams. Failures at lower loads and higher cycles usually occur by external or internal abrasion, following a steeper S-N curve trend; an abrasion model is presented that correlates well with these data. Polyester outperforms nylon under wet conditions in both regimes of be havior for a wide range ofrope samples. Additional topics discussed are thermal failures from hysteretic heating in dry ropes, and changes during cycling in rope load-extension, hysteresis, and residual properties.
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