A New Design Criterion for Wire Rope

Several previous attempts have been made to analyze existing experimental and field data on wire rope running over sheaves, in order to arrive at a basis of design. It is believed that this paper is the first to indicate that a dimensionless bearing-pressure variable B = 2T/UdD is of prime importance in the proper choice of wire rope. Its significance is evident in the plot of life (number of cycles to failure) against this bearing-pressure ratio B, Fig. 1, which shows a well-defined curve for several ordinary lay 6 × 37 ropes. Also, the scatter in test results for many different ordinary lay ropes of 6 × 19 and 6 × 37 construction, Fig. 2, is less than might be expected from the considerable variation in testing procedure and the wire rope itself. In addition, the average curves, Fig. 3, for ordinary lay ropes of different construction all show similar characteristics and fall within the same range. This closeness of agreement in both shape and magnitude can easily be explained on the basis of the compressive stress between the wires but not on the nominal bending and direct tensile stresses that have in the past been considered the important quantities. Plotting against these conventional variables, either singly or in combination, at best leads to families of curves instead of one only for a given construction, thus requiring more data and leading to conclusions which probably have less physical meaning, Figs. 4 (a, b, c, d).