Study On Material Fracture Problems Considering Chemo-Mechanical Coupling

Multi-field coupling problems involving chemical processes exist widely in natural porous media,biological tissues,new functional materials.These processes may occur on different time scales and induce changes in material properties.A substantial understanding of interaction between chemical reactions and mechanical behaviors is of great significance,not only for optimization of the function and structure design of new materials,but also for the performance evaluation and prediction of traditional materials in the coupled fields.The transfer and transformation of mass,momentum and energy will occur under various stimuli such as temperature difference,electric potential difference,chemical potential gradient and stress.Moreover,the consumption and production of substances in chemical reactions will also cause changes in the concentration of material components,thereby affecting the mass transfer process and resulting in some impact on the microstructure and macroscopic properties of the materials.Based on the chemomechanical coupling problems in scientific research and industrial fields,theoretical modeling and related fracture problems are studied for the mass transfer,chemical reaction and mechanical coupling behavior of chemically active solids.The content of this paper is summarized as follows:(1)Based on the traditional Chemo-elasticity,the extent of reaction is introduced as an independent state variable,and a linear theoretical model considering the coupling of mass transfer,chemical reaction and deformation is derived.Based on the linear phenomenological law,the dynamic equations are constructed for the mass transfer and reaction progresses.Basic equations,governing equations and boundary conditions are given for the plane problem of isotropic materials.According to different time scales of diffusion and chemical reaction processes,two quasi-static problems are analyzed.(2)Based on the above theoretical model,the crack problem loaded on the crack surface under chemical equilibrium is studied.The governing equations are transformed into ordinary differential equations by Fourier transform,and the general solutions of the field variables are represented as the superposition of the basic solutions.By introducing the dislocation density functions,a Cauchy type singular integral equation corresponding to the problem is derived.The analytical form results can be obtained,and the direct integration method can also be used to obtain the numerical results.Furthermore,the singularity of the crack tip field has been studied and the stress intensity factor and concentration coefficient are obtained.The analytical and numerical results match well with each other.(3)The mode I and mode II crack problems in a finite thickness plate under steady state diffusion are investigated,and the flux conductivity is introduced to reflect the partial conductive of the crack surface.Through the superposition principle,the original problem was transformed into a crack surfaces loading situation.With the use of Fourier transform and introducing the dislocation density functions,the crack problem is reduced into a set of singular integral equations,which are solved numerically by Lobatto-Chebyshev method.The effects flux conductivity,crack geometric location and material parameters on chemical potential distribution and stress intensity factors are discussed in details.And the extreme results of special cases are discussed.(4)As for the fracture failure problems commonly found in metal oxide and cermet coatings,the interface cracking problem of functionally graded coating and substrate structure under chemo-mechanical loading is studied.With the assumption that the material parameters of the coating are distributed exponentially along the thickness direction and the substrate is homogeneous material,the corresponding governing equations for the problem are derived.The fracture problem is reduced to the solution of a set of singular integral equations,which can be solved numerically.Further,the influences of material inhomogeneous parameters,coating and substrate thickness on the chemical potential and equivalent diffusion stresses are discussed.Finally,the conclusion of this thesis and prospect of further work are given.