## 3 Simulation and Analysis  
### Qualitative Analysis  
Using the dynamic abrasive wear system, the abrasive wear behavior of the arranged pangolin scales subjected to abrasive sand were simulated with velocities of 0.50 m\(\cdot\)s\({}^{-1}\), 0.62 m\(\cdot\)s\({}^{-1}\) and 0.74 m\(\cdot\)s\({}^{-1}\), respectively. Figure 5 shows the morphology of the scales after wearing at 0.05 m and 0.10 m under each velocity. The figure shows that the wear degree of the scales increases continuously with the increase in the number of contacted sand abrasives. After a process of rapid growth, the wear rate and wear extent decrease and reach a stable state. Only the tip part of the scale is worn off by the abrasive sand when the velocity is 0.50 m\(\cdot\)s\({}^{-1}\). The wear extent increases with the wear velocity, until severe fracture and slip appear at a velocity of 0.62 m\(\cdot\)s\({}^{-1}\). When the velocity is over this value, the wear extent slows down. It is obvious that the tip of the pangolin scale is worn severely, and the wear part is separated from the pangolin scale. The worn part finally reaches an arc. Figure 6 shows the dynamic contact bond fields of the pangolin scale under different velocities. The contact bond is the inherent structural strength of the biological surface, which reflects the fracture mechanism; the structural strength will be broken once the acting forces of abrasive sand on the pangolin scale exceed the contact bond strength [13], thereby causing the breakaway of the wearing parts from the pangolin scale, as well as partial fracture and injury. The figure shows that the contact bond of the tip is severely broken. One reason for this is that the total structural force in the tip is less than other parts. Furthermore, greater cohesion in the lower layer of the sand contributes to the fracture of the tip. The contact bond can also be seen when the wearing parts are separated from the pangolin scale. According to the contact bond fields, microscopic injury and deformation were observed. Therefore, the fracture trend at the following moment can be predicted through the contact bond fields. Figure 4: Abrasive wear tester based on rotary abrasive disc. (**a**) Photograph of the tester, (**b**) schematic diagram of the tester. Values 1–3 indicate the compacting wheels; 4 is the scraping plate; 5–8 refer to the test specimens; 9 indicates the subsoiler; 10 is the abrasive rotary disc. Figure 5: _Cont._Figure 5: The abrasive wear morphology of pangolin scale. Figure 6: The dynamic contact bond field of the pangolin scale and abrasive sand. Figure 7 shows the dynamic contact force chains between the pangolin scale model and the abrasive sand. The contact force contains contact stress and contact tension, which reflects the dynamic force in the simulation system. In Figure 7, the size of the line represents the value of the contact force. The nonuniformly distributed force in the scale is observed from the contact force fields. The size and the direction of the contact forces are the main reasons for the fracture of the pangolin scale. The wear simulation by DEM shows the desquamating behaviors of the wear parts subjected to the abrasive sand. As long as the normal stress is larger than the normal contact bond strength (shown in Table 1) or the tangential stress is larger than the shear contact bond strength (shown in Table 1), wear will appear. The cracks and the injuries were generated by the discrete forces on the scale, and the failure extent intensified when the forces increased. From the dynamic contact force fields, due to the stress concentration, it can be seen that the corners of the pangolin scale suffer severely from stress concentration, where the fracture extent is greater. The fractures occurred because of tensile stress. This indicates that the partial stress on the scale structure is largest under a velocity of 0.62 m/s. When the wear extent becomes stable, the acting forces at the corners of the pangolin scale tend be distributed uniformly.