# The Influence of Fatigue Loading on the Durability of the Conveyor Belt
## 5 Results and Discussion  
The test was performed with five levels of the mean loading (10 kN, 9.6 kN 8.64 kN, 8.48 kN and 7.68 kN) where its minimum and maximum values ranged within \(\pm\)25% from the mean loading, which achieved the loading ratio of \(R\) = 0.6. In this way, the maximum loading reached values of 95.6%, 91.7%, 82.6%, 81%, and 73.4% in relation to the breaking strength of the belt specimen (13,075 kN). Ten repetitions were performed for all five loading levels. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Characteristic** & **Unit** & **Min** & **Max** & **Value** \\ \hline Breaking strength longitudinally & N/mm & 500 & - & 523 \\ Elongation at break & \% & 12 & - & 29.5 \\ Working elongation—10\% & \% & - & 1.5 & 1.34 \\ Adhesion top cover/1 st ply & N/mm & 3.5 & - & 4.4 \\ Adhesion 1 st ply/2 nd ply & N/mm & 5 & - & 7.6 \\ Adhesion 2 nd ply/3 rd ply & N/mm & 5 & - & 6.8 \\ Adhesion bottom ply/bottom cover & N/mm & 3.5 & - & 4 \\ Tensile strength of cover & N/mm\({}^{2}\) & 20 & - & 20 \\ Elongation of cover & \% & 400 & - & 522 \\ Abrasion resistance & mm\({}^{3}\) & - & 130 & 122 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Characteristics of the selected belt from the manufacturer’s datasheet. Figure 5: Model of a plain-woven EP conveyor belt carcass [40]. Figure 6: Specimens of conveyor belt EP 500/3 Y 526858. Measuring devices, control automation, and adequate preparation of the experiment enabled the conditions for the experiment to be done correctly:  
* There was no slipping of specimens in jaws, and the specimens were placed coaxially with the axis of the device;
* Ball-and-socket joints attached to the tension-loaded cell provided only axial force transfer;
* Ambient temperature and air humidity were monitored so that the experiment would not take place in inadequate conditions;
* The test frequency was 1 Hz in order to avoid additional heat generation in the specimen that could affect results. Figure 7 shows the testing of the specimen in three phases--the initial state, during the test, and the final phase, i.e., the specimen breaking. Table 2 shows the test results. As the results were used at a force ratio \(R\) = 0.6, and since it is the belt tearing force that is important for conveyor belts, and not the tension, a transformation of the fatigue life model given in Equation (2) was made:  
\[F_{MAX}=b\ln(N)+c \tag{5}\]  
where:  
* \(F_{MAX}\) [N]--maximal testing force;
* \(N\)--number of cycles to fracture. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & & \multicolumn{4}{c}{**Loading Level**} \\  & **I** & **II** & **III** & **IV** & **V** \\ \hline Test force mean [kN] & 10 & 9.6 & 8.64 & 8.48 & 7.68 \\ Test force max. [kN] & 12.5 & 12 & 10.8 & 10.6 & 9.6 \\ Percentage of breaking force [\%] & 95.6 & 91.7 & 82.6 & 81 & 73.4 \\ Test force min. [kN] & 7.5 & 7.2 & 6.48 & 6.36 & 5.76 \\ Number of specimens & 10 & 10 & 10 & 10 & 10 \\ Average no. of cycles & & & & & \\ until fracture & 823 & 3168 & 39,180 & 82,472 & 467,568 \\ Standard deviation in number of cycles & 190 & 384 & 2978 & 4619 & 28,521 \\ Relative standard deviation [\%] & 22.9 & 12.1 & 7.6 & 5.6 & 6.1 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Results. Figure 7: Phases of specimen testing: (**a**) initial phase, i.e., undamaged specimen; (**b**) during testing, visible damage; (**c**) the final stage, i.e., specimen breaking. Coefficients \(b\) and \(c\) were calculated from the curve obtained by interpolation based on experimental results. Their value is \(b=-451.2\) and \(c=15\),584. The curve equation, i.e., the curve of the F-N diagram for specimens of the new belt EP 500/3 Y 526858, is  
\[F_{MAX}=-451.2\ln(N)+15,584 \tag{6}\]  
Figure 8 shows the results and the F-N curve graphically. Figure 9 shows some of fractured specimens after fatigue tests. Concerning the fatigue limit, in [42] it is stated that the maximum value of number of cycles for fiber-reinforced composites until fracture that should be considered is 10,000,000.