## 4 Axial Fan Blade Crack Propagation Simulation
### Impact of Combined Centrifugal and Aerodynamic Load  
In the mining operational environment, centrifugal loads combined with aerodynamic loads are applied to axial fan blades, working toward high power and the safety and health of miners from the threats of polluted air and toxic gases during operation. The centrifugal force and the pressure acting on the fan blade grew as a result of the increase in the fan's diameter and the blade's length, resulting in harmful fatigue cracks. In this part, while maintaining the same crack shape and geometry, the FEM of the axial fan blade is established by applying both loads at once. The maximum stress concentration is located on the pressure side of the blade at the right corner of the conjunction of the blade and blade root where the crack is inserted; the same as the case where only an aerodynamic load is applied. Once the static analysis is conducted, a \(N_{step}\) = 18 total number of crack growth steps were performed. Figure 10a, Figure 10b, and Figure 10c present the crack propagation path for centrifugal, aerodynamic, and combined centrifugal and aerodynamic loads, respectively. The crack propagation step's fracture tips of different loads are projected on the plan of the initial crack and are presented as isolines (right figures). The propagation rate of the fracture tips at the two ends (L1 = LA + LB) is significantly higher than the propagation center of the tip (L2), much like the crack propagation under a centrifugal load in Figure 10a, an aerodynamic load in Figure 10b, or a combined load in Figure 10c. Figure 11a illustrates the SIF for mode I along the normalized fracture front for centrifugal load. As can be noticed, the mode I SIF confirms the deviation of the crack propagation path to the left side. This shows that the stress intensity factor is greater on the crack's left side than on the crack's right side. However, for the case of a single aerodynamic load and the case of both centrifugal and aerodynamic loads, the crack tip propagation path moves first in the direction of point A and then rectifies the path to the center. Figure 11b, c illustrates the SIF for mode I along the normalized fracture front for the aerodynamic load and combined load. As can be noticed, the mode I SIF confirms that the crack propagation path is higher on the crack's left side for the first steps and then twisted to the right side to compensate for the deviation. This shows that the stress intensity factor is slightly greater or even equal on the crack's left and right sides. The number of steps (\(N_{step}\)) is divided into three equal steps, \(N_{step}/3\), 2* \(N_{step}/3\), and \(N_{step}\), respectively. For each step, the values of \(L1\) and \(L2\) are presented in Figures 12 and 13. Through the steady increase in both crack propagation lengths \(L1\) and \(L2\), the fracture propagation rate increases. By contrasting Figures 12 and 13, it can be observed that the highest crack growth lengths subjected to the three types of loads occur at the \(N_{step}\), where the values of \(L1\) under a centrifugal load, aerodynamic load, and combined load are 27.05 mm, 38.79 mm, and 37.89 mm, respectively, compared with 8.66 mm, 7.83 mm, and 7.86 mm for the case of L2, which are 3.12, 4.95, and 4.82 times less than \(L1\) with the same configurations. Figure 11: \(Cont\). Figure 10: Crack propagation path under: (**a**) centrifugal load, (**b**) aerodynamic load, (**c**) combined centrifugal and aerodynamic loads. Figure 11: Stress intensity factor KI for: (**a**) centrifugal load, (**b**) aerodynamic load, (**c**) combined centrifugal and aerodynamic loads. Figure 12: The crack propagation lengths of both ends of the crack tip for the three equal subdivisions of the step number. Figure 13: The crack propagation lengths of the center of the crack tip for the three equal subdivisions of the step number. Figure 14. displays the complete crack growth length under various loads.