Biomechanical properties and discrete element modeling of PSR stalks during silage harvest

Existing research on the biomechanical properties of forage crops such as Pennisetum sinese Roxb (PSR) is insufficient to provide essential support for research on mechanized harvesting techniques and equipment. Exploring and studying biomechanical properties of high moisture stalks during silage harvesting can enrich cutting and mechanized harvesting theoretical techniques. The stalks were divided into the inner tissue and the rind and tested based on the degree of lignification. Based on the initial measurements, a discrete element model of the stalk with a diameter of 12.95 mm consisting of 5884 outer particles and 1682 inner tissue particles was constructed. The Bond V2 model was used to simulate the strong forces on tissue fibers and the JKR V2 model was used to simulate the inter-tissue adhesive forces due to high moisture. Cyclic contact separation tests, axial tension tests and radial compression tests based on different internode positions were used for the measurement of stem biomechanical properties and calibration of discrete element model parameters. The maximum separation force between tissues tends to increase linearly with increasing separation velocity, while it can also be roughly considered to increase with increasing intersegmental position. The tensile strength also increases with higher intersegmental position. Physical and simulated cutting tests showed that: cutting resistance decreases linearly with increasing water content; the more perpendicular the tool side plane is to the stalk axis the less damage to the cut section; two sudden changes in cutting resistance caused by crack expansion and tissue fiber breakage divide the cutting process into three stages. The similar physical and simulation test results for contact separation and axial tension as well as the 2.95 % error in cutter resistance in the cutting verification test illustrate the reliability of the discrete element model and parameters. A suitable discrete element model can provide a new research method to further explore and expand the study of biomechanical properties of plant stems and provide a new research method for crop-mechanism interactions in forage mechanized harvesting.