Bend- over- sheaves fatigue testing of 2- inch- diameter marine ropes

Many marine ropes are zinc-coated for protection against corrosion. However, the "'in-air'' bend-over-sheaves (BOS) fatigue resistance of zinc-coated rope is thought by some to be inferior to that of bright ropes. Electrolytic zinc coating (Bethanizing) is used to provide heavier coating than available by hot-dipped galvanizing, but the effect of type of coating on the "'in-air"' BOS fatigue resistance of the ropes has not been previously established. The research program reported here was conducted to compare BOS fatigue resistance of 2-inch-diameter galvanized, Bethanized, and bright wire ropes. A method is needed to model the effects of rope construction, steel grade, sheave diameter, and tension on the fatigue strength of wire rope . Models have been proposed in the past, and each was shown to represent the data for which it was developed. Two of these models were used for the data obtained in the experimental work described in this paper together with data from two other programs, but it was found that the models could not account for all the differences among the three programs. An improved model is proposed and examined in this paper.

Author(s): Z. Zimmerman & H.S. Reemsnyder