scholarly journals Experiments on Rocks Under High Pressure Conditions in GTA 20-32 Triaxial Press / Experimenty Na Horninách Ve Vysokotlakém Triaxiálním Lisu GTA 20-32

2012 ◽  
Vol 58 (1) ◽  
pp. 9-16
Author(s):  
Josef Poláček ◽  
Alena Kožušníková
Keyword(s):  
Plastic Deformation ◽  
High Pressure ◽  
Brittle Failure ◽  
Axial Stress ◽  
Deformation Behaviour ◽  
Confining Pressure ◽  
Strength Properties ◽  
Experimental Results ◽  
State Of Stress ◽  
Different Types

Abstract The paper describes the methodology of measurements in the GTA 20-32 triaxial press. The deformation behaviour of two different types of rocks was compared: - gypsum with plastic deformation even at lower confining pressure, - Carboniferous sandstone with brittle failure even at the highest confining pressure. The influence of gypsum layering was studied as well. The experimental results show that the deformation and strength properties of the gypsum in the triaxial state of stress do not significantly depend on the orientation of axial stress to the observed layering.

scholarly journals Intragranular deformation mechanisms in calcite deformed by high-pressure torsion at room temperature

2020 ◽  
Vol 114 (2) ◽  
pp. 105-118
Author(s):  
Roman Schuster ◽  
Gerlinde Habler ◽  
Erhard Schafler ◽  
Rainer Abart
Keyword(s):  
High Pressure ◽  
Twin Boundary ◽  
Brittle Failure ◽  
Room Temperature ◽  
High Pressure Torsion ◽  
Confining Pressure ◽  
Temperature Deformation ◽  
Orientation Relationships ◽  
High Confining Pressure ◽  
Confining Pressures

AbstractPolycrystalline calcite was deformed to high strain at room-temperature and confining pressures of 1–4 GPa using high-pressure torsion. The high confining pressure suppresses brittle failure and allows for shear strains >100. The post-deformation microstructures show inter- and intragranular cataclastic deformation and a high density of mechanical e$$ \left\{01\overline{1}8\right\} $$011¯8 twins and deformation lamellae in highly strained porphyroclasts. The morphologies of the twins resemble twin morphologies that are typically associated with substantially higher deformation temperatures. Porphyroclasts oriented unfavorably for twinning frequently exhibit two types of deformation lamellae with characteristic crystallographic orientation relationships associated with calcite twins. The misorientation of the first deformation lamella type with respect to the host corresponds to the combination of one r$$ \left\{10\overline{1}4\right\} $$101¯4 twin operation and one specific f$$ \left\{01\overline{1}2\right\} $$011¯2 or e$$ \left\{01\overline{1}8\right\} $$011¯8 twin operation. Boundary sections of this lamella type often split into two separated segments, where one segment corresponds to an incoherent r$$ \left\{10\overline{1}4\right\} $$101¯4 twin boundary and the other to an f$$ \left\{01\overline{1}2\right\} $$011¯2 or e$$ \left\{01\overline{1}8\right\} $$011¯8 twin boundary. The misorientation of the second type of deformation lamellae corresponds to the combination of specific r$$ \left\{10\overline{1}4\right\} $$101¯4 and f$$ \left\{01\overline{1}2\right\} $$011¯2 twin operations. The boundary segments of this lamella type may also split into the constituent twin boundaries. Our results show that brittle failure can effectively be suppressed during room-temperature deformation of calcite to high strains if confining pressures in the GPa range are applied. At these conditions, the combination of successive twin operations produces hitherto unknown deformation lamellae.

Permeability Changes of Coal Cores and Briquettes under Tri-Axial Stress Conditions

2014 ◽  
Vol 59 (4) ◽  
pp. 1131-1140
Author(s):  
Mirosław Wierzbicki ◽  
Pavel Konečný ◽  
Alena Kožušníková
Keyword(s):  
Gas Permeability ◽  
Coal Dust ◽  
Axial Stress ◽  
Empirical Relation ◽  
Confining Pressure ◽  
Good Correspondence ◽  
State Of Stress ◽  
Good Repeatability ◽  
Axial State ◽  
Methane Capacity

Abstract The paper is dealing with the permeability of coal in triaxial state of stress. The permeability of coal, besides coal’s methane capacity, is the main parameter determining the quantity of methane inflow into underground excavations. The stress in a coal seam is one of the most important factors influencing coal permeability therefore the permeability measurements were performed in tri-axial state of stress. The hydrostatic three-axial state of stress was gradually increased from 5 MPa with steps of 5 MPa up to a maximum of 30 MPa. Nitrogen was applied as a gas medium in all experiments. The results of the permeability measurements of coal cores from the “Zofiówka” mine, Poland, and three mines from the Czech Republic are presented in this paper. As a “reference”, permeability measurements were also taken for coal briquettes prepared from coal dust with defined porosity. It was confirmed that the decreasing porosity of coal briquettes affects the decreasing permeability. The advantage of experimentation on coal briquettes is its good repeatability. From the experimental results, an empirical relation between gas permeability and confining pressure has also been identified. The empirical relation for coal briquettes is in good correspondence with published results. However, for coal cores, the character of change differs. The influence of confining pressure has a different character and the decrease in permeability is stronger due to the increasing confining pressure

Comparison between FEM and Experimental Results in the Upsetting of Nano-Structured Materials

2012 ◽  
Vol 713 ◽  
pp. 31-36 ◽  
Author(s):  
C.J. Luis-Pérez ◽  
Ignacio Puertas ◽  
Daniel Salcedo ◽  
Javier León ◽  
Ivan Pérez
Keyword(s):  
Plastic Deformation ◽  
Grain Size ◽  
High Pressure ◽  
Severe Plastic Deformation ◽  
Equal Channel Angular Extrusion ◽  
High Pressure Torsion ◽  
Experimental Results ◽  
Structured Materials ◽  
Angular Extrusion ◽  
Deformation Processes

Over recent years, some severe plastic deformation processes have been developed with the aim of obtaining a material with sub-micrometric or even nanometric grain size, such as: ECAE (Equal channel angular extrusion) and HPT (High pressure torsion) among many others. The main aim of this present study is to analyse the upsetting of the 5083 Al-Mg-Mn alloy, which had been previously deformed by ECAE. Different processing temperatures will be used and the final properties of the resulting material will be determined.

Plastic Deformation and Fracture Initiation Typology Analysis under a Triaxial Tensile State of Stress Using the Quantitative Assessment of Microstructural Changes

2012 ◽  
Vol 267 ◽  
pp. 17-24
Author(s):  
Voicu Ioan Safta ◽  
Voicu Ionel Safta
Keyword(s):  
Plastic Deformation ◽  
Axial Stress ◽  
Fracture Initiation ◽  
Deformation Degree ◽  
Stress Concentrators ◽  
State Of Stress ◽  
Deformation And Fracture ◽  
Specimen Axis ◽  
Geometric Changes ◽  
Typology Analysis

The paper approaches the influence problems, due to increase in plastic deformation and fracture initiation, upon the multi-axial stress state. The experiments are based on determining the geometric changes of stress concentrators and the increase of granulation anisotropy of unalloyed steel related to the plastic deformation. In order to evince the changes in the concentrators shape, at high levels of deformation, an average parameter of shape was introduced. The 3D Complex representations, based on measurements have indicated the dependence of longitudinal specific deformations for the deformation degree, as well as sectional position in the area under measurement. The variation functions of the longitudinal specific deformation of the medium average shape parameter showed an opposed linear dependence at the top of the tension concentrator relatively to the tested specimen axis. Taking into consideration the average parameter of shape, the experimental correlations were more conclusive. Evaluating the microstructural state of stress concentrators, the deformations have revealed distinct fracture typologies, influenced by the specific state of deformation. By synthesizing the information regarding the fracture initiation, an typological diagram of fracture initiation TDI was elaborated. In this diagram, representing the cross section of the specimens, for different values of the stress concentrator factor, six quasi-quantitative zones have been analyzed.

scholarly journals Effect of Strain Heterogeneities on Microstructure, Texture, Hardness, and H-Activation of High-Pressure Torsion Mg Consolidated from Different Powders

Materials ◽  
2018 ◽  
Vol 11 (8) ◽  
pp. 1335 ◽  
Author(s):  
Subrata Panda ◽  
Laszlo Toth ◽  
Jianxin Zou ◽  
Thierry Grosdidier
Keyword(s):  
Plastic Deformation ◽  
High Pressure ◽  
High Pressure Torsion ◽  
Local Strain ◽  
Powder Materials ◽  
Deformation Characteristics ◽  
Hydrogen Activation ◽  
Activation Kinetics ◽  
Different Types ◽  
Powder Particles

Severe plastic deformation techniques, such as high-pressure torsion (HPT), have been increasingly applied on powder materials to consolidate bulk nanostructured materials. In this context, the aim of the present study is to compare the plastic deformation characteristics during HPT of two distinct Mg-based powder precursors: (i) atomized micro-sized powder and (ii) condensed and passivated nanopowder. Dynamic recrystallization could take place during HPT consolidation of the atomized powder particles while the oxide pinning of the grain boundaries restricted it for the condensed powder. Consequently, there have been substantial differences in the development of the microstructure, texture, local strain heterogeneities, and hardness in the two types of consolidated products. Different types of local strain heterogeneities were also revealed in the consolidated products. The associated diversity in microstructure within the same consolidated product has been demonstrated to have an effect on the hydrogen activation kinetics to form hydrides for these Mg-based materials that could be suitable for solid state H-storage applications.

scholarly journals Influence of Unloading Conditions of Confining Pressure on the Compressive Strength and Permeability of Deep Mudstone

2021 ◽  
Vol 2021 ◽  
pp. 1-10
Author(s):  
Tianyu Xin ◽  
Yashengnan Sun ◽  
Junguang Wang ◽  
Weiji Sun
Keyword(s):  
Compressive Strength ◽  
Brittle Failure ◽  
Axial Stress ◽  
Triaxial Compression ◽  
Volumetric Strain ◽  
Ductile Failure ◽  
Confining Pressure ◽  
Initial Stage ◽  
Strain Change ◽  
Deep Rock

To investigate the compressive strength and permeability of deep mudstone under stress disturbance, a triaxial rheometer is used to conduct seepage experiments on mudstone specimens with different buried depths under triaxial compression and unloading conditions. The experimental results show that the compressive strength of mudstone specimen with a depth of 1000 m is much lower than that of specimen with a depth of 200 m, and the compressive strength of mudstone increases with the increase in confining pressure. Under constant axial pressure and unloading of the confining pressure, the mudstone with a depth of 200 m exhibits brittle failure, and the strain fluctuates in a pointwise manner with the increase in axial stress. In this case, the mudstone with a depth of 1000 m exhibits a transition from brittle failure to ductile failure, and the strain fluctuates linearly with the axial stress. Further, when the volumetric strain change reaches 0.01, it shows an oblique “Z” fluctuation. During the initial stage of unloading of confining pressure, the permeabilities of both the mudstone specimens (with depths of 200 and 1000 m) decrease gradually. As the confining pressure is unloaded, the permeability of mudstone with a depth of 1000 m increases. Until the specimen is completely destroyed, the permeability of mudstone increases rapidly. Overall, this study can serve as a useful reference for analyzing the engineering disasters associated with deep rock mass, tunnel ventilation, and gas storage.

Effect of length in rotational autofrettage of long cylinders with free ends

2021 ◽  
pp. 095440622110342
Author(s):  
Rajkumar Shufen ◽  
Uday Shanker Dixit
Keyword(s):  
Plastic Deformation ◽  
Residual Stresses ◽  
Axial Stress ◽  
Fem Analysis ◽  
Longitudinal Axis ◽  
Pressure Vessels ◽  
Stress Changes ◽  
Different Types ◽  
Compressive Residual Stresses ◽  
Spherical Pressure

Thick-walled cylindrical and spherical pressure vessels are often subjected to autofrettage, a process in which the vessel is loaded at the inner wall to cause a partial or complete plastic deformation emanating from the inner wall, followed by unloading. This introduces the beneficial compressive residual stresses in the vicinity of the inner wall. Depending on the type of the loading, there are five different types of autofrettage processes— hydraulic, swage, explosive, thermal and rotational. This article analyzes the rotational autofrettage, in which the cylinder to be autofrettaged is loaded by rotating it about its longitudinal axis. The centrifugal forces cause the required plastic deformation in the cylinder. Hence, when the cylinder is unloaded by bringing it to rest, compressive hoop residual stresses are introduced in the vicinity of its inner wall. When long cylinders are rotated about their axes, the distribution of axial stress changes with length of the cylinder and affects the generation of the residual stresses in the autofrettaged cylinder. This effect is investigated here by a finite element method (FEM) analysis of rotational autofrettage of cylinder made up of A723 gun steel. The FEM analysis using ABAQUS® package reveals the presence of tensile axial residual stresses in the vicinity of the inner wall of the cylinder, which increase with length. The tensile residual stresses can be mitigated by constraining the ends of the cylinder during the rotational autofrettage.

scholarly journals Dilatancy behaviour and permeability evolution of sandstone subjected to initial confining pressures and unloading rates

2021 ◽  
Vol 8 (1) ◽  
pp. 201792
Author(s):  
Honggang Zhao ◽  
Chao Liu ◽  
Gun Huang
Keyword(s):  
Mechanical Response ◽  
Axial Stress ◽  
Deformation Behaviour ◽  
Crack Density ◽  
Volumetric Strain ◽  
Confining Pressure ◽  
Permeability Evolution ◽  
Confining Pressures ◽  
Sandstone Permeability ◽  
Shear Dilatancy

Mechanical response, deformation behaviour and permeability evolution of surrounding rock under unloading conditions are of significant importance in rock engineering activities. In this research, triaxial experiments of sandstone subjected to different initial confining pressures and unloading rates under fixed axial stress were conducted. The results showed that sandstones experienced shear dilatancy before failure. However, the dilatancy factor did not decrease with increasing confining pressure, i.e. the dilatancy behaviour was not suppressed, which contradicted the phenomenon under increasing axial stress. The crack density also increased with increasing initial confining pressure. Furthermore, the normalized permeability was positively correlated with unloading rates. The sandstone permeability was closely related to the shear dilatancy behaviour. In the accelerated dilatancy stage, the relationship between normalized permeability and volumetric strain was linear at low unloading rates and nonlinear at high unloading rates. The linear/nonlinear relationship between them can directly affect the temporality of respective mutation, so as to guide the prevention of geological disasters at different excavations rates.

scholarly journals EFFECT OF VISCOSITY MODIFYING AGENTS ON DEWATERING UNDER PRESSURE AND THE PERFORMANCES OF MORTAR AND CONCRETE

2017 ◽  
Vol 7 (2) ◽  
pp. 18-29 ◽  
Author(s):  
Upendra Neupane ◽  
Parnthep Julnipitawong ◽  
Somnuk Tangtermsirikul ◽  
Akino Yusuke
Keyword(s):  
High Pressure ◽  
Flow Time ◽  
Experimental Results ◽  
Concrete Sample ◽  
Air Content ◽  
Different Types ◽  
Binder Ratio ◽  
Funnel Flow ◽  
Water To Binder Ratio

This study emphasizes the effect of viscosity modifying agents (VMAs) on bleeding and dewatering of fresh mortars under high pressure. A detailed experimental dewatering device was designed and the analysis was carried out in order to evaluate the influence of two types of VMA on dewatering of freshly mixed mortars under high pressure. Additionally, the influence of the VMAs on mortar flow and air content of concrete was investigated. Two different types of VMA, which are a surfactant type and a starch ether type with various dosages were used in the tested mortar and concrete sample having the same water to binder ratio. Experimental results showed that by using dosages of surfactant type VMA equal to or higher than 3%, the pressurized dewatering of the mortars was significantly reduced. The use of starch in mortar mixtures was ineffective to reduce dewatering of mortars under high pressure. At same water to binder ratio, the addition of surfactant type VMA slightly increased the mortar flow and the v-funnel flow time due to enhancement of the air content in mixtures whereas starch ether decreased the mortar flow and increased the v-funnel time. The results of this study indicate that the surfactant type VMA is useful to control the dewatering of concrete under high pressure.

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