The study analyzes the influence of various factors on the strength and reliable operation of belt conveyors based on rubber composite material. It has been shown that the fatigue strength of composites is a very important factor influencing operation. The degradation process results from the variable load of material between the rollers and the belt tension. This load corresponds to three-point bending with sufficient accuracy. The design of an appropriate attachment that will guarantee such a load during tests on a standard testing machine. Conveyor belts tested in this way can then be safely used in conveyors. In addition, the forces and displacements that will occur during the experiment were considered.