固体电解质在力—化学场耦合作用下的断裂行为研究

发布时间：2018-04-19 17:54

本文选题：力场-化学场耦合 + 电解质GDC　；参考：《哈尔滨工业大学》2017年硕士论文

【摘要】：固体氧化物燃料电池(SOFC)中最重要的组成部分是固体电解质,固体电解质的离子电导率和机械强度是现今科研人员关注和研究SOFC的重点。固体电解质具有离子导电性的原因是氧空位的存在为氧离子的扩散传递提供了途径,而氧空位作为一种点缺陷来考虑时,其存在必然会对材料的机械性能产生影响。尤其是当电解质中存在裂纹时,裂纹尖端应力场会发生巨大的改变,这必然会影响到氧空位的重新分布,导致电池系统受到影响。因此,本文首先利用宏观有限元方法对力场-化学场耦合作用下电解质GDC(氧化钆掺杂的氧化铈)中裂纹尖端应力场和氧空位的关系进行了研究分析,然后采用微观分子动力学方法对不同条件下的电解质GDC断裂韧度进行了计算分析,为固体氧化物燃料电池中的固体电解质的安全设计与寿命评估提供了参考价值。本文首先从宏观连续介质力学角度,推导了力场-化学场耦合方程,并利用有限元思想对方程进行离散处理。通过数值模拟计算发现当电解质材料中有微裂纹存在时,裂纹尖端应力场对氧空位的分布具有吸引诱导作用,且这种吸引诱导作用会随裂纹尖端应力场的增大而增强。然后从微观分子动力学(MD)角度对电解质GDC中氧离子的扩散进行了MD模拟,分别以掺杂浓度、温度和载荷作为变量,对GDC中氧离子的均方位移进行模拟,通过理论计算获得扩散系数,得到不同条件下氧离子扩散的情况并进行了相应的分析。最后应用MD方法建立了CeO_2和GDC的模型并对其进行了单轴拉伸模拟,通过对应力-应变曲线的分析得到杨氏模量,并对不同条件下CeO2和GDC的杨氏模量变化规律进行了总结。基于杨氏模量的求解,根据断裂力学基本理论计算了CeO_2宏观各向同性时的断裂韧度。接下来对CeO_2与GDC的表面能进行了模拟计算,给出了考虑晶体各向异性时的断裂韧度的变化规律,并将二者的断裂韧度进行比较,发现GDC断裂韧度明显小于CeO_2的断裂韧度,且这种差异与掺杂浓度、温度和晶向都有关系。
[Abstract]:Solid electrolyte is the most important component of solid oxide fuel cell (SOFC). The ionic conductivity and mechanical strength of solid electrolyte are the focus of researchers' attention and research on SOFC.The reason for the ionic conductivity of solid electrolytes is that the existence of oxygen vacancies provides a way for the diffusion and transfer of oxygen ions, and when oxygen vacancies are considered as a point defect, the existence of oxygen vacancies will inevitably affect the mechanical properties of the materials.Especially when there is a crack in the electrolyte, the stress field at the crack tip will change greatly, which will inevitably affect the redistribution of oxygen vacancies, which will affect the battery system.Therefore, the relationship between the stress field at crack tip and oxygen vacancy in GDCelectrolyte under the coupling of force field and chemical field is studied by means of the macroscopic finite element method (FEM), and the relationship between the stress field at the crack tip and the oxygen vacancy in the electrolyte GDC (gadolinium oxide doped cerium oxide) is studied.Then the fracture toughness of electrolyte GDC under different conditions is calculated and analyzed by micromolecular dynamics method, which provides a reference value for the safe design and life evaluation of solid electrolyte in solid oxide fuel cell (SOFC).In this paper, the coupling equations of force field and chemical field are derived from the viewpoint of macroscopic continuum mechanics, and the equations are discretized by finite element method.The numerical simulation results show that the stress field at the crack tip has an attractive effect on the distribution of oxygen vacancies when there are microcracks in the electrolyte material, and this attraction inducement will increase with the increase of the stress field at the crack tip.Then the MD simulation of oxygen ion diffusion in electrolyte GDC was carried out from the viewpoint of micro molecular dynamics (MD). The mean square displacement of oxygen ion in GDC was simulated by using doping concentration, temperature and load as variables, respectively.The diffusion coefficient is obtained by theoretical calculation, and the diffusion of oxygen ions under different conditions is obtained and analyzed accordingly.Finally, the models of CeO_2 and GDC are established by using MD method, and the uniaxial tensile simulation is carried out. The Young's modulus is obtained by analyzing the stress-strain curves, and the variation law of Young's modulus of CeO2 and GDC under different conditions is summarized.Based on the solution of Young's modulus, the fracture toughness of CeO_2 macroscopic isotropy is calculated according to the basic theory of fracture mechanics.Then, the surface energy of CeO_2 and GDC is simulated and calculated, and the variation law of fracture toughness considering crystal anisotropy is given. It is found that the fracture toughness of GDC is obviously smaller than that of CeO_2, and the fracture toughness of GDC is obviously smaller than that of CeO_2.The difference is related to the doping concentration, temperature and crystal direction.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O346.1;TM911.4

【参考文献】