A Nonlinear Thermomechanical Model of Spinel Ceramics Applied to Aluminum Oxynitride (AlON)

2010 ◽  
Vol 78 (1) ◽  
Author(s):  
J. D. Clayton
Keyword(s):  
High Pressures ◽  
Shear Fracture ◽  
Experimental Investigations ◽  
Shear Stresses ◽  
Aluminum Oxynitride ◽  
Pore Collapse ◽  
Thermomechanical Model ◽  
Deformation And Failure ◽  
Dislocation Glide ◽  
Twinning Shear

A continuum model is developed for describing deformation and failure mechanisms in crystalline solids (ceramics and minerals) with the cubic spinel structure. The constitutive model describes the response under conditions pertinent to impact loading: high pressures, high strain rates, and, possibly, high temperatures. Nonlinear elasticity, anisotropy, thermoelastic coupling, dislocation glide, twinning, shear-induced fracture, and pressure-induced pore collapse are addressed. The model is applied to enable an improved understanding of transparent ceramic aluminum oxynitride (AlON). Calculations demonstrate an accurate depiction of hydrostatic and shear stresses observed experimentally in shock-loaded polycrystalline AlON. Various choices of initial resistances to slip, twinning, or shear fracture that result in similar predictions for average stresses in polycrystals but different predictions for defect densities (accumulated dislocations and twin volume fractions) are investigated. Predictions for single crystals provide insight into grain orientation effects not available from previous experimental investigations.

scholarly journals Numerical and Experimental Investigations of the Interactions between Hydraulic and Natural Fractures in Shale Formations

Energies ◽  
2018 ◽  
Vol 11 (10) ◽  
pp. 2541 ◽  
Author(s):  
Xin Chang ◽  
Yintong Guo ◽  
Jun Zhou ◽  
Xuehang Song ◽  
Chunhe Yang
Keyword(s):  
Hydraulic Fracture ◽  
Interaction Mechanism ◽  
Stress Transfer ◽  
Displacement Discontinuity ◽  
Tensile Fracture ◽  
Experimental Investigations ◽  
Shear Stresses ◽  
Natural Fractures ◽  
Stick Slip ◽  
Joint Element

Natural fractures (NFs) have been recognized as the dominant factors that increase hydraulic fracture complexity and reservoir productivity. However, the interactions between hydraulic and natural fractures are far from being fully understood. In this study, a two-dimensional numerical model based on the displacement discontinuity method (DDM) has been developed and used to investigate the interaction between hydraulic and pre-existing natural fractures. The inelastic deformation, e.g., stick, slip and separation, of the geologic discontinuities is captured by a special friction joint element called Mohr-Coulomb joint element. The dynamic stress transfer mechanisms between the two fracture systems and the possible location of secondary tensile fracture that reinitiates along the opposite sides of the NF are discussed. Furthermore, the model results are validated by a series of large tri-axial hydraulic fracture (HF) tests. Both experimental and numerical results showed that the displacements and stresses along the NFs are all in highly dynamic changes. When the HF is approaching the NF, the HF tip can exert remote compressional and shear stresses on the NF interface, which results in the debonding of the NF. The location and value of the evoked stress is a function of the far-field horizontal differential stress, inclination angle of the NF, and the net pressure used in fracturing. For a small approaching angle, the stress peak is located farther away from the intersection point, so an offset fracture is more likely to be generated. The cemented strength of the NF also has an important influence on the interaction mechanism. Weakly bonded NF surfaces increase the occurrence of a shear slippage, but for a moderate strength NF, the hybrid failure model with both tensile and shear failures, and conversion may appear.

scholarly journals Nanoindentation characterization of deformation and failure of aluminum oxynitride

2011 ◽  
Vol 59 (4) ◽  
pp. 1671-1679 ◽  
Author(s):  
J.J. Guo ◽  
K. Wang ◽  
T. Fujita ◽  
J.W. McCauley ◽  
J.P. Singh ◽  
...  
Keyword(s):  
Aluminum Oxynitride ◽  
Deformation And Failure

Mechanics of the Segmentation of an Embedded Fiber, Part I: Experimental Investigations

1995 ◽  
Vol 62 (1) ◽  
pp. 87-97 ◽  
Author(s):  
A. ten Busschen ◽  
A. P. S. Selvadurai
Keyword(s):  
Structural Parameters ◽  
Matrix Material ◽  
Micromechanical Modeling ◽  
Experimental Investigations ◽  
Shear Stresses ◽  
Research Attention ◽  
Fragmentation Test ◽  
The Matrix ◽  
Matrix Region ◽  
Interface Bond

Micromechanical modeling is an important aspect in the study of fiber-reinforced composites. In such studies, an important class of structural parameters is formed by the interaction between the matrix and the embedded fibers. These interactive processes can be investigated by an appeal to a test which involves the segmentation of an embedded fiber. This test is referred to as a “fragmentation test.” During a fragmentation test, two distinct fracture phenomena are observed. These phenomena are directly related to the integrity of bond between the embedded fiber and the matrix. The first phenomenon involves situations where the interface bond is weaker than the matrix material. In this case the fiber fragment ends will slip and in this region shear stresses are transmitted by friction and/or interlocking mechanical actions. In contrast, when the interface bond has stronger properties than the matrix material, cracking will occur in the matrix region. Here, a crack initiated in the fiber will propagate into the matrix region typically forming conoidal cracks, or combinations of conoidal and flat cracks. This paper describes the background of the fragmentation test and the associated experimental research. Attention is focused on the experimental evaluation of matrix fracture topographies encountered in the fragmentation test.

scholarly journals Clinopyroxene Solid Solutions in the CaMgSi2O6 – Ca0,5AlSi2O6 Cross-Section at High P-T Parameters

2020 ◽  
Vol 34 ◽  
pp. 37-54
Author(s):  
S. V. Banushkina ◽  
◽  
A. I. Turkin ◽  
A. I. Chepurov ◽  
◽  
...  
Keyword(s):  
Cross Section ◽  
Solid Solutions ◽  
Atmospheric Pressure ◽  
High Pressures ◽  
Experimental Investigations ◽  
Electric Resistance ◽  
Resistance Furnace ◽  
Mineral Association ◽  
Electric Resistance Furnace ◽  
Piston Cylinder

Clinopyroxenes (Cpx) are one of the main rock-forming minerals, but stoichiometry of their compositions was called into question. In particular, an idea of hypothetical calcium molecule Eskola (CaEs, Ca0,5AlSi2O6) existence was expressed. This minal has structure vacancy and silica excess. Numerous experimental investigations in CMAS-system (CaO-MgO-Al2O3-SiO2) have showed that the question of non-stoichiometric Cpx existence remains open. This paper presents the results of an experimental study of the diopside Di (CaMgSi2O6) – calcium molecule Eskola CaEs (Ca0,5AlSi2O6) cross-section in the CMAS-system. The experiments were carried out in the following pressure and temperature range: P=10-4 – 3,0 GPa; T=966 – 15250C. Experiments at atmospheric pressure (10-4 GPa) were performed on a vertical shaft electric resistance furnace; high-pressure ones were performed on a "piston-cylinder" type apparatus. Samples obtained were analyzed using electron microprobe (EMP), scanning electron microscope (SEM) and Raman spectrometer. Depending on the P-T conditions, the samples contain the following phases: anorthite An, garnet Grt, diopside Di, clinopyroxene Cpx, quartz Qtz (tridymite Tr – for experiments at atmospheric pressure), and glass L. The data array on the composition of clinopyroxenes crystallized in this cross-section with diopside in various associations is generalized and supplemented. Clinopyroxenes were found to form quaternary solid solutions of diopside Di (CaMgSi2O6) – enstatite En (Mg2Si2O6) – calcium molecule Tschermak CaTs (CaAl2SiO6) – calcium molecule Eskola CaEs (Ca0,5AlSi2O6). The CaTs and CaEs minals contents are positively correlated with the amount of aluminum in clinopyroxene, and this relationship is particularly pronounced for CaTs. It is confirmed that clinopyroxenes in this cross-section can contain an excess of silica at both atmospheric and high pressures. Apparently, the cation vacancy that exists in pyroxene structure can participate in ordering processes. As a result the pyroxenes of another structure (not diopside – C2/c-symmetry) can be crystallized from total compositions in the Di-CaEs cross-section. Additional research is needed to support this hypothesis. Besides, at present investigation it was not possible to establish an unambiguous relationship between the Cpx composition and P-T-parameters, since it is also associated with both the mixture initial composition and the mineral association. Further experiments are required to justify any geothermobarometric dependence.

scholarly journals Compression and Shear Fracture Analysis of Boundary Cracks Containing Water in Rock

2020 ◽  
Vol 2020 ◽  
pp. 1-13
Author(s):  
Zhensheng Yang ◽  
Fulin Li ◽  
Tianran Ma
Keyword(s):  
Stress Intensity ◽  
Friction Coefficient ◽  
Stress Intensity Factors ◽  
Underground Mining ◽  
Shear Fracture ◽  
Water Environment ◽  
Initial Crack ◽  
Open Boundary ◽  
Shear Stresses ◽  
Intensity Factors

In order to conserve the water resource during underground mining, the fracture and mechanical properties of rock are important for the stability of water-resisting layers, especially for the fracture behavior of boundary cracks containing water in rock. Considering the swelling of rock under water environment and the influence of water on rock, the stress intensity factors of modes I and II are derived for boundary cracks in rock under compressive and shear stresses. The cracks are divided into the closed and open states. The effects of the crack inclination angle, friction coefficient between crack surfaces, and initial crack length on stress intensity factors are also taken into account. The stress intensity factors for closed and open boundary cracks are verified by numerical and physical experiments, respectively, and the deviation of the results is within 5%. It is shown that pore pressure has different effects on the relationship between stress intensity factor and friction coefficient under different lateral pressures. The effect of water on crack propagation is mainly due to the deterioration of the fracture toughness of the rock. It is found that the critical coefficient λc is a key parameter to determine whether the boundary crack propagates in rock under compression-shear stress. Further studies should be performed to apply the present fracture theory to rock mass or water-resisting layers.

scholarly journals Evolution Rules of Fractures for Mudstone under Compression Shear Load and the Fractal Characteristics of Broken Blocks

2019 ◽  
Vol 2019 ◽  
pp. 1-7 ◽  
Author(s):  
Zhaoyun Chai ◽  
Jinbo Bai ◽  
Haiyang Zhang ◽  
Pan Yang
Keyword(s):  
Fractal Dimension ◽  
Compression Test ◽  
Shear Fracture ◽  
Fractal Theory ◽  
Friction Angle ◽  
Shear Loading ◽  
Shear Load ◽  
Deformation And Failure ◽  
Fractal Characteristics ◽  
Logarithmic Relationship

Failure of rocks is commonly induced by compressive and shear coupling loading. Knowledge of the mechanism and process of deformation and failure of rocks under compressive shear loading condition is an important basis for the study of stability in rock engineering. Based on the nonlinear fractal theory, it is possible to examine the evolution rules of fractures in mudstone under compression shear load and the fractal characteristics of broken blocks using the shear compression test with variable angles of mudstone specimens in natural conditions. This research shows that the cohesion and friction angle parameters of rock samples are achieved by draw Mohr’s strength envelope according to the test date of variable-angle shear compression test. It also shows that the shape of load-displacement curves of rocks can be divided into four stages: compaction, elastic, plastic, and fracture, and the curve can accurately represent the transformation and breakage characteristics of rock during shear fracture. And the distribution of broken blocks shows a strong statistical resemblance to the fractal distribution, and the fractal dimension is able to reflect the distribution characteristics of broken blocks. With increasing the shear angle, the fractal dimension of broken blocks decreases in a logarithmic relationship.

scholarly journals Texture analysis of experimentally deformed Black Hills Quartzite

2017 ◽  
Author(s):  
Rüdiger Kilian ◽  
Renée Heilbronner
Keyword(s):  
Black Hills ◽  
Dislocation Creep ◽  
Shear Stresses ◽  
Slip Systems ◽  
Dislocation Glide ◽  
Aspect Ratios ◽  
Deformation Intensity ◽  
Pole Figures ◽  
Three Samples ◽  
Texture Transition

Abstract. The textures of three samples of Black Hills quartzite (BHQ) deformed experimentally in the dislocation creep regime 1, 2 and 3 (according to Hirth and Tullis, 1992) have been analysed by EBSD. All samples were deformed to relatively high strain, within a temperature range of 65° and identical displacement rates and are almost entirely composed of dynamically recrystallized grains. A texture transition from peripheral c-axes in regime 1 to a central c-axis maximum in regime 3 is observed. Separate pole figures are calculated for different grain sizes, aspect ratios and long axis trend (θ) of grains, and high and low levels of intragranular deformation intensity as measured by the grain kernel average misorientation (gKAM). Misorientation relations are analysed for different texture components (named Y- B- R- and σ, with reference to previously published prism, basal, rhomb and σ1 – grains). Results show that regime 1 and 3 correspond to clear end member textures with regime 2 being transitional. Texture strength and the development of a central c-axis maximum from a girdle distribution depends on deformation intensity at the grain scale and on the contribution of dislocation creep which increases towards regime 3. Combined with calculations of resolved shear stresses and misorientation analysis, it becomes clear that the peripheral c-axis maximum in regime 1 is not due to deformation by basal –<a> slip. We interpret the texture transition as a result of different texture forming processes, one being more efficient at high stresses (formation of grains with peripheral c-axes), the other depending on strain (dislocation glide involving prism and rhomb slip systems), and not as a result of a temperature dependent activity of different slip systems.

Effects of Coriolis Force on Turbulence Structure in Rotating Channels With High and Low Aspect Ratios

2019 ◽  
Author(s):  
Hide S. Koyama ◽  
Shoichiro Tatsuta ◽  
Ema Tamura ◽  
Hani H. Nigim
Keyword(s):  
Boundary Layer ◽  
Aspect Ratio ◽  
Coriolis Force ◽  
Experimental Investigations ◽  
Shear Stresses ◽  
Turbulence Structure ◽  
Hot Wire ◽  
Aspect Ratios ◽  
Flow Effects ◽  
Vorticity Transport

Abstract To clarify the stabilization, destabilization and secondary flow effects of the Coriolis force on the turbulence structure in rotating channels with high and low aspect ratios, experimental investigations were undertaken by using a rotating wind tunnel about 2 meters in diameter. A hot-wire anemometer and more than 6 hot-wire probes with fine resistance wire, each inclined at a known angle to the main flow, were used for the measurements of time-mean velocities and 6 components of Reynolds normal and shear stresses. An optical transmission system of electrical signals from a rotating apparatus to the stationary system was used to immunize the electrical noise. The hot-wire probe was traversed with sufficient accuracy. Phenomena of the stratification, Taylor-Görtler type vortices in the destabilized nominal two-dimensional turbulent boundary layer, relaminarization from turbulent to laminar boundary layer in the high aspect ratio channel and a pair of longitudinal flat vortices in the low aspect ratio channel were observed, and discussed in detail by using the low of conservation of angular momentum, the vorticity transport equation and the Reynolds stress transport equations in a rotating frame.

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