Preliminary study on crop multi-scale mechanics

Crop mechanical properties are widely used in the studies of crop lodging resistance, machine-crop-soil interaction system and crop cultivation. Theoretical support can greatly contribute to the lodging resistance varieties for the quality of machine operation and cultivation. The mechanical properties of crops are also closely related to their morphological structure, anatomical characteristics, and chemical compounds. This review was focused mainly on the mechanical properties associated with the volume fraction of the main compound components (including cellulose, hemicelluloses, lignin, and pectin) in each cell wall layer, the thickness, and the microfibrillar angle. The structure models were also established for the cell wall layer. The elastic mechanics model of each cell wall layer was then constructed using the Halpin-Tsai equation. The elastic model of the cell wall was built using the classical laminate theory and the boundary conditions of each wall layer. The finite element method (FEM) was used to solve those mechanical models. The mechanical properties of the cell and cell wall were characterized by the transmission electron microscope (TEM), scanning electron microscope (SEM), and atomic force microscope (AFM), and confocal raman microscope (CRM). A systematic investigation was made to clarify the influences of cell morphology, structure, size, arrangement, and density on the mechanical properties of tissues. The cell geometry model reconstruction of tissues was performed on the Voronoi diagram, skeleton, ellipse fitting, and high-resolution X-ray microtomography. The mechanical models of tissue were represented by the linear elastic, nonlinear rheological and two-dimensional honeycomb system mechanical model using the finite or discrete element method (FEM or DEM). The mechanical properties of tissue were verified by the micro-scale tension, compression and shear tests. Previous research was found to determine the influence of tissue distribution and arrangement on the mechanical properties of organs. Furthermore, the geometric structure model was also built, according to the characteristics of external morphology and internal microstructure of the organ. The mechanical model of organs was constructed to assign the mechanical property parameters of tissues, and then for the setting load and constraint conditions. FEM was then used to solve the mechanical models. Much effort also focused on the influences of the number, spatial distribution, and arrangement of various organs on the mechanical properties of plants. The plant geometric structure model included the geometric model of each organ, the spatial position, and the posture of each organ on the plant. The mechanical model of the plant was built to assign the mechanical property parameters to each organ in the plant geometric structure model, and then set the connection, constraint mode, and boundary conditions on each organ. The FEM was also used to analyze the mechanical properties of the plant under a specific load. As such, the concept of crop multiscale mechanics was summarized during this time. Namely, the mechanical properties of corps were analyzed to take the cell wall layer, cell wall, cell, tissue, and organ as the basic components, thus building the geometric structure and mechanical models of the cell wall, cell, tissue, organ, and plant, together with the research contents of their structure mechanics. The concept of crop multi-scale mechanics was proposed to systematically summarize the research contents. The findings were also helpful to the formation of crop multi-scale mechanics theory, the establishment of database and the development of analysis software. © 2023 Chinese Society of Agricultural Engineering. All rights reserved.