【作者】 郭维俊；

【导师】 黄高宝；

【作者基本信息】 甘肃农业大学 ， 作物栽培学与耕作学， 2008， 博士

【摘要】 小麦生长过程中根茎叶力学特性及其动力学规律的研究属生物力学范畴。本文运用力学的基本原理，借鉴工程设计思想，采用试验研究与理论分析相结合的方法，主要研究了小麦生长成熟期根、茎、叶的力学性能、根系-土壤复合体的应力-应变关系和风力作用下小麦茎秆的动力学规律。1．围绕力学性能，全面系统地研究了小麦成熟期根茎叶的力学特性，测得了根茎叶在拉伸、弯曲、压缩和剪切四种基本变形条件下的应力-应变曲线，获得了表征根茎叶强度、刚度和稳定性的主要评价指标，分析了根茎叶在外力作用下的变形规律和破坏规律。结果表明：小麦根茎叶具有不同的强度和刚度。茎秆的强度σ_j≈21．85～74．91MPa，弹性模量E_j≈580～3140MPa；叶片的强度σ_y≈2．04～9．54MPa,弹性模量E_y≈83．90～303．40MPa；初生根强度σ_g≈11．4～57．25MPa，弹性模量E_g≈137．6～470．5MPa；次生根强度σ_g≈1．07～13．07MPa，弹性模量E_g≈114．3～470．4MPa。茎秆的纵向、横向的抗压性能和抗剪性能有明显差别，纵压强度σ_jz≈7．40MP>横压强度σ_jh≈0．62MPa；横剪强度τ_jh≈6．21MPa>纵剪强度τ_jh=0．34MPa。叶片的纵向拉伸强度高于横向撕裂强度，叶片纵拉σ_yz≈4．85MPa>横撕σ_yh≈0．44MPa。小麦生长状态下茎秆的变形主要是悬臂弯曲，其破坏一般首先发生在根部附近的弯曲一侧，大多在第二节间；茎秆轴向压缩时，茎秆沿纵向纤维方向破裂；根茎叶轴向拉伸时，均在横截面发生断裂。根茎叶具有的强度和刚度，是小麦在复杂外力作用下能正常生长的主要原因，是根茎叶资源工业开发利用的基本依据。2．围绕组织结构，观察了小麦根茎叶微观组织的解剖构造影像，分析了根茎叶机械组织、薄壁组织和输导组织与力学性能之间的关系，比较了根茎叶微观组织结构的差异及其对力学性能的影响程度。结果表明：小麦根茎叶是多孔、不连续、非均匀、各向异性材料；根茎叶的横截面形如蜂窝，密实组织和多孔组织交错；纵向截面如同多层纤维组成的复合材料。根茎叶的承载能力主要决定于它们的机械组织（厚壁细胞组织）的层数（厚度）和纤维组织的排列形式；根茎叶外表皮机械组织发达、密实度高；维管束厚壁细胞（纤维）是主要的承力元件，薄壁细胞（基体）则起连接、传载作用。茎秆纤维密度沿秆壁径向由里向外逐渐增加，因此形成了茎秆承受外载弯曲的最佳结构。3．根据复合材料，建立了小麦根系-土壤复合体的力学模型，得到了根系-土壤复合体的应力-应变公式，探讨了根系-土壤复合体工程常数的计算方法，分析了小麦根系发育生长与土壤环境、土壤应力之间的相互关系。结果表明：土壤-根系复合体任一方向的正应力，不仅与各方向的应变分量有关，而且还与各方向的工程常数密切相关，与泊松比的关系更为复杂，其剪应力与相应平面的剪应变和剪切弹性模量成正比。土壤-根系复合体的强度，取决于土粒与土粒、土粒与根系之间的内摩擦力和黏聚力；粘聚力和摩擦力不仅与土壤、根系的材料特性、组织结构有关，而且与含根量、水分含量相关。粘聚力C≈25．1～43．6KPa，摩擦角Φ=23．73⁰～35．33⁰,根系-土壤复合体的强度τ=（25．1～43．6）+σtan（23．73⁰～35．33⁰）；根系对复合体强度的贡献，主要来源于根与土粒之间的摩擦力。研究表明：作物根系在空间的分布随土壤应力的增大呈指数曲线变化；土壤应力增大，作物根量、根长、根系表面积递减。4．围绕动力性能，建立了小麦生长成熟期风力作用下的力学模型，推得了小麦成熟期风力作用下的微分方程，系统研究了小麦成熟期在瞬时风力和持续风力作用下的动力响应，得到了小麦成熟期风力作用下的频率方程、主振型函数、运动方程和强度评价公式。结果表明：小麦在随机风力作用下茎秆系统的响应和振动强度，与茎秆系统形态、茎秆系统材料性质、自然环境条件、土壤状态等因素有关。具体参数涉及叶片数量及其夹角、迎风面积，茎秆高度、茎秆形态、横截面积；麦穗质量、叶片质量、茎秆质量、茎秆转动惯量、茎秆弹性模量、茎秆剪切模量、茎秆内阻尼；风速、风压、风的脉动性、风速分布、地面粗糙度、地理位置，以及土壤松软程度。小麦生长成熟期风力作用下的运动微分方程：小麦生长成熟期风力作用下的运动规律表达式：更多还原

【Abstract】 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 stemτ_jh≈6.21MPa>the longitudinal sheering strength of stemτ_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 isτ=（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:更多还原