Simulation of tensile behavior of tobacco leaf using the discrete element method (DEM)

The mechanical properties of tobacco leaf are very important for the research and design of tobacco harvesting machines. A numerical model was developed to simulate the tension behavior of tobacco leaf samples using the Discrete Element Method (DEM). The model was constructed with spherical particles bonded together. The model outputs were tensile strength (sigma macro) and Young's modulus (Emacro) of the leaf. Tensile tests were conducted to measure the same tensile properties of tobacco mesophyll samples obtained from different locations of the plant and at different sampling orientations. The model was calibrated and verified by comparing simulation results with the test data. Testing results showed that sampling location and orientation had marginal effects on the tensile properties of tobacco leaf. The average tensile strength was 0.57 MPa and the average Young's modulus was 3.50 MPa. The relationships between model outputs (sigma macro and Emacro) and the two most sensitive model parameters, Young's modulus of particles (Emicro) and the critical tensile stress of bonds (sigma micro) were well described using two equations. The calibrated values of sigma micro and Emicro were 8.02 and 23.07 MPa respectively using the equations and measured values of tensile strength and Young's modulus. The calibrated model was able to predict the tensile strength and Young's modulus of tobacco leaf with relative errors of less than 2 %. The proposed DEM model and method can be applied to other plant leaves in simulating their tensile behaviors and properties.