The amount of curvature of synchronous belt cords was investigated to understand the fatigue failure mechanism of synchronous belts. At the first step, the curvatures of cords were measured under various mating conditions of belts and pulleys. Then, we analysed the amounts of curvature using a simple mechanical model. The belts used in this study were round-tooth (STPD) with 8mm tooth pitch for high torque drives of automotive engines. The cords were constructed from eleven stranded glass filaments. One stranded glass filament was made of 600 glass fibers. The processing compound of the cords was RFL.
The distributions of curvature were measured along the belt axis. Though the distributions were different between driving and driven sides, the maximum amounts of curvature were almost equal at the both sides. Moreover, the experimental results clearly showed that the maximum amounts of curvature were almost directly proportional to the belt tight side tension, and were inversely proportional to the outside diameter of pulley.
We then proposed a simple mechanical model to explain the experimental results. The effects of tight side tension and distributed loading at the working flank were considered in the model. The analytical results succesfully explained the experimental results.