Digital Image Processing-Based Numerical Methods For Failure Process Analysis Of Rocklike Materials

Failure mechanism of rock and concrete materials is the focus and difficulty in mechanics investigations, material and engineering investigations. The investigations on failure process of rocklike materials are very important for evaluating the safe status and stability of geotechnical engineering and structures to take reasonable support measures and improving the designing level in rock engineering and underground engineering.Failure process of rock or concrete materials is a complicated non-equilibrium nonlinear progressive process. The nonlinear characteristic of macro-mechanical behaviors expressed in the process is derived from the heterogeneity of meso-struture. Under the same conditions, the overall stress and deformation of the specimen and the response of internal points are determined by the meso-structure and meso-material's properties. So how to measure the shape and distribution of meso-materials acutely should be studied. Only if these are integrated into numerical model and the parameters describing the constitutive law are determined, numerical study on mechanical performance and failure mechanism and criterion of geomaterials can be more overall and natural.In this thesis, digital image processing theory, the vector transformation method and the finite element method are integrated and microscopic damage mechanics theory and the theory of strength are synthesized to establish failure process analysis model based on realistic meso-scopic structures and study the realistic failure process of rocklike materials. The work in the present paper can be summarized as follows:1. Image feature of rocklike materials is analyzed in different color space and general-purpose digital image processing methods, including image segment, edge detection, image recognition and so on, are used to complete the characterization of the shape and distribution of meso-materials of rocklike materials.2. The relationship between the meso-structure characterized by digital image processing and the mesh of finite element method is determined in virtue of vector transformation. The damage evolution equations and constitutive law are formulated by integrating microscopic damage mechanics and the theory of strength, and numerical model based on the realistic meso-structure is established.3. Digital image processing software for the image of rocklike materials is developed in Visual C++ language on Microsoft Visual Studio and the data interface for finite element method is realized. Finite element method is applied to obtain the stress and strain of the model. A finite element program is developed in FORTRAN language on PowerStation. Digital image based failure process analysis code for rocklike materials is developed in Visual C++ language in Windows XP operation system by introducing the meso-structure characterized by DIP.4. The effect of meso-structure on mechanical performance and failure process is investigated in detail. The sensitivity of strength and elastic modulus on meso-structure is analyzed and the mechanism of axial splitting fracture subjected to uniaixal compressive load is revealed. The reason for part mechanical effect and the effect of confining pressure on fracture angle are studied.5. Three-phase composite meso-structure of concrete is measured by digital image processing methods combining edge detection and image segment. Edge detection method is used to measure the shape and distribution of interface transition zone and image segment method is used to measure those of aggregate. And further the effect of shape and distribution of aggregate on stress distribution and crack initiation and propagation is studied.6. On some hypothesis, by using serial sectioning method, section images of material are captured at intervals of some depth, and then two-dimensional meso-structure represented by section images is overlapped to reconstruct three-demensional realistic meso-structure of the sample. Three-dimensional numerical model based on realistic meso-structure is established by combining Digital Image Processing Software (abbreviated as DIPS) and three-dimensional rock failure process analysis code (abbreviated as RFPA3D). The effect of interfacial transition zone on crack propagation is primarily investigated by parallel computing technique.