## 3 Results and Discussion  
### Abrasion Loss and Worn Surface Micromorphology  
Abrasive wear tests were carried out on five types of test samples. As shown in Figure 5, the results showed that there were different severity degrees of abrasive wear on the surface test samples. Among them, the abrasion loss of the conventional smooth surface sample was 194.1 mg. The wear mass of Bionic Type 1 surface sample was 154.5 mg, which was 20.4% lower than that of the smooth surface sample. The abrasion losses of Bionic Type 2, Bionic Type 3 and Bionic Type 4 test samples were 20.9, 11.5 and 63.1 mg, which were 89.2%, 94.1% and 67.5% lower than those of the conventional smooth surface sample, respectively. It was demonstrated that the abrasion losses of all of the bionic non-smooth surface test samples were less than that of conventional smooth surface ones. Among the bionic non-smooth surfaces, the wear resistance performances of micro-thorn and convex hull coupled structured surfaces were substantially further improved as compared to that of the convex hull structured surface without coupled micro-thorn. Among the micro-thorn and convex hull coupled structured surfaces, the Bionic Type 3 had the smallest abrasion loss; therefore, it achieved the best wear resistance performance. To mitigate the problem of the wear failure of soil-engaging components of agricultural machinery, many researchers also applied the bionic approach to the structural surface design to improve component wear resistance. For example, [PERSON] et al. [50], inspired by the ridged structures on Pangolin _squama_ and _Chlamys farreri_ shell surfaces, demonstrated that that the mass loss of bionic samples was less than that of the flat surface samples. The wear resistance improved, ranging between 33.1% and 77%. [PERSON] et al. [2] learned from the _Copris ochus_ Motschulsky, and designed bio-inspired embossed surfaces consisting of an array of convex domes, and proved the abraded volume reductions ranged between 12.1% and 58.1%. [PERSON] et al. [24] established an abrasive wear system composed of pangolin scale and abrasive sand based on the discrete element method (DEM), and proved that the geometrical shape of the pangolin scale is helpful for decreasing the boundary stress, especially with the wear rate decreasing when the velocity is higher than a certain degree. As shown in Figure 6, after 80 h of accumulative test time and the total wear distance of 6.09 \(\times\) 105 m, the micro-thorns were well preserved. The edges of the micro-thorns were generally neat, even though some fraying was present. Figure 5: Abrasion loss of 5 types of test sample. Figure 6: Wear surfaces in macroscopic scale of five types of abrasive wear experimental samples (the direction of abrasive material is from left to right). Figure 7 shows that the variation pattern of abrasion loss of five different types of test samples behaved differently. Among all the test samples, the wear rates of the conventional smooth surface and Bionic Type 1 fluctuated greatly with time. Generally, in the first 20 h of wear time, the differences in wear rates of all the test samples were not obvious. However, after 20 h of wear time, the wear rates of the conventional smooth surface and Bionic Type 1 were dramatically increased. Over 80 h of wear time, the wear rates for all of the three micro-thorn and convex hull coupled structured surfaces (Bionic Type1, Bionic Type 2 and Bionic Type 3) were stable and much less than the conventional smooth surface and convex hull structured surface. Among three of the aforementioned test samples, after 50 h of wear time, the wear rates of Bionic Type 2 and Bionic Type 3 slightly decreased with time; however, Bionic Type 4 showed an obviously upward trend. The worn micro-morphologies of the sample surfaces are shown in Figure 8; it was observed that there were different sized micro grooves and flakes on the surface of test samples, indicating that micro cutting and plastic extrusion peeling occurred during the abrasive wear process.