A Study On Mechanical Properties And Dynamic Laws In Wheat Growth

A study on the mechanical properties and dynamic laws of wheat in growth belongs to a biomechanics. In this paper, using the basic principles of mechanics and methods of engineering design, the mechanical properties of root, stem and leaf of wheat and the stress-strain relationship of soil-root composite and the dynamic laws under wind were researched by the method of combining analysis and experiment. The main contents are:1. The mechanical properties of major organs of wheat were systematically studied in this paper. The stress-strain curves of the root, stem and leaf of wheat were obtained under the conditions of the basic deformation including the tension, bending, compression and shear. The main indicators of the mechanical properties of root, stem and leaf of wheat were measured. The laws of deformation and failure of root, stem and leaf of wheat are analyzed under force. The results show that root, stem and leaf of wheat have different strength and stiffness. The strength of stemσ_j≈21.85-74.91MPa; the modulus of elasticity E_j≈0.58-5.14GPa, average 1.5GPa; the strength of the leafσ_y≈2.04-9.54MPa, the modulus of elasticity E_y≈83.90-303.40MPa; the strength of primary rootσ_g≈11.4-57.25MPa, the modulus of elasticity E_g≈l37.6-470.5MPa; the strength of secondary rootσ_g≈1.07-13.07MPa, the modulus of elasticity E_g≈114.3-470.4MPa. The longitudinal and transverse properties of the compression and the shear for wheat stems are obviously different; the longitudinal compressive strength of stemσ_jz≈7.40MP>the transverse compressive strength of stemσ_jh≈0.62MPa; the transverse sheering strength of stemÏ„_jh≈6.21MPa>the longitudinal sheering strength of stemÏ„_jh≈0.34MPa. The longitudinal tensile strength of leaf is higher then the transverse tensile strength; the longitudinal tensile strength of leafσ_yz≈4.85MPa>the transverse tensile strengthσ_yh≈0.44MPa. The deformation of stem is mainly the cantilever bending during the growth of wheat. The failure of wheat stem is firstly occurred in bending side at the foot of a stem. The stem will rupture along the fibers of stem when the stem being compressed. When the root, stem and leaf of wheat being tensioned longitudinally, the fracture is occurred in cross-section of them. The strength and stiffness of root, stem and leaf is the interior cause that enables wheat to grow under the complex exterior conditions and is the basis of developing and using root, stem and leaf of wheat.2. From the perspective of engineering materials research, the microstructure of root, stem and leaf of wheat were observed and analyzed in using electron microscope technology. The results show that root, stem and leaf of wheat are a typical material of porous, discontinuous, non-homogeneous and anisotropic. The mechanical properties depend on its organizational structure and chemical composition. The cross-section of root, stem and leaf of wheat look as if a cellular, the crisscross between dense organizations and porous organizations; longitudinal section looks as if composite materials made of multi-fiber and matrix. Mechanical organizations of outer-epidermis of root, stem and leaf are thick and high-density. The fibers (organizations of thick-walled cells of vascular) are the major component to bear. The role of matrix (organizations of thin-walled cells) is to link and transmit. Distribution of stem fiber density increases along the radial from the wall to the outside gradually, resulting in the best structure of a stem bending.3. The mechanical model of soil-root composite system is established in this paper; the relationship of stress-strain and the calculation method of engineering constant of soil-root composite were discussed; the relationship between soil stress and wheat roots growth was analyzed. The results show that a normal stress is related to the normal strain, the engineering constants and Poisson ratio; its shearing stress is direct proportion to the shearing strain and shearing modulus of elasticity. The strength of the soil-root composite depends on the friction between roots and soil particles and coherent force between soil particles and roots, and soil particles; the root s contributions to strength of the composite come mainly from the friction between roots and the soil particles; coherent force C=25.21-43.60KPa, friction angleΦ=23.73-35.33°. The friction and coherent force not only relate to the properties of the rootand soil, but also the amount of root and moisture content. The calculation formula of the strength of root-soil composite isÏ„=(25.1-43.6)+σtan(23.73⁰-35.33⁰). Research shows that distribution of crop roots in soil is exponentially curves. The number of crop roots, root length, and roots surface area decrease with the increase of soil stress.4. The mechanical model in wheat growth was established under wind. The motion differential equation of wheat growth maturity was obtained under the conditions of wind. The dynamic response of random vibration in wheat growth was analyzed under the conditions of instantaneous and continued wind. The results show that the dynamic response and the strength of vibration for wheat stem system is related to the morphology of stem system(ear of wheat, number of leaf and angle, windward area, height, mass, geometry, cross-section area, moment of inertia), the properties of the stem materials(elastic modulus, shear modulus, damping),natural environmental conditions(wind speed and pressure, pulse of wind, distribution of wind speed, ground roughness, location), and soil conditions (humidity and the degree of soil soft).The bending vibration differential equation in wheat growth under the conditions of wind:The dynamic formula in wheat growth under the conditions of wind:...