## 3 Results and Discussion
### Optimization of Bonding Parameters between Epidermis and Inner Flesh of Corn Straw
 \\ \hline
1 & \(5\times 10^{8}\) & \(4.65\times 10^{7}\) & 0.5 & 0.3 & 280.4 \\
2 & \(2\times 10^{8}\) & \(4.65\times 10^{7}\) & 0.6 & 0.3 & 302.4 \\
3 & \(2\times  
The calculation by the constraint solver tool of Design\(-\)Expert shows that when \(X_{9}\) = 2.57 \(\times\) 10\({}^{8}\) N/m, \(X_{10}\) = 3.77 \(\times\) 10\({}^{7}\) N/m, \(X_{11}\) = 0.573 MPa, and \(X_{12}\) = 0.330 MPa, the simulated test damage force is 288 N, and the error is 1.36%, with the actual test average bending damage force of 292 N.  
The values of the bonding parameters are set in the Hertz-Mindlin with bonding module of the EDEM software according to the better parameter values obtained from the above simulation tests, as shown in Table 12. \begin{table}
\begin{tabular}{c c c c c} \hline
**Source** & **Degree of Freedom** & **Mean Square** & **F** & **\(p\)** \\ \hline Model & 14 & 763.56 & 7.08 & 0.0003 \\ \(X_{9}\) & 1 & 17.17 & 0.1592 & 0.6955 \\ \(X_{10}\) & 1 & 99.63 & 0.9240 & 0.3517 \\ \(X_{11}\) & 1 & 2884.23 & 26.75 & 0.0001 ** \\ \(X_{12}\) & 1 & 2256.22 & 20.92 & 0.0004 ** \\ \(X_{9}X_{10}\) & 1 & 20.93 & 0.1941 & 0.6658 \\ \(X_{9}X_{11}\) & 1 & 19.14 & 0.1775 & 0.6795 \\ \(X_{9}X_{12}\) & 1 & 1683.05 & 15.61 & 0.0013 ** \\ \(X_{10}X_{11}\) & 1 & 1654.46 & 15.34 & 0.0014 ** \\ \(X_{10}X_{12}\) & 1 & 377.33 & 3.50 & 0.0810 \\ \(X_{11}X_{12}\) & 1 & 13.14 & 0.1219 & 0.7319 \\ \(X_{9}^{2}\) & 1 & 48.08 & 0.4459 & 0.5144 \\ \(X_{10}^{2}\) & 1 & 406.78 & 3.77 & 0.0711 \\ \(X_{11}^{2}\) & 1 & 703.25 & 6.52 & 0.0220 * \\ \(X_{12}^{2}\) & 1 & 316.88 & 2.94 & 0.1071 \\ Intercept & 15 & 107.83 & & \\ \(\mathrm{Lack\,of\,fit}\) & 10 & 68.45 & 0.3668 & 0.9168 \\ Pure error & 5 & 186.59 & & \\ Cor total & 29 & & & \\ \hline \end{tabular} Note: ** means highly significant (\(p<0.01\)), ** means significant (\(0.01\leq p<0.05\)).  
\end{table} 
Table 11: Analysis of variance of the quadratic regression model for the response surface of the epidermis and flesh bending damage force. Figure 16: Residual diagnostic plot of the whole straw quadratic model. (**a**) Normal plot of residuals; (**b**) residuals vs. predicted; and (**c**) predicted vs. actual. The average value of bending damage force of corn straw is 288 N obtained from five repeated simulation tests under this combination of optimized parameter values, with a relative error of 1.36% from the bending damage force value of 292 N measured by actual physical tests. The bending damage curve of the whole corn straw is shown in Figure 17. The bending damage process of corn straw is divided into three stages, including extrusion deformation, bending damage, and fracture stage, which is similar to the bending damage trend of epidermis and inner flesh. Corn stalks in the actual bending breaking force test the epidermis by the inner flesh support role with the epidermis bending test different will not produce significant cracking, and the whole straw force curve increase rate is greater than the force curves of the skin and inner flesh increased at a rate greater than that of the skin and inner flesh. From the values of the bending damage force of corn straw, the maximum damage force of the whole corn straw is not simply the sum of the maximum damage force of the outer skin and the inner flesh, but is significantly greater than the sum of both. The reason may be that the applied bending force is also transferred between the different structures, and the bonded structure of the outer skin and inner flesh increases the strength of the corn straw when subjected to the breaking force, while acting as a buffer to avoid the phenomenon of collapse of the straw skin and sudden drop of the breaking force. Therefore, the epidermal and inner flesh bonding structures have a significant effect on the bending breaking force of the corn straw and should not be ignored.