The stress field and rupture feature in compound model containing typical cracks system and hard-inclusion
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Aiming at the research on mechanical mechanism of hard-inclusion earthquake preparation model, in this paper,experimental and contrast research on stress field and rupture feature of hard-inclusion model has been made respectively, which contained en echelon and composite cracks systems in models, and was loaded under uniaxial compressive stress. The result shows that reverse en echelon and T-shape cracks systems in hard-inclusion are the favorable geological structures to trigger earthquakes.Keywords:
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Stress field
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A weakest link theory for macroscopically homogeneous isotropic materials containing randomly oriented microcracks uniformly distributed in location is developed under the assumption that fracture depends only on the macroscopic stress normal to a crack plane. The function representing the number of cracks per unit volume failing at each value of normal stress is expanded as a Taylor series with coefficients determined from tensile test data. This function is used without additional assumptions to determine the probability of fracture under arbitrary (but not predominantly compressive) stress conditions. The results can be readily incorporated into a finite-element code to predict the failure probability of any structure to which the code applies.
Brittleness
Plane stress
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Compressive fracture in rock is simulated and analyzed in terms of crack patterns and crack strain energy. Results indicate that initially cracks are randomly located and non-interesting. When {approximately}10% of the sites are cracked, crack interaction becomes important and cluster of cracked sites form and extend. Finally, a few critical connecting cracks form and link the clusters to cause failure.
Strain energy
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Residual strength
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This paper focuses on the cracking and fragmentation process in rock materials containing a pair of non-parallel flaws, which are through the specimen thickness, under vertical compression. Several numerical experiments are conducted with varying flaw arrangements that affect the initiation and tensile wing cracks, shear crack growth, and crack coalescing behaviors. To obtain realistic numerical results, a parallelized peridynamics formulation coupled with a finite element method, which is able to capture arbitrarily occurring cracks, is employed. From previous studies, crack initiation and propagation of tensile wing cracks, horsetail cracks, and anti-wing cracks are well understood along with the coalescence between two parallel flaws. In this study, the coalescence behaviors, their fragmentation sequences, and the role of an x-shaped shear band in rock material containing two non-parallel flaws are discussed in detail on the basis of simulation results strongly correlated with previous experimental results. Firstly, crack initiation and propagation of tensile wing cracks and shear cracks between non-parallel flaws are investigated in time-history and then sequential coalescing behavior is analyzed. Secondly, under the effect of varying inclination angles of two non-parallel flaws and overlapping ratios between a pair of non-parallel flaws, the cracking patterns including crack coalescence, fragmentation, and x-shaped shear band are investigated. These numerical results, which are in good agreement with reported physical test results, are expected to provide insightful information of the fracture mechanism of rock with non-parallel flaws.
Coalescence (physics)
Fragmentation
Peridynamics
Shear band
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The reliability of brittle materials under a generalized state of stress is analyzed using the Batdorf model. The model is modified to include the reduction in shear due to the effect of the compressive stress on the microscopic crack faces. The combined effect of both surface and volume flaws is included. Due to the nature of fracture of brittle materials under compressive loading, the component is modeled as a series system in order to establish bounds on the probability of failure. A computer program was written to determine the probability of failure employing data from a finite element analysis. The analysis showed that for tensile loading a single crack will be the cause of total failure but under compressive loading a series of microscopic cracks must join together to form a dominant crack.
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In many cases the lifetime of technical structures and components is depending on the behaviour of cracks. Due to the complex geometry and loading situation in real-world structures cracks are often subjected to a superposition of normal, in-plane and out-of-plane loading. Therefore, in order to construct reliable structures, it is necessary to have criteria for predicting the beginning of stable and unstable crack growth as well as the crack growth direction. In this paper, different criteria for 3D crack growth under multiaxial loading, that means superposition of the fracture modes Mode I, II and III, are described and the results are compared. New approximation functions for the description of the three-dimensional crack deflection are proposed. Die Lebensdauer von technischen Strukturen ist in vielen Fällen von dem Verhalten von Rissen abhängig. Infolge komplexer Geometrie oder komplexer Belastung sind Risse in realen Strukturen häufig durch die Überlagerung von Normal-, ebener und nichtebener Belastung beansprucht. Um Strukturen sicher auslegen zu können, ist es erforderlich, Kriterien zur Vorhersage des Beginns stabiler und instabiler Rissausbreitung und zur Vorhersage der Risswachstumsrichtung zu besitzen. In diesem Artikel werden verschiedene Kriterien für das 3D-Risswachstum unter mehrachsiger Belastung, d.h. für die Überlagerung der Rissmoden I, II und III beschrieben und ihre Ergebnisse miteinander verglichen. Neue Näherungsbeziehungen zur Beschreibung dreidimensionalen Risswachstums werden vorgeschlagen.
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Coalescence (physics)
Peridynamics
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Acoustic Emission
Micromechanics
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A team of specimens containing two parallel three-dimensional(3D) cracks are made of a newly developed resin,which is completely transparent and has more brittle fracture properties of rock-like material(tension-compression ratio is 1/6.6) than before at room temperature.The propagation and coalescence process of the cracks under uniaxial loading is described and analyzed in detail;and then its produce condition and mechanism are studied.The testing results show that the failure process of specimens can be divided into four stages.The fracture of 3D cracks,which produces many different forms of cracks,is much more complex than that of 2D cracks.Subsequently,the specimen is chosen to carry out the numerical simulation.By employing FLAC3D,the propagation process of the 3D cracks are simulated and studied by establishing a new elasto-brittle constitutive relation and using superfine and reasonable form of unit division.The numerical simulation results match well with the testing results in this paper and that obtained by former scholars,so as to show the effectiveness of the new numerical simulation method.Moreover,the simulation results also have a good consistency with the testing results obtained by former scholars under biaxial loading.
Coalescence (physics)
Brittleness
Brittle fracture
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Interaction effect of multiple flaws on ductile fracture is studied numerically by Gurson's constitutive equation. Based on experiments, 2 parallel cracks problems and 3 parallel cracks problems are simulated. In some problems, crack coalescence does not occur, and it occurs in other cases. In all cases, ductile fracture processes are obtained, and results are compared with experimental ones. Fracture pattern and load-displacement curves agree well with experiments. It is shown that void growth term is dominant for the coalescence of cracks. Slanted crack problem and non-uniform length crack problem are simulated and evaluation method of multiple cracks problem is discussed.
Coalescence (physics)
Void (composites)
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