**4. Conclusions**


friction coefficient (*X*5) between the phloem and phloem was constant, the phloem simulation stacking angle increased with the rise in the rolling friction coefficient of the phloem–phloem. When the rolling friction coefficient (*X*6) of the phloem–phloem was constant, the phloem simulation stacking angle increased with the rise in the static friction coefficient (*X*5) between the phloem and phloem. Factor *X*<sup>5</sup> had a more significant effect on the stacking angle than *X*6. Based on the results of the xylem central composite design test, a regression model was established between the rolling friction coefficient (*X*3 ) of the xylem-Q235A steel, the static friction coefficient (*X*5 ) of the xylem–xylem, and the rolling friction coefficient (*X*6 ) of the xylem–xylem and the stacking angle of the xylem. The results indicated that the order of the influence of each factor on the stacking angle is *X*<sup>6</sup> > *X*<sup>5</sup> > *X*<sup>3</sup> .

(4) Utilizing the Optimization module in the Design-Expert software, the optimal parameters for the significant factors of the phloem, xylem, and stacking angle were obtained. Specifically, the static friction coefficient (*X*5) between the phloem and phloem was 0.41, and the rolling friction coefficient (*X*6) between the phloem and phloem was 0.056. The rolling friction coefficient (*X*3 ) between the xylem and Q235A steel was 0.033, the static friction coefficient (*X*5 ) between the xylem and xylem was 0.44, and the rolling friction coefficient (*X*6 ) between the xylem and xylem was 0.016. A twosample heteroscedastic *t*-test was performed on the optimized simulation parameter results and the physical stacking angle measurement results. The results showed no significant difference between the simulated and physical values, with a maximum relative error of 0.79% for the phloem and 0.77% for the xylem, and an average relative error of only 0.4%. This verified the reliability and authenticity of the simulation test, which can provide technical support for subsequent simulation tests on ramie stalk bonding parameters to optimize ramie decorticating machines.

**Author Contributions:** Conceptualization, Y.H. and W.X.; methodology, Y.H. and W.X.; software, Y.H. and Y.D.; validation, Y.H. and L.M.; formal analysis, Y.H. and W.X.; investigation, Y.H. and W.X.; resources, J.L. (Jiangnan Lyu); data curation, J.L. (Jiangnan Lyu) and J.L. (Jiajie Liu); writing—original draft preparation, Y.H. and W.X.; writing—review and editing, W.X. and J.L. (Jiangnan Lyu); visualization, J.L. (Jiangnan Lyu) and B.Y.; supervision, W.X., L.M. and J.L. (Jiajie Liu); project administration, J.L. (Jiangnan Lyu) and W.X.; funding acquisition, J.L. (Jiangnan Lyu) All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the CARS—Bast Fiber Crops (No. CARS-16-E21) and the Natural Science Foundation of Hunan Province (No. 2019JJ40333).

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** All data are presented in this article in the form of figures and tables.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**


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