Studies of Fatigue Life Evaluation Method and Affecting Factors on Fatigue Lives of Wire Ropes Used in Cranes

Abstract

Accidents involving crane wire ropes remain frequent, partly owing to disposal standards that do not sufficiently account for the fatigue life of wire ropes. This study aims to obtain the basic knowledge for establishing a reliable fatigue life evaluation method and a unified testing procedure to support the appropriate disposal of damaged wire ropes. S- and U-bending fatigue tests were conducted under various conditions. Results showed that the relationship between the logarithm of fatigue life and the mean stress （obtained upon dividing the tension by the nominal cross-sectional area）can be approximated by a straight line. The slope of this line depends solely on the rope type and is hardly affected by the test method. Additional bending fatigue tests using sheaves of varying diameters were conducted to investigate the effect of bending stress on the mean stress–fatigue life relationship. The results reveal that while the slope of the mean stress–fatigue life line remain constant, the fatigue life increases with the sheave-to-rope diameter ratio. U-bending tests, which simulate one-sided bending, show longer than fatigue lives of S-bending tests, although the slopes of the mean stress–fatigue life lines remained nearly identical. Further, fatigue tests were conducted on wire ropes of different diameters to investigate the size effect. The mean stress–fatigue life straight lines are almost identical, indicating that wire ropes within diameters tested in this study remain unaffected by the size. Key words : Crane，Wire rope，Fatigue life，Tension，Size effect