Stiffness loss of synchronous belts

This paper considers the loss of extensional stiffness of synchronous belts through the life of the belt. It is shown experimentally that the belt extensional stiffness reduces initially with running time, before levelling out to remain constant. The stiffness loss is considered to arise from the development of cracks in the cord which reinforces the belt. The cessation of this loss and the development of constant stiffness is thought to arise from the cracks in the cord running out between the helically wound yarns in the cord, where the crack propagates either into the elastomer compound matrix or along the cord-elastomer compound interface. While this continues to undermine the strength of the belt, it does not serve to reduce the stiffness of the cord or the belt.