## 4 Conclusions  
* According to the structural mechanical characteristics of the corn straw, the crushing models of the whole corn straw, the skin of the straw, and the inside of the straw are established, and the grain bonding parameters are checked by combining with the bending destructive test, and the straw bonding parameters are obtained when the water content is 53-65%. The normal contact stiffness of the epidermis is 6.88 \(\times\) 10\({}^{9}\) N/m, the shear stiffness of the epidermis is 4.74 \(\times\) 10\({}^{8}\) N/m, the normal critical force of the epidermis is 379/MPa, the normal critical stress of the epidermis is 320 MPa, the shear critical stress of the epidermis is 30 MPa, the normal stiffness of the inner flesh is 7.2 \(\times\) 10\({}^{8}\) N/m, the shear stiffness of the inner flesh is 3.48 \(\times\) 10\({}^{8}\) N/m, the normal critical stress of the inner flesh is 35 MPa, the shear critical stress of the inner flesh is 0.45 MPa, the normal stiffness of the epidermis-inner flesh is 2.57 \(\times\) 10\({}^{8}\) N/m, the shear stiffness of the epidermal-inner flesh is 3.77 \(\times\) 10\({}^{7}\) N/m, the normal critical stress of the epidermal-inner flesh is 0.573 MPa, and the shear critical stress of the epidermal-inner flesh is 0.33 MPa. * The Hertz-Mindlin with bonding parameters obtained by parameter checking are used to carry out the simulation test of cutting and throwing, and the distance after cutting and throwing of corn straw is measured. Five kinds of throwing distances are obtained at the spindle speed of 600, 625, 650, 675, and 700 r/min. The corresponding throwing distance of each kind of speed is 5410, 5990, 6280, 6950, and 7510 mm, respectively. Figure 18: Comparison of shredded sections of corn straw. (**a**) Actual shredded section of corn straw; (**b**) simulated shredded section of corn straw. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Test Parameters**} & \multicolumn{5}{c}{**Shredder Speed r/min**} \\ \cline{2-7}  & **600** & **625** & **650** & **675** & **700** \\ \hline Throwing & Simulation test & 5410 & 5990 & 6280 & 6950 & 7510 \\ distance /l/(mm) & Bench test & 5760 & 6340 & 6710 & 7420 & 7970 \\ \hline Relative error/\% & 6.1 & 5.5 & 6.4 & 6.3 & 5.8 \\ \hline \hline \end{tabular}
\end{table} 
Table 13: Test comparison and results. * Experimental validation is performed for the simulation results. When the spindle speed is 600, 625, 650, 675, and 700 r/min, the corresponding throwing distances are 5760, 6340, 6710, 7420, and 7970 mm, respectively. The throwing distance of straw fragments increases with the increase in rotating speed, and the influence law is consistent with the actual test. The relative error between the simulation results and the actual test is less than 7%. Thus, it can be shown that the simulation model, as well as the parameters of corn straw, can be used for discrete element simulation experiments of cutting and throwing of corn straw. This paper is limited by the simulation tools in the course of the study, the complex actual operation process is simplified, simulation and experimental studies are carried out on the straw breaking and cutting and throwing process for only five speeds, and there are some differences than the actual operation process. The Hertz-Mindlin with bonding model used in the study is applicable to the simulation of cutting and throwing of corn straw with different tissues and without knots, and further exploration and validation is needed when people use corn straw studies for other characteristics. The effect of nodal straw and blades on the throwing distance is ignored in the validation process.