2.4.2. Establishment of the Discrete Element Model for Ramie Stalk Analysis of the Ramie Stalk Model

An analysis of the ramie stalk structure's composition was conducted to establish a discrete element model for the ramie stalk. The cross-section of the ramie stalk was approximately circular, with the outer to inner cross-sections consisting of the green husk layer, phloem, xylem, and central medulla, as shown in Figure 5. The central medulla is foam-like, with a loose tissue structure and irregular shape. At the same time, the green husk layer was very thin and brittle, both of which have negligible mechanical properties compared to other components.

**Figure 5.** Schematic diagram of the structural composition of the ramie stalks.

Mechanical decortication of ramie stalks is performed by rolling and crushing the xylem with a roller to separate the xylem from the phloem, indicating that the breaking strength of the xylem was less than that of the phloem. From this apparent perspective, it can be assumed that the material properties of the green husk layer and the central medulla can be ignored, and the ramie stalk can be regarded as a combination of phloem and xylem materials. Therefore, only the phloem and xylem should be considered when a discrete element model for the ramie stalk is established. The geometric model is shown in Figure 6. In this paper, the phloem was a composite of the green husk layer and the phloem fibers, and the physical tests did not remove the green husk layer.

**Figure 6.** Ramie stalk geometry model: (**a**) ramie stalk structure simulation; (**b**) idealized cross-section of the ramie stalk.
