(1) slip on the pulley, can not transmit power.
(2) due to fatigue caused by delamination, tear and pull off.
(3) with the face of wear.
(4) torsional vibration of the driven shaft.
To ensure that the belt does not slip at work, and has a certain degree of fatigue strength and service life is the main basis for V-belt design, but also by friction drive the other belt drive the main basis for the design.