Research On The Fracture Behavior Of Solid Electrolyte Under The Coupled Mechanical And Chemical Fields

The solid electrolyte material is the most important component of the solid oxide fuel cell.Ionic conductivity and mechanical strength of the solid electrolyte material is the focus of research.The reason why the solid electrolyte has conductivity is the presence of oxygen vacancies.Oxygen vacancy provide the transfer way for oxygen ion.But considered as a kind of point defect,the oxygen vacancy will impact on material mechanical properties inevitably.In particular,when the electrolyte contains the crack,the crack-tip stress field would be influenced by a lot.This will affect the redistribution of oxygen vacancy,which will affect the performance of cell system.Hence,this article will research the relationship between the oxygen vacancy and the crack-tip stress field by finite element method.In addition,the fracture toughness under different conditions will be analyzed by molecular dynamics method.First,the basic theory of the finite element method is described.In the thesis,the coupling equation of the force field-chemical field is deduced and the discrete processing of the equation is carried out by using the finite element method.It is found that when the micro-cracks are present in the electrolyte,the stress field of the crack tip has an induction effect on the distribution of oxygen vacancies,and this induction is proportional to the value of the crack tip stress field.Then,the diffusion behaviors of oxygen ions in the electrolyte are studied by using molecular dynamics simulations.The doping concentration,temperature and load were used as variables to simulate the Mean Square Displacement?MSD?of oxygen ions in GDC.The diffusion coefficient is solved by simulation results.The oxygen ion diffusion under different conditions was obtained and the corresponding analysis was carried out.Finally,the CeO₂ and GDC under uniaxial tensile loading were simulated by molecular dynamics method.The Young's modulus was obtained by analyzing the stress-strain curve,and the Young's modulus of CeO2 and GDC under different conditions were summarized.Based on the Young's modulus,the fracture toughness of CeO₂ macroscopic isotropic was calculated according to the basic theory of fracture mechanics.The surface energy of CeO2 and GDC is simulated and the variation law of fracture toughness is given when considering crystal anisotropy.The fracture toughness of GDC is obviously smaller than the fracture toughness of CeO₂,and this difference is related to the doping concentration,temperature and crystal orientation.