动载作用下木片断裂形貌特征与分形力学模型的研究
发布时间：2018-07-18 16:50
【摘要】：纤维板生产中,木片在热磨机磨片的动载作用下分离成纤维。木片断裂的形貌特征、定量描述方法和木片断裂过程中强度薄弱的方向以及能量消耗的影响因素,对热磨机纤维分离机理及其磨片优化设计研究有着重要的影响作用,是此领域研究的前沿课题之一。本文利用分形理论和断裂力学理论,主要研究了木片受剪切、冲击载荷断裂解离的形貌特征、力学性能和分形特征,通过建立动载作用下木片断裂的分形力学模型,研究了木片断裂时能量消耗的影响因素和规律。本文以5种有代表性的针阔叶木材为试验材料,通过剪切断裂试验,获取各树种试件断口的图像和断裂所需的力；运用分形理论对试件的断裂方向、断裂表面形态、力学特性和分形特征进行分析,获得断口的分形维数及其与分形曲线的关系;计算分析各树种试件的抗剪强度,得到其抗剪强度薄弱的方向和条件,探讨各树种试件的抗剪强度与其断口分形维数之间的相关性。通过对试件进行冲击断裂试验,获取各树种试件断口的图像和断裂所需的能；运用分形理论对试件的断裂方向、断裂表面形态、力学特性和分形特征进行分析,获得断口的分形维数及其与分形曲线的关系；计算分析各树种试件的冲击韧性,得到其冲击韧性薄弱的方向,探讨各树种试件的冲击韧性与其断口分形维数之间的相关性。从热磨机磨片各分区采集试验的纤维样本,运用分形理论建立了木片研磨过程中,各分区纤维的长度、直径与纤维距磨盘外边沿距离的双对数线性回归模型,模型表明,木片研磨分离过程中,纤维长度或直径的变化具有分形性；通过对各分区纤维长度和直径分形维数的分析,揭示了研磨解离纤维时,磨片各分区纤维分离活动的特征和磨损趋向。利用分形和断裂力学理论建立木片断裂的分形断裂模型和动载作用下分形力学模型;通过对木片断裂分形断裂模型和动载作用下分形力学模型的曲线分析,获得木片断裂时裂纹的初始条件和动载作用下木片断裂时对能量消耗的影响及变化规律,为热磨机及磨片的结构和参数设计提供了理论依据。本文通过对材料断口分形维数计算方法的研究分析,提出了一种利用三维扫描计算材料断口分形维数的新方法,并获得了授权发明专利(ZL201310185200.4)；此方法具有精度高、不受码尺限制、可重复测量计算的特点,为分形维数的计算寻找到新的途径。动载作用下木片断裂形貌特征与分形力学模型的研究,也为热磨法纤维分离机理的深入研究,实现节能降耗,提高热磨纤维质量提供理论依据和应用实践,具有重要理论意义和实际应用价值。
[Abstract]:In the production of fiberboard, wood chips are separated into fibers under the action of the dynamic load of the grinder. The morphology characteristics, quantitative description method, the direction of weak strength and the influencing factors of energy consumption in the process of wood chip fracture have important effects on the separation mechanism of fiber and the optimum design of the mill. It is one of the frontier research topics in this field. In this paper, fractal theory and fracture mechanics theory are used to study the morphology, mechanical properties and fractal characteristics of fracture dissociation of wood subjected to shear and impact loading. The influencing factors and rules of energy consumption during the breaking of wood chips were studied. In this paper, five kinds of representative coniferous broadleaved wood were used as experimental materials. Through shear fracture test, the fracture images and the force needed for fracture of each tree species specimen were obtained, and the fracture direction and fracture surface morphology of the specimen were analyzed by fractal theory. The fractal dimension of fracture surface and its relation with fractal curve are obtained by analyzing the mechanical and fractal characteristics, the shear strength of each tree species specimen is calculated and analyzed, and the direction and conditions of weak shear strength are obtained. The correlation between the shear strength and the fractal dimension of the fracture surface of each tree species specimen was studied. Through the impact fracture test on the specimen, the fracture image of the specimen and the energy needed for the fracture are obtained, and the fracture direction, fracture surface morphology, mechanical properties and fractal characteristics of the specimen are analyzed by fractal theory. The fractal dimension of fracture surface and its relation with fractal curve are obtained, the impact toughness of each tree species specimen is calculated and analyzed, the direction of weak impact toughness is obtained, and the correlation between impact toughness and fractal dimension of fracture surface is discussed. Based on the fiber samples collected from each zone of the mill, a double-logarithmic linear regression model of fiber length, diameter and distance from the fiber to the outer edge of the disc is established by using fractal theory. The model shows that the fiber length, diameter and the distance between the fiber and the outer edge of the disc are linear regression models. The change of fiber length or diameter is fractal in the process of lapping and separation of wood pieces, and the fractal dimension of fiber length and diameter in each zone is analyzed to reveal that when lapping and dissociating the fiber, The characteristics and wear tendency of fiber separation activity in different subzones of grinding sheet. The fractal fracture model and the fractal mechanics model under dynamic load are established by using fractal and fracture mechanics theory, and the curve analysis of fractal fracture model and fractal mechanics model under dynamic load is carried out. The influence of the initial condition of the crack and the influence of the dynamic load on the energy consumption are obtained, which provides a theoretical basis for the structure and parameter design of the hot mill and the mill. Based on the research and analysis of the method of calculating the fractal dimension of material fracture, a new method for calculating fractal dimension of fracture surface of material by 3D scanning is proposed in this paper, and the patent of authorized invention (ZL2013101855200.4) is obtained, this method has high precision and is not limited by code size. The characteristics of repeatable measurement and calculation provide a new way for the calculation of fractal dimension. The study on fracture morphology and fractal mechanics model of wood chips under dynamic loading also provides theoretical basis and application practice for further study on separation mechanism of hot milling fibers, energy saving and consumption reduction, and improvement of quality of hot milling fibers. It has important theoretical significance and practical application value.
【学位授予单位】：东北林业大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：O346.1
本文编号：2132538
[Abstract]:In the production of fiberboard, wood chips are separated into fibers under the action of the dynamic load of the grinder. The morphology characteristics, quantitative description method, the direction of weak strength and the influencing factors of energy consumption in the process of wood chip fracture have important effects on the separation mechanism of fiber and the optimum design of the mill. It is one of the frontier research topics in this field. In this paper, fractal theory and fracture mechanics theory are used to study the morphology, mechanical properties and fractal characteristics of fracture dissociation of wood subjected to shear and impact loading. The influencing factors and rules of energy consumption during the breaking of wood chips were studied. In this paper, five kinds of representative coniferous broadleaved wood were used as experimental materials. Through shear fracture test, the fracture images and the force needed for fracture of each tree species specimen were obtained, and the fracture direction and fracture surface morphology of the specimen were analyzed by fractal theory. The fractal dimension of fracture surface and its relation with fractal curve are obtained by analyzing the mechanical and fractal characteristics, the shear strength of each tree species specimen is calculated and analyzed, and the direction and conditions of weak shear strength are obtained. The correlation between the shear strength and the fractal dimension of the fracture surface of each tree species specimen was studied. Through the impact fracture test on the specimen, the fracture image of the specimen and the energy needed for the fracture are obtained, and the fracture direction, fracture surface morphology, mechanical properties and fractal characteristics of the specimen are analyzed by fractal theory. The fractal dimension of fracture surface and its relation with fractal curve are obtained, the impact toughness of each tree species specimen is calculated and analyzed, the direction of weak impact toughness is obtained, and the correlation between impact toughness and fractal dimension of fracture surface is discussed. Based on the fiber samples collected from each zone of the mill, a double-logarithmic linear regression model of fiber length, diameter and distance from the fiber to the outer edge of the disc is established by using fractal theory. The model shows that the fiber length, diameter and the distance between the fiber and the outer edge of the disc are linear regression models. The change of fiber length or diameter is fractal in the process of lapping and separation of wood pieces, and the fractal dimension of fiber length and diameter in each zone is analyzed to reveal that when lapping and dissociating the fiber, The characteristics and wear tendency of fiber separation activity in different subzones of grinding sheet. The fractal fracture model and the fractal mechanics model under dynamic load are established by using fractal and fracture mechanics theory, and the curve analysis of fractal fracture model and fractal mechanics model under dynamic load is carried out. The influence of the initial condition of the crack and the influence of the dynamic load on the energy consumption are obtained, which provides a theoretical basis for the structure and parameter design of the hot mill and the mill. Based on the research and analysis of the method of calculating the fractal dimension of material fracture, a new method for calculating fractal dimension of fracture surface of material by 3D scanning is proposed in this paper, and the patent of authorized invention (ZL2013101855200.4) is obtained, this method has high precision and is not limited by code size. The characteristics of repeatable measurement and calculation provide a new way for the calculation of fractal dimension. The study on fracture morphology and fractal mechanics model of wood chips under dynamic loading also provides theoretical basis and application practice for further study on separation mechanism of hot milling fibers, energy saving and consumption reduction, and improvement of quality of hot milling fibers. It has important theoretical significance and practical application value.
【学位授予单位】：东北林业大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：O346.1
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