Residual Strength Of Aramid Rope

ABSTRACT Tensile fatigue test and residual strength test were carried out systematically on the strength reduction of braid-on-braid small size aramid rope in our laboratory. Researches on the residual strength of synthetic fiber rope after cyclic loading were rare, although researches on relationship between fatigue life and maximum cyclic load were made. Last year, in 1985, we presented the-study on the residual strength of nylon rope after cyclic loading of constant amplitude. Hence the present research aims at obtaining more sufficient knowledge of the residual strength of aramid rope, and at examining the applicability of Miner's rule to aramid rope. The followings become clear by this systematic and detaited basic test. The strength reduction of aramid rope by cyclic loading in dry condition begins earlier than that reported on synthetic fiber ropes, and proceeds gradually. And Miner?s rule is basically applicable to the failure of aramid rope, and this applicability of Miner's rule indicates the possibility of predicting the residual strength of synthetic fiber ropes, and reducing the time and cost of the failure test or residual strength test. INTRODUCTION Recently the use of synthetic fiber ropes has grown considerably, synthetic fiber ropes are used in the marine environment as mooring hawsers, towing ropes, SPM tethers and so forth. Such ropes can experience many cycles of loading and this cyclic loading may decrease the strength of ropes. Although many break tests and fatigue tests were carried out on synthetic fiber ropes(l),(2),(3), only "a few test concerning residual strength after cyclic loading were carried out(4),(5),(6). The research data on residual strength are insufficient, not withstanding a rope should be removed from service when the residual strength has reduced to the value of retirement criteria. We have presented the data on the residual strength of nylon rope after cyclic loading in 1985(7). In that test, the lower bound of residual strength of nylon rope shows a steady decrease as the number of cycles increases. This result has agreed with J.F.Flory's hypothesis that is similar to Miner's rule on the strength reduction of synthetic fiber ropes (8). Recently in the marine environment, aramid rope has been used or been under evaluation in several systems as tensile strength member. Aramid rope possesses high strength and low elongation in addition to the benefits of lightness and freedom from corrosion that synthetic fiber ropes possess. It is, however, said that aramid fiber reduces its strength rapidly when it rubs against a similar kind of fiber, as a result of its low transverse strength (9). The present research aims at obtaining fundamental knowledge of the residual strength of small size aramid rope, and examining whether Miner?s rule is applicable to predict the cumulative strength reduction of aramid rope