## 3 Results and Discussion
### Stress Relaxation Characteristics of Machine-Harvested Seed Cotton
#### 3.2.2 Effect of Trash Content on Stress Relaxation Characteristics  
The trash content increases the bulk density of machine-harvested seed cotton, while the impurities are rich in the higher modulus of elasticity of wood fibers [42; 43]. As shown in Figure 5a, the initial stress of seed cotton gradually increases with the increase of trash content. The main reason for this phenomenon is that the modulus of elasticity of wood fibers such as impurities is large, resulting in the need for a larger compression force for seed cotton at a high trash content [43]. As shown in Figure 5b,c, the \(E_{e}\) increases slightly with the trash content, and the main reason is that the compression force increases with the increase of trash content, and there is a certain transient drop under the larger compression force; while \(T_{1}\) increases with the decrease of trash content, and the minimum value appears at 12%, which is explained by the proper increase of trash content, which can make the seed cotton and impurities easier to bond, but an excessively high or low trash content will hinder the close combination between seed cotton and the impurities [44]. With the increase of trash content, the \(\varepsilon\) shows a fluctuating decrease, and the main reason for this phenomenon is that the trash content of seed cotton is not uniform, and there will be certain pores in the compression process, which makes the \(\varepsilon\) decrease with the increase of trash content.  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Items** & \(E_{1}\) & \(E_{2}\) & \(E_{e}\) & \(p_{1}\) & \(p_{2}\) & \(T_{1}\) & \(T_{2}\) & \(\varepsilon\) \\ \hline Moisture content & \(-0.979\)\({}^{**}\) & \(-0.981\)\({}^{**}\) & \(-0.992\)\({}^{**}\) & \(-0.981\)\({}^{**}\) & \(-0.978\)\({}^{**}\) & \(-0.672\)\({}^{**}\) & \(-0.332\) & \(-0.899\)\({}^{**}\) \\ Trash content & \(0.703\)\({}^{**}\) & \(0.662\)\({}^{**}\) & \(0.949\)\({}^{**}\) & \(0.687\)\({}^{**}\) & \(0.647\)\({}^{**}\) & \(-0.316\) & \(0.035\) & \(-0.175\) \\ Compression density & \(0.913\)\({}^{**}\) & \(0.920\)\({}^{**}\) & \(0.929\)\({}^{**}\) & \(0.918\)\({}^{**}\) & \(0.920\)\({}^{**}\) & \(-0.825\)\({}^{*}\) & \(-0.579\)\({}^{*}\) & \(-0.971\)\({}^{**}\) \\ Cross-sectional dimensions & \(-0.692\)\({}^{*}\) & \(-0.897\)\({}^{**}\) & \(-0.895\)\({}^{**}\) & \(-0.817\)\({}^{**}\) & \(-0.887\)\({}^{**}\) & \(-0.197\)\({}^{*}\) & \(-0.194\) & \(-0.075\) \\ \hline \hline \end{tabular} Note: \({}^{**}\) means extremely significant (\(p\) <0.01). \({}^{*}\) means significant (\(p\) <0.05).  
\end{table}
Table 3: Correlation analysis of stress relaxation characteristics parameters.  
Figure 4: Stress relaxation characteristics at different moisture contents: (**a**) Stress relaxation curve; (**b**) Equilibrium elastic modulus \(E_{e}\) and rapid decay time \(T_{1}\); (**c**) Residual stress ratio \(\varepsilon\).  
Figure 5: Stress relaxation characteristics at different trash contents: (**a**) Stress relaxation curve; (**b**) Equilibrium elastic modulus \(E_{e}\) and rapid decay time \(T_{1}\); (**c**) Residual stress ratio \(\varepsilon\).