Fatigue is the common cause of most V-Belt problems. Wear is usually a result from the belt loosing tension and “rolling” around the pulleys. High belt anxiety, immoderate slippage, unfavorable environmental conditions, and overloads caused by shock, vibration, all make contributions to fatigue.
The transmission in belt force is a result of friction between the belt and pulleys. But, some relative movement will continually exist at driving force-belt interface and belt-driven pulley interface because of ineffective friction. This phenomenon is called as slip the V-Belt. Because of slip, its speed will be much less than the peripheral speed of the using wheel and slightly more than the peripheral velocity of the driven wheel.

V-Belt