## 4 Conclusions  
With the purpose of improving the abrasive wear resistance performance of soil-engaging components of agricultural machinery, the micro-thorn and convex hull coupled structured surface that was inspired by the cephalothorax exoskeleton of _Procambarus clarkii_ was selected as the bionic prototype. The technical approach of bionic engineering was adopted; bionic single, double and triple micro-thorn coupled convex hull geometrical  
Figure 12: Interaction between abrasive particles and different types of surfaces by EDEM numerical simulation. structured surfaces (Bionic Type 2, 3, and 4, respectively) were designed and proposed. Taking the abrasive wear performance as the evaluation index, the above-mentioned geometrical structured surfaces were compared with the conventional surface without any structures (smooth) and convex hull structured surface without micro-thorn (Bionic Type 1). The rotary abrasive wear testing system was developed and used in this study to evaluate the wear resistance performance of different types of surfaces. The cumulative test time was 80 h, and the total wear distance was 6.09 \(\times\) 10\({}^{5}\) m. Meanwhile, the discrete element method was used to investigate the abrasion mechanism of different types of surfaces. The anti-wear mechanism of bionic non-smooth structured surfaces was investigated. In addition, scanning electron microscopy was used to analyze the wear morphology. After the end of the test, the abrasion loss of the conventional smooth surface sample reached 194.1 mg. The abrasion loss of the Bionic Type 1 surface sample was 154.5 mg, which is 20.4% lower than that of the smooth surface sample. The abrasion loss of the 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 loss of all of the bionic non-smooth surface test samples were less than that of conventional smooth surfaces. Among the bionic non-smooth surfaces, the wear resistance performances of micro-thorn and convex hull coupled structured surfaces were 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, Bionic Type 3 showed the smallest abrasion loss; therefore, it achieved the best wear resistance performance. Scanning electron microscopy (SEM) observation revealed that there were severe wear scars and debris on the smooth surface. The smooth surface suffered much more severe abrasive wear as compared with other surfaces. Among the micro-thorn and convex hull coupled structured surfaces, only minor wear marks and debris were observed. The wear severity for the worn surface of Bionic Type 3 was minimum; hence it showed the best wear resistance performance. The results obtained by the discrete element method EDEM demonstrated that the abraded depth of the conventional smooth surface was the highest, and the average abraded depth of the geometry bin surface reached 1.9766 \(\times\) 10\({}^{-7}\) mm. The average abraded depth of Bionic Type 1 was 1.7221 \(\times\) 10\({}^{-7}\) mm, and the wear resistance performance was better than that of the smooth one, but worse than all of the micro-thorn and convex hull coupled structured surfaces. Among the micro-thorn and convex hull coupled structured surfaces, Bionic Type 3 showed the lowest abraded depth, which was 1.5656 \(\times\) 10\({}^{-7}\) mm. It was further proved that among all the test samples, Bionic Type 3 had the best abrasive wear resistance performance. Therefore, the results obtained from EDEM simulation are consistent with the real scenario experiments. The EDEM simulation further revealed that for the conventional smooth surface, the wear phenomena at different areas were relatively uniform.