【摘要】：玉米秸稈作為一種重要的生物質(zhì)資源,在資源日益匱乏的經(jīng)濟(jì)時(shí)代,逐漸被大家所重視。由于玉米秸稈具有復(fù)雜多樣的內(nèi)部結(jié)構(gòu),導(dǎo)致其具有獨(dú)特的個(gè)體差異,從而呈現(xiàn)出不同的力學(xué)性能,直接影響它的利用。深入研究玉米秸稈各組分的力學(xué)性能及其差異,并建立相應(yīng)的力學(xué)模型,探討外載荷作用下的力學(xué)特性變化規(guī)律,為其深度綜合利用和預(yù)處理加工機(jī)械設(shè)計(jì)提供基礎(chǔ)的理論依據(jù)。針對(duì)玉米秸稈的力學(xué)特性理論分析和數(shù)學(xué)建模這一較為困難的問(wèn)題,在對(duì)玉米秸稈的生物物理力學(xué)特性進(jìn)行研究的基礎(chǔ)上,利用離散元方法建立玉米秸稈離散元力學(xué)模型,包括:玉米秸稈外皮、內(nèi)穰的剪切和拉伸力學(xué)特性離散元模型;單根玉米秸稈的徑向壓縮、彎曲力學(xué)特性離散元模型和玉米秸稈集合體的打捆力學(xué)特性離散元模型等。論文圍繞玉米秸稈離散元模型的建立,對(duì)玉米秸稈物理和力學(xué)特性進(jìn)行了研究,取得的主要研究成果如下:(1)測(cè)試了玉米秸稈基本物料特性參數(shù),得到:玉米莖稈的平均直徑為16.14±4.05mm,平均外皮厚度為0.9mm,外皮、內(nèi)穰和整體的平均密度分別為1.12、0.66和1g/cm3,同時(shí)用圖像處理的方法得到玉米秸稈維管束的橫截面直徑為0.15mm,用烘干法測(cè)得新鮮玉米秸稈含水率為80%,風(fēng)干玉米秸稈的含水率為8%。(2)建立了玉米秸稈外皮軸向剪切力學(xué)特性的離散元模型,同時(shí)進(jìn)行了剪切測(cè)試與模擬對(duì)比。剪切測(cè)試結(jié)果表明:外皮平均剪切強(qiáng)度為3.00MPa,平均彈性模量為0.23GPa;外皮軸向剪切強(qiáng)度和彈性模量隨節(jié)間位置升高而降低;含水率和品種對(duì)剪切強(qiáng)度和彈性模量均無(wú)影響。模擬結(jié)果表明:對(duì)玉米秸稈外皮軸向剪切模型加載后模擬的力學(xué)特性與實(shí)際測(cè)試力學(xué)特性相似;模擬的破壞過(guò)程中的載荷—位移圖線與測(cè)試實(shí)測(cè)曲線相一致;獲得了外皮維管束間的離散元模型參數(shù),主要參數(shù)s-bond和kn的取值范圍分別為0.14-0.32 N和1×106-1.2×107N·m-1。(3)建立了玉米秸稈外皮和內(nèi)穰進(jìn)行拉伸力學(xué)特性的離散元模型,同時(shí)進(jìn)行了拉伸測(cè)試與拉伸模型模擬對(duì)比。拉伸測(cè)試結(jié)果表明:秸稈外皮拉伸具有塑性材料的特征,在新鮮狀態(tài)下,抗拉強(qiáng)度為131.1?48MPa,彈性模量為22.93?13GPa;風(fēng)干狀態(tài)下,抗拉強(qiáng)度為113.42?40MPa,彈性模量為15.71?6GPa;玉米秸稈內(nèi)穰拉伸具有脆性材料的特征,在新鮮狀態(tài)下,抗拉強(qiáng)度為1.09?0.27MPa,彈性模量為0.06?0.02GPa;在風(fēng)干狀態(tài)下,抗拉強(qiáng)度為0.86?0.67MPa,彈性模量為0.12?0.07GPa;玉米秸稈的拉伸強(qiáng)度和彈性模量隨節(jié)間位置升高而降低,隨含水率的增加而增加,拉伸強(qiáng)度受到品種的一定影響,拉伸彈性模量卻不受品種影響。秸稈內(nèi)穰的拉伸強(qiáng)度,新鮮秸稈大于風(fēng)干秸稈;而對(duì)于拉伸彈性模量,則為風(fēng)干秸稈大于新鮮秸稈;節(jié)間位置和品種對(duì)內(nèi)穰的拉伸強(qiáng)度和彈性模量無(wú)顯著影響。離散元模型模擬結(jié)果表明:玉米秸稈外皮和內(nèi)穰組織的離散元模型軸向拉伸力學(xué)特性曲線,以及破壞現(xiàn)象,均與測(cè)試特性相似;并分別獲得外皮軸向模型主要力學(xué)性能參數(shù)bondstrength為85.64-131.11 Pa·m-1(新鮮秸稈)和80.53-113.42 Pa·m-1(風(fēng)干秸稈),pb-kn為4.58×1013-1.05×1014 Pa·m-1(新鮮)和3.79×1013-6.97×1013 Pa·m-1(風(fēng)干),以及內(nèi)穰離散元模型的離散元參數(shù)kn為0.5×106-1.5×106 N·m-1(風(fēng)干)和1.6×106-3×106 N·m-1(新鮮),ks為1.0×106 N·m-1,n-bond為5-30 N(風(fēng)干)和35-50N(新鮮),s-bond為10-20N(風(fēng)干)和40-50N(新鮮)。(4)建立了單根玉米秸稈的徑向壓縮力學(xué)特性離散元模型,同時(shí)進(jìn)行了徑向壓縮測(cè)試與模擬結(jié)果的對(duì)比。模型的模擬結(jié)果表明:得出得到虛擬的載荷-位移曲線主要包括彈性階段、破壞階段和強(qiáng)化階段,并分析了虛擬的壓縮破壞現(xiàn)象和壓縮過(guò)程中的微觀力學(xué)響應(yīng);將測(cè)試結(jié)果與模擬結(jié)果對(duì)比分析,認(rèn)為模型合理,與實(shí)際材料吻合,并通過(guò)模型分析出玉米秸稈受壓狀態(tài)時(shí)內(nèi)部結(jié)合機(jī)理。(5)建立了單根玉米秸稈的彎曲力學(xué)特性離散元模型,同時(shí)進(jìn)行了彎曲測(cè)試與模擬結(jié)果對(duì)比。模擬結(jié)果表明:彎曲力學(xué)特性曲線主要包括彈性階段和粘彈性階段,并分析了虛擬的彎曲破壞現(xiàn)象和壓縮過(guò)程中的微觀力學(xué)響應(yīng);將測(cè)試結(jié)果與模擬結(jié)果對(duì)比分析,認(rèn)為模型合理,與實(shí)際材料吻合,并通過(guò)模型分析出玉米秸稈彎曲破壞時(shí)內(nèi)部結(jié)合機(jī)理。(6)建立了多根玉米秸稈的打捆力學(xué)特性離散元模型,并進(jìn)行虛擬打捆模擬與測(cè)試結(jié)果對(duì)比。打捆測(cè)試得到:捆扎密度與打捆松緊度的關(guān)系為二次曲線關(guān)系;秸稈打捆的繩索張力與捆扎直徑的關(guān)系為指數(shù)函數(shù)關(guān)系。虛擬打捆模擬得到:虛擬打捆力學(xué)性能曲線與測(cè)試曲線相似;虛擬打捆模擬的載荷與圓捆半徑呈現(xiàn)指數(shù)函數(shù)關(guān)系。測(cè)試結(jié)果與模型模擬趨勢(shì)相同,表明離散元模型可用于玉米秸稈加工利用機(jī)械設(shè)計(jì)中的物料力學(xué)特性模擬。
[Abstract]:As an important biomass resource, the corn straw is gradually being paid attention to by the economic times of the increasingly scarce resources. Because the corn straw has a complex and diverse internal structure, it has unique individual difference, thus presenting different mechanical properties and directly affecting the utilization of the corn straw. In this paper, the mechanical properties and the difference of each component of the corn stalk are studied deeply, and a corresponding mechanical model is established to study the change rule of the mechanical property under the action of the external load, which provides a theoretical basis for the comprehensive utilization of the maize straw and the mechanical design of the pre-treatment process. Based on the research of the physical and mechanical properties of the corn straw, the discrete element method of the maize straw is established by means of the discrete element method, which includes the following steps: A discrete element model of shear and tensile mechanical properties of a single corn straw, a discrete element model of the radial compression of a single corn straw, a discrete element model of a bending mechanical property and a bundling mechanical characteristic discrete element model of the corn straw aggregate, and the like. The paper studies the physical and mechanical properties of the maize straw, and the main research results are as follows: (1) The basic material property parameters of the corn straw are tested, and the average diameter of the corn stalk is 16.14-4.05mm. The average density of the outer skin is 0.9mm, the average density of the outer skin, the inner layer and the whole is 1.12, 0.66 and 1 g/ cm3 respectively, and the cross section diameter of the corn straw vascular bundle is 0.15 mm by the method of image processing, and the water content of the fresh corn straw is 80% by the drying method, and the moisture content of the air-dried corn straw is 8%. (2) The discrete element model of the axial shearing and mechanical properties of the corn straw outer skin is established, and the shear test and the simulation comparison are also carried out. The results of the shear test show that the average shear strength of the skin is 3.00 MPa, the average elastic modulus is 0.23 GPa, the axial shear strength and the elastic modulus of the outer skin decrease with the increase of the position of the internode, and the water content and the variety have no effect on the shear strength and the elastic modulus. The simulation results show that the mechanical characteristics of the simulation after loading the axial shear model of the corn straw outer skin are similar to that of the actual test mechanics, and the load displacement curve in the simulation is in line with the measured curve of the test, and the discrete element model parameters between the outer sheath and the pipe bundle are obtained. The values of s-bond and kn are 0.14-0.32 N and 1-106-1.2-107 N 路 m-1, respectively. (3) The discrete element model of the tensile and mechanical properties of the outer skin and the inner surface of the maize straw was established, and the comparison of the tensile test with the tensile model was also carried out. The tensile test results show that the tensile strength is 131.1-48MPa, the elastic modulus is 22.93-13GPa in the fresh state, the tensile strength is 113.42-40MPa, the elastic modulus is 15.71-6GPa, and the tensile strength of the corn straw is characterized by the brittle material. in the fresh state, the tensile strength is 1.09-0.27MPa and the elastic modulus is 0.06-0.02GPa; in the air-drying state, the tensile strength is 0.86-0.67MPa, the elastic modulus is 0.12-0.07 GPa, the tensile strength and the elastic modulus of the corn straw are reduced along with the increase of the position of the internode, and the elastic modulus is increased with the increase of the water content, The tensile strength is affected by the variety, and the tensile elastic modulus is not affected by the variety. The tensile strength of the straw in the straw is higher than that of the air-dried straw, and for the tensile elastic modulus, the air-dried straw is larger than the fresh straw, and the internode position and the variety have no significant influence on the tensile strength and the elastic modulus of the inner layer. The simulation results of the discrete element model show that the mechanical characteristic curve of the axial tensile and mechanical properties of the discrete element model of the corn straw outer skin and the inner-shell tissue are similar to those of the test characteristics. And the main mechanical property parameters of the outer skin axial model are 85.64-131.11 Pa 路 m-1 (fresh straw) and 80.53-113.42 Pa 路 m-1 (air-dried straw), and the pb-kn is 4.58-1013-1.05-1014 Pa 路 m-1 (fresh) and 3.79-131013-6.97-1013 Pa 路 m-1 (air-dried). And the discrete element parameter kn of the internal discrete element model is 0.5-106-1.5-106N 路 m-1 (air-dried) and 1.6-106-3-106N 路 m-1 (fresh), ks is 1.0-106N 路 m-1, n-bond is 5-30N (air-dried) and 35-50N (fresh), s-bond is 10-20N (air-dried) and 40-50N (fresh). (4) The discrete element model of the radial compression and mechanical properties of a single corn straw is established, and the comparison of the radial compression test with the simulation results is carried out. The simulation results of the model show that the virtual load-displacement curve mainly includes the elastic phase, the failure stage and the strengthening phase, and the virtual compression failure phenomenon and the micro-mechanical response in the compression process are analyzed, and the test results are compared with the simulation results. It is considered that the model is reasonable and is in good agreement with the actual material, and the internal binding mechanism of the corn straw under pressure is analyzed through the model. (5) A discrete element model of the bending and mechanical properties of a single corn straw is established, and the comparison of the bending test with the simulation results is carried out. The simulation results show that the curve of bending mechanics mainly includes the elastic phase and the viscoelastic phase, and the virtual bending failure and the micro-mechanical response in the compression process are analyzed. The results of the test and the simulation results are compared and analyzed, and the model is considered to be reasonable and consistent with the actual material. And the internal binding mechanism of the corn straw bending and destruction is analyzed through the model. And (6) establishing a discrete element model of a bundling mechanical property of a plurality of corn straws, and comparing the virtual bundling simulation with the test result. The relationship between the binding density and the bundling diameter is the quadratic curve, and the relationship between the rope tension and the binding diameter of the straw bundle is an exponential function. The virtual bundling simulation results in that the virtual bundling mechanical property curve is similar to the test curve, and the load of the virtual bundling simulation is in exponential function relation with the radius of the round bundle. The result of the test is the same as that of the model, which indicates that the discrete element model can be used to simulate the mechanical properties of the material in the mechanical design of the corn straw processing.
【學(xué)位授予單位】：西北農(nóng)林科技大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2017
【分類號(hào)】：TQ914.3

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