落叶松干燥过程中弱组元细胞开裂演化机理研究

Larix gmelini drying defects have closed relationship with the microscopic damage. The wood crack sourced from the weak point cells(WPE) is the macroscopical appearances.Therefore, it is significant that the cells fracture and evolution mechanism are investigated under the drying sress, to bulid the regulatory relationships between the drying parameters and cracks. In the study, supposing the wood as porous medium, the finite element method (FEM) numerical simulation model of weak point cells is bulit from perspectives of both wood micro-mechanics and the microscopic structure. The WEP shape database are establish by microscope observation. A yielding condition is fomulated by the classic shell theory under wood drying stress. The stress intensity factors are corrected by ESEM scanning. The heat and mass transfer mathematical model of hygroscopicity transient multi-field coupling is set up. By the research, the micro process of crack initiation, evaluation and propagation is analyzed from the stress cloud charts, the unload effect is calculated on the stress concentration, the regulatory relationships between the crack closure conditions and wood drying controlled parameters are studied. From the project, the experimental device is developed to study the drying stress in microscopic, the numerical simulation model is built by the multi-field coupling self-adaptive relations, the technical method of crack tip measured dynamically is studied, the theoretical research is set up to the crack closure and the wood drying parameters.

落叶松干燥缺陷与细观损伤有关，干燥裂纹是细胞开裂的宏观表现，细胞开裂始于弱组元细胞，研究干燥应力作用下弱组元细胞的开裂形成和演化机理，对于建立干燥裂纹与干燥参数之间的调控关系具有重要意义。因此，本项目拟从落叶松木材细胞微观构造及细观力学入手，通过显微观察识别弱组元细胞，建立弱组元细胞开裂形态库，应用经典壳体理论建立干燥应力作用下的弱组元细胞开裂屈服条件，通过ESEM扫描观测对比修正应力强度因子，选用吸湿性瞬态多场耦合传热传质数学模型，建立含弱组元细胞多孔有限元数值分析模型。通过本项目的研究，可以从模型应力云图分布形态分析木材微裂纹的萌生、演化和扩展机制，分析应力集中度的卸载效应，研究裂缝重新闭合与环境参数调控关系。研究成果为细观研究干燥应力提供科学实验装置，为建立多场耦合自适应关系提供数值分析模型，为动态测量裂尖开裂参数提供技术手段，为干燥参数控制裂纹逆过程提供应用基础研究。

从立项开始，我们都是严格按照申请书年度计划进行相关研究，我们在预订时间内以落叶松木材为研究对象，拟从细胞的微观构造及细观力学角度入手，通过显微观察识别弱组元细胞，研究细胞解剖特征量的检测方法，在扩展有限元仿真研究中考虑弱组元细胞微观结构损伤，应用经典理论建立干燥应力作用下弱组元细胞壁开裂的屈服条件，对比修正弱组元细胞应力开裂应力强度因子，建立具有一定规模组织的多孔力学模型。数值分析选用瞬态多场耦合传热传质数学模型，建立热湿应力本构方程，研究干燥应力作用下落叶松木材弱组元细胞的开裂、演化和形成机理。