Advances in Fracture and Materials Behavior

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Authors: Wei Shen Zhu, Bin Sui, Wen Tao Wang, Shu Cai Li
Abstract: Two-phase modelling testing was performed to study the shear strength of rock bridges of jointed rock mass in this paper. The failure process of rock sample containing multiple collinear cracks was observed. Based on theory of fracture mechanics and analytical method, a rock-bridge failure model was proposed and the expression of shear strength was derived. Comparison of calculated shear strength and the model test results was made and they agree well.
Authors: Hong Chang Qu, Guo Rong Chen
Abstract: A three-phase composite material specimen consisting of aggregates, mortar matrix and their bonding material is created through the Monte-Carlo method. The Mazars isotropic damage evolution model is used to describe the meso-mechanics damage deterioration of concrete. And the finite element method is adopted to simulate respectively the uniaxial compression numerical models of two, three and full graded specimens with sphere and polyhedron aggregates. Following are the conclusions from the test results: the ultimate load capacity of arbitrary polyhedron aggregate specimen is greater than that of the sphere one of the same grade; the size effect law exists in these numerical models of concrete specimens; the stiffness of the polyhedron aggregates’ specimen of the same grade is greater than that of the sphere ones’, and the softening curves of the sphere aggregate model are easier than those of the polyhedron by comparison in the softening phase of stress-strain curves.
Authors: Li Song, Tao Xu, Ying Yan Xie
Abstract: Rock is a typical non-homogeneous material. The behavior of a rock block under compression and the process of micro-fracture in that block are phenomena of considerable interest in understanding the strength characterization of brittle rock. In this study, the effect of the non-homogeneity on limit bearing capacity of rock block based on Rock Elasto-Plastic Failure Process Analysis code (REPFPA) are simulated and investigated. Numerical simulations find out that there exists a functional relation between the heterogeneity coefficient and the limit bearing capacity of rock block. For specimens with the same heterogeneity, however, the numerical simulations show that the failure modes depend greatly on the crack initiation location, which is found to be sensitive to the local disorder features within the specimen. In addition, the characteristics of acoustic emissions with the changing of heterogeneity coefficient were also found. These identifications are crucial for better understanding and interpreting the experimental results and consequently, improve our concepts in design or analysis of rock engineering structures.
Authors: Xiao Yan Liu, Cheng Yuan Zhang, Quan Sheng Liu
Abstract: Task_D of the DECOVALEX_THMC project focus on predictive analysis of the long-term coupled processes(up to 10,000 years) in two generic repositories, FEBEX type and Yucca Mountain Project type for comparison. To better understand the coupled THM processes and their influence on the system behavior, we have introduced a set of generic coupled THM governing equations. Basing on these equations, we develop simplified models according to given Task_D model inception phase request. Boiling model and empirical bentonite swelling model are introduced into general simulation which makes model more practical. Our numerical code FRT-THM upon this practical models is developed and used in two BMT case study of Task_D. Simulation results are shown and verified in the 3rd and 4th workshop of DECOVALEX_THMC in 2005. There is a good agreement with results of different participant teams which enhances confidence in prediction of coupled THM processes.
Authors: Quan Sheng Liu, Guang Miao Xu, Yue Xiu Wu
Abstract: Considering the influence of phase change and temperature variation on the physical and mechanical properties of low-temperature rock in cold regions, the mathematical model for the Thermo-Hydro(TH) coupled problem is proposed based on the theory of convective heat transfer for porous medium. In this model, the influence of moisture migration on heat conduction in rock is taken into account, as well as the influence of temperature gradient on the seepage. The involved parameters are determined according to the related equations given in this paper. Then the finite element model of a gas transmission pipeline in cold region is established using the proposed mathematical model. By selecting suitable boundary conditions, initial conditions and heat computation parameters, the freezing problem of low-temperature rock surrounding the pipeline is analyzed. The calculated values of the temperature field and the measured data are basically consistent, which indicates that the proposed TH coupling model for rock in cold regions is reasonable and reliable.
Authors: Yun Feng Li, Yu Hua Lu
Abstract: Using environment simulation technology, simulation testing for environmental behavior of concrete structure could be developed. Concrete durability experiment and its relative theory research would be progressed, and it play an important role in ensuring security and durability of structures. Tailoring environment tests are discussed in the paper, as well as determining all kinds of environmental factors of durability experiment and constructing several coupling environment. Simulation tests for environmental behavior of concrete structure will be developed based on the study.
Authors: Xiao Jing Li, Wei Min Yang, Wei Shen Zhu, Shu Cai Li, Ai Hua Sun
Abstract: The jointed rock mass distributed in the nature widely and its mechanical characteristic influenced the stability of the rock engineering badly. The cracks propagated and coalesced each other and macroscopic failure happened. Bolts were a kind of effective reinforcement instrument and they could prevent the cracks from propagating. However, the anchoring mechanism of bolts was not realized clearly and their reinforcement could not be reflected effectively in the numerical simulation yet. Based on the damage mechanics, a constitutive relation and damage equation of anchored jointed rock mass were presented in this paper. With a project application, the model was proved to be feasible one.
Authors: Quan Sheng Liu, Bin Liu, Wei Gao
Abstract: This paper introduces the principle of minimum energy dissipation and its general procedures to establish development equation of internal variable. With the accepted viewpoint that the damage is only mechanics of energy dissipation during the rockburst and utilizing the total strength criterion based on released strain energy, the general damage evolution equation is deduced. Compared with the traditional research method of damage evolution equation, this method has universal and objective characteristics.
Authors: Zheng Hua Qian, Feng Jin, Kikuo Kishimoto
Abstract: The propagation behavior of Love waves in a functionally graded material layered half-space with initial stress is taken into account. The Wentzel-Kramers-Brillouin (WKB) asymptotic technique is adopted for the theoretical derivations. The analytical solutions are obtained for the dispersion relations and the distributions of mechanical displacement and stress along thickness direction in the layered structure. Firstly, these solutions are used to study effects of the initial stress on the dispersion relations and phase velocities, then influences of the initial stress on the distributions of mechanical displacement and shear stresses along thickness direction are discussed in detail. Numerical results obtained indicate that the phase velocity of Love wave increases with the increase of the magnitude of the initial tensile stress, while decreases with the increase of the magnitude of the initial compression stress. The effects on the dispersion relations of the Love wave propagation are negligible as the magnitudes of the initial stress are less than 100MPa. Some other results are shown for distributions of field quantities along thickness direction. The results obtained are not only meaningful for the design of functionally graded structures with high performance but also effective for the evaluation of residual stress distribution in the layered structures.
Authors: Hui Min Xie, Satoshi Kishimoto, Yan Jie Li, Dao Zhi Liu, Ming Zhang, Zhen Xing Hu
Abstract: In this paper, scanning electron moiré method is used to measure the mechanical behavior of Ferro-based shape memory alloys(SMA). The moiré patterns are formed by the interference between a 1000 lines/mm cross-type specimen grating (which is fabricated using electron beam lithography) and the scanning lines of Scanning Electron Microscope (SEM). When the specimen is subjected to uniform tension load at the room temperature, the unloading residual strain values in the different regions under the same tensile load and the values in the same region under different tensile loads are compared respectively. The shape memory effect is also studied. From the experimental results, it can be concluded that the proposed moiré method is highly accurate to measure the mechanical behavior of microscopic field.

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