Mechanics of Bend-Over-Sheave (Shoeshine) Fatigue Testing of Cord-Rubber Laminates

Abstract The Bend-Over-Sheave test is used for screening reinforcement cords used in tires, especially on fatigue interply delamination as well as rubber-fabric and rubber-cord adhesion degradation. The typical cyclic load of tension-tension of the sidewalls or tension-compression of the belt can be achieved by the proper definition of two-ply laminates bent over a sheave. The objective of this paper is to define relevant fatigue test conditions that can predict the performance of new materials. A finite element model of the Bend-Over-Sheave test configuration is presented and shows that, for the test arrangements studied in this paper, flanged wheels should be used to prevent lateral buckling in the compressed cords. Besides, a simplified model enables us to determine the different factors that have significant effect on the strain levels in the cords. The material of the cords, the rubber hardness (“Shore”), and the sample manufacturing process are shown to have an influence on the specimen strain levels. The test conditions, i.e., the sheave radius, the traction force, and the contact angle between the sheave and the sample, also affect the behavior specimen strain levels. On the other hand, if the sample length is higher than a certain value, it is shown not to have a significant effect on the results.