Study On Mechanics Of Instability And Reinforcement With Damage Localization Of Rock-like Materials

The localized band with intense deformation is caused by the development and coalescence of micro-cracks in loaded rock-like geomaterials. The process of deformation of rock-like geomaterials is companied by degradation of mechanical behaviors and whole loaded capability. The farther development of intense deformation caused structural whole failure:To prevent the deformation and failure, the pre-stress anchor cable is used to reinforce jointed rock mass. However the mechanics of Instability and Reinforcement with Damage Localization is very complex and there are some issues that have not been well solved in engineering practice. An intensive study is required for consideration on mechanics of instability and reinforcement with damage localization of rock-like geomaterials. Therefore the analysis of damage bifurcation and instability of rock-like geomaterials, the relationship between strain softening model and characteristic point of localized band, mechanism of reinforcement on crack prevention of jointed rock mass, effect of non-local models with different types of functions on stress-strain field at crack tip, the bifurcation and instability of plastic softening model and its finite element implementation are mainly concerned in this dissertation. The main research and results involved in the dissertation includes the following parts.1. The process of deformation of rock-like geomaterials is accompanied with nonlinear features of obvious stiffness degradation and volumetric dilatancy. In analyzes of bifurcation and instability of materials the two nonlinear deformation features of elasto-plasticity and damage should be taken into consideration simultaneously. Therefore, under the condition of isotropic damage, in this paper the damage variation and damage loaded-unioaded function are taken into consideration in the analysis of discontinuous bifurcation of elastic-plastic model. The variation characteristics such as stiffness degradation and initial Poisson's ratio increasing are taken into account, then the critical hardening modulus and localized orientation angle of materials with consideration of damage degradation and volumetric dilatancy are set up through theoretical derivation. The relationship of localized orientation angle and critical hardening modulus depended on degree of damage and initial Poisson's ratio of rock is explored. Comparative analyzes are conducted to study the bifurcation of uniaxial compression-tension samples under the conditions of plane stress and plane strain.2. The relations of stress-strain is different in the process of deformation owing to the differences of mechanical parameters, the characteristic of the strain softening phase and load under experimental conditions. And the fracture process of samples is not easy to observe. In the paper the damage critical curved surface is derived considering the related effect of isotropic damage and degradation of cohesion and internal friction angle of Mohr-Coulomb strength law. The characteristics of axial stress-displacement curve, axial-lateral displacement curve, networks of shear bands and the change with degree of damage, confining pressure, poisson's ratio are investigated numerically by monitoring the stress-displacement values in the process of deformation of samples under plane strain and different initial conditions. Furthermore, the law of the localized orientation of samples in different deformation characteristic point with the change of confining pressure and degree of damage is derived by non-associative damage Mohr-Coulomb yield law. The localized orientation is Compared with that obtained by numerical simulation.3. The fracture orientation of crack of different angle, the mini-plastic zone displacement near crack tip, the effective displacement of rock-bridge between con-liner close cracks tips after fracture are derived by the rule of mini-plastic zone displacement near crack tip from strain viewpoint. A new method of equivalent pre-stress is suggested to simulate the mechanism on reinforcement of pre-stress anchor cable by finite element method. The mechanism and distortional character of consolidated segment and rock mass under single anchor cable and multi anchor cables is analyzed. Some attentions is indicated when reinforcement by pre-stress anchor cable. The mechanism of reinforcement of pre stress anchor cable on crack prevention of jointed rock mass is studied by the fracture rule of mini-plastic zone displacement. The extending mechanism of con-linear cracks of different angle is analyzed under different consolidation condition.4. The essential characteristics together with optimum selection of weighted functions is analysed in the non-local theory. Therefore, the influence area of the weighted functions and its dependency on internal length scale are examined for a number of commonly used types of weighted functions. To eliminate the singular of stress and strain field near crack tip, the stress and strain field in the neighborhood of the tip ofâ… -â…¡mixed mode crack are analyzed in compare with local strain of different orientation near crack tip by using the non-local theories based on different types of weighted functions. Furthermore, the effects of non-local theory of different types of the weighted functions and the stress intensity factor K_â… and K_â…¡on the all components of stresses and strains at the crack tip are investigated.5. Considering deficiency of linear softening model which cannot reproduce distortion complexity of geo-material, a nonlinear and non-local model of plastic-strain gradient is presented by incorporating the nonlinear and non-local theory with the theory of plastic strain gradient. A nonlinear and non-local model is proposed by using an exponential pattern of strain softening and weighted by Gaussian distribution function while the effect of plastic strain gradient is taken into account. The mechanical characteristics of isotropic bar under uniaxial tension are examined by the proposed model and analysis results of the proposed model are compared with those of the linear-softening model.