scholarly journals Experimental Study on the Shear Band of Methane Hydrate-Bearing Sediment

2021 ◽  
Vol 9 (11) ◽  
pp. 1158
Author(s):  
Xiaobing Lu ◽  
Xuhui Zhang ◽  
Fangfang Sun ◽  
Shuyun Wang ◽  
Lele Liu ◽  
...  
Keyword(s):  
Shear Band ◽  
Gas Hydrate ◽  
Methane Hydrate ◽  
Triaxial Compression ◽  
Shear Banding ◽  
Oblique Line ◽  
Shear Bands ◽  
Compression Tests ◽  
Computer Tomography Scan ◽  
Hydrate Saturation

The occurrence of a shear band is often thought as the precursor of failure. To study the initiation of shear banding in gas hydrate-bearing sediments, two groups of triaxial compression tests combined with a CT (computer tomography) scan were conducted by triaxial CT-integrated equipment under two confining pressures and seven hydrate saturations. The macro stress–strain curves and the corresponding CT scanning images of the micro-structure and the distribution of the components were obtained. The geometric parameters of the shear bands were measured based on the CT images at four typical axial strains, respectively. The distribution characteristics of soil particles, water, hydrate and gas were also analyzed. It is shown that the existence of methane hydrate changes the mechanical property of hydrate-bearing sediment from plastic failure to brittle failure when the hydrate saturation is over 13%, which occurs in the range of the tests in this paper. The peak of the deviatoric stress increases with the hydrate saturation. The shear band is in either a single oblique line or inter-cross lines depending on the hydrate saturation, the effective confining pressure and the initial distribution of the gas hydrate. Most of the shear band surfaces are not straight, and the widths of the shear bands are almost non-uniformly distributed.

Mobilized strength components of Athabasca oil sand in triaxial compression

1999 ◽  
Vol 36 (4) ◽  
pp. 718-735 ◽  
Author(s):  
Ron CK Wong
Keyword(s):  
Critical State ◽  
Triaxial Compression ◽  
Shear Banding ◽  
Shear Bands ◽  
Compression Tests ◽  
Oil Sand ◽  
Shear Dilation ◽  
X Ray Imaging ◽  
Microscopy Techniques ◽  
Triaxial Compression Tests

Dense uncemented Athabasca oil sand specimens exhibit unusually high peak strength, dilation with severe softening, and residual strength in drained triaxial compression tests. Computer tomography scanning, X-ray imaging, and scanning electron microscopy techniques are used to examine the microstructural features of the sheared specimens, such as interlocked structure, shear-banding pattern, and porosity distributions inside and outside shear bands. The characteristics of these microstructural features are used to explain the macrodeformation responses observed in the triaxial compression tests. Mobilization of strength components derived from interlocked structure, dilation, rolling, and critical state are analyzed for pre-peak, post-peak softening, and residual states.Key words: oil sand, interlocked structure, shear dilation, shear band, critical state.

scholarly journals A Constitutive Model for Locally Drained Shear Bands in Globally Undrained Dense Sand

2019 ◽  
Vol 92 ◽  
pp. 16005
Author(s):  
Hansini Mallikarachchi ◽  
Kenichi Soga
Keyword(s):  
Shear Band ◽  
Constitutive Model ◽  
Bifurcation Analysis ◽  
Shear Bands ◽  
Constitutive Relationship ◽  
Excess Pore Pressure ◽  
Biaxial Compression ◽  
Compression Tests ◽  
Equilibrium Equations ◽  
Dense Sand

When saturated granular materials which are dilative in nature are subjected to the undrained deformation, their strength increases due to the generation of negative excess pore pressure. This phenomenon is known as dilative hardening and can be witnessed in saturated dense sand or rocks during very fast loading. However, experimental evidence of undrained biaxial compression tests of dense sand shows a limit to this dilative hardening due to the formation of shear bands. There is no consensus in the literature about the mechanism which triggers these shear bands in the dense dilative sand under isochoric constraint. The possible theoretical reasoning is the local drainage inside the specimen under the globally undrained condition, which is challenging to be monitored experimentally. Hence, both incept of localisation and post-bifurcation of the saturated undrained dense sand demand further numerical investigation. Pathological mesh dependency hinders the ability of the finite element method to represent the localisation without advanced regularisation methods. This paper attempt to provide a macroscopic constitutive behaviour of the undrained deformation of the saturated dense sand in the presence of a locally drained shear band. Discontinuation of dilatant hardening due to partial drainage between the shear band and the adjacent material is integrated into the constitutive model without changing governing equilibrium equations. Initially, a classical bifurcation analysis is conducted to detect the inception and inclination of the shear band based on the underlying drained deformation. Then a post-bifurcation analysis is carried out assuming an embedded drained or partially drained shear band at gauss points which satisfy bifurcation criterion. The smeared shear band approach is utilised to homogenise the constitutive relationship. It is observed that the dilatant hardening in the saturated undrained dense sand is reduced considerably due to the formation of shear bands.

Hot Deformation and Dynamic Recrystallization in Titanium Aluminide

2018 ◽  
Vol 941 ◽  
pp. 1391-1396 ◽  
Author(s):  
Nitish Bibhanshu ◽  
Satyam Suwas
Keyword(s):  
Shear Band ◽  
Dynamic Recrystallization ◽  
Titanium Aluminide ◽  
Volume Fraction ◽  
Shear Bands ◽  
Hot Workability ◽  
Compression Tests ◽  
Electron Backscattered Diffraction ◽  
Gamma Titanium Aluminide ◽  
Z Contrast

The hot workability of gamma titanium aluminide alloy, Ti-48Al-2V-2Nb, was assessed in the cast condition through a series of compression tests conducted over a range of temperatures (1000 to 1175 °C) and at the strain rate of 10 S-1. The mechanism of dynamics recrystallization has been investigated from SEM Z-contrast images and from the Electron backscattered diffraction EBSD as well. It has been observed that volume fraction of the recrystallized grains increases with increasing the deformation temperature. The major volume fraction of the recrystallized grains was observed in the shear band which was forming at an angle 45 ̊ with respect to the compression direction. The mechanism of breaking of the laths and the region of the dynamic recrystallization were also investigated from the SEM Z-contrast image and EBSD. The dynamic recrystallization occurred in the region of the broken laths and shear bands. The breaking of the laths was because of the kinking of the lamellae. The shear band, kinked lamellae and dynamic recrystallized region where all investigated simultaneously.

The influence of material non-uniformity preceding shear-band formation in a model for granular flow

1997 ◽  
Vol 8 (5) ◽  
pp. 457-483 ◽  
Author(s):  
DAVID G. SCHAEFFER ◽  
MICHAEL SHEARER
Keyword(s):  
Shear Band ◽  
Material Properties ◽  
Shear Banding ◽  
Shear Bands ◽  
Small Variation ◽  
Band Formation ◽  
Time Period ◽  
Single Location ◽  
Change Of Type ◽  
Short Time

The onset of shear-banding in a deforming elastoplastic solid has been linked to change of type of the governing partial differential equations. If uniform material properties are assumed, then (i) deformations prior to shear-banding are uniform, and (ii) the onset of shear-banding occurs simultaneously at all points in the sample. In this paper we study, in the context of a model for anti-plane shearing of a granular material, the effect of a small variation in material properties (e.g. in yield strength) within the sample. Using matched asymptotic expansions, we find that (i) the deformation is extremely non-uniform in a short time period immediately preceding the formation of shear-bands; and (ii) generically, a shear-band forms at a single location in the sample.

Nucleation and Boundary Layer Growth of Shear Bands in Machining

2019 ◽  
Vol 141 (10) ◽  
Author(s):  
Shwetabh Yadav ◽  
Dinakar Sagapuram
Keyword(s):  
Boundary Layer ◽  
Shear Band ◽  
Shear Banding ◽  
Shear Bands ◽  
Critical Shear Stress ◽  
Correlation Method ◽  
Layer Growth ◽  
Image Correlation ◽  
Band Formation ◽  
Stress Criterion

We demonstrate a novel approach to study shear banding in machining at low speeds using a low melting point alloy. In situ imaging and an image correlation method, particle image velocimetry (PIV), are used to capture shear band nucleation and quantitatively analyze the temporal evolution of the localized plastic flow around a shear band. The observations show that the shear band onset is governed by a critical shear stress criterion, while the displacement field around a freshly nucleated shear band evolves in a manner resembling the classical boundary layer formation in viscous fluids. The relevant shear band parameters, the stress at band formation, and local shear band viscosity are presented.

Undrained triaxial tests on water-saturated methane hydrate-bearing clayey-silty sediments of the South China Sea

2020 ◽  
Author(s):  
Lei Wang ◽  
Yanghui Li ◽  
Shi Shen ◽  
Tao Liu ◽  
Weiguo Liu ◽  
...  
Keyword(s):  
South China Sea ◽  
South China ◽  
Gas Hydrate ◽  
Methane Hydrate ◽  
The South China Sea ◽  
The South ◽  
China Sea ◽  
Fine Grained ◽  
Hydrate Saturation ◽  
Water Saturated

Approximately 90% of gas hydrates are buried in fine-grained sediments on earth, especially in the South China Sea. The potential instability of the fine-grained sediments induced by hydrate dissociation requires us to investigate the shear strength and pore pressure response of the sediments during the hydrate recovery. To date, most of studies focused on the undrained mechanical behavior of gas hydrate-bearing sand or gas hydrate-free clay, and few studies examined gas hydrate-bearing fine-grained sediments. According to the low-permeability and water-saturated characteristics of the sediments in the South China Sea, we performed a series of undrained triaxial shear tests on water-saturated methane hydrate-bearing clayey-silty sediments in this area. The experiment results show that the failure strength of methane hydrate-bearing sediments (MHBSs) increases with the increase in hydrate saturation and initial effective mean stress. The excess pore water pressure of MHBSs remains positive during shear. The cohesion in Mohr-Coulomb model increases with the increase in hydrate saturation, while the internal friction angle in Mohr-Coulomb model has little dependence on the hydrate saturation.

Analysis of serrations and shear bands fractality in UFGs

2015 ◽  
Vol 24 (1-2) ◽  
pp. 1-9 ◽  
Author(s):  
Aggelos C. Iliopoulos ◽  
Nikolaos S. Nikolaidis ◽  
Elias C. Aifantis
Keyword(s):  
Shear Band ◽  
Shear Banding ◽  
Shear Bands ◽  
Ultrafine Grain ◽  
Strain Rates ◽  
Stress Strain ◽  
Band Formation ◽  
Serrated Flow ◽  
Multiple Shear Band ◽  
First Case

AbstractTsallis nonextensive statistics is employed to characterize serrated flow, as well as multiple shear band formation in ultrafine grain (UFG) size materials. Two such UFG materials, a bi-modal Al-Mg alloy and a Fe-Cu alloy, were chosen. In the first case, at low strain rates serrated flow emerges as recorded in the stress-strain graphs, whereas at high strain rates, extensive shear banding occurs. In the second case, multiple shear banding is the only mechanism for plastic deformation, but serrations in the stress-strain graph are not recorded. The analysis aims at the estimation of Tsallis entropic index qstat (stat denotes stationary state), as well as the estimation of fractal dimension. The results reveal that the distributions of serrations and shear bands do not follow Gaussian statistics as implied by Boltzmann-Gibbs extensive thermodynamics, but are approximated instead by Tsallis q-Gaussian distributions, as suggested by nonextensive thermodynamics. In addition, fractal analysis of multiple shear band images reveals a (multi)fractal and hierarchical profile of the spatial arrangement of shear bands.

Shear Band Feature in Two Bulk Metallic Glasses with Different Inherent Plasticity

2013 ◽  
Vol 703 ◽  
pp. 20-23
Author(s):  
Jian Sheng Gu ◽  
Hui Feng Bo ◽  
Hong Li ◽  
Zhan Xin Zhang
Keyword(s):  
Plastic Deformation ◽  
Shear Band ◽  
Temperature Rise ◽  
Metallic Glasses ◽  
Shear Banding ◽  
Shear Bands ◽  
Significant Difference ◽  
Coating Method ◽  
Deformation Ability

Shear banding characterization of Zr64.13Cu15.75Ni10.12Al10 and Zr65Cu15Ni10Al10 BMGs was studied by using Rockwell indention method. The significant difference in plastic deformation ability can be ascribed to different shear banding features. Meanwhile, by using the fusible coating method, thermal effect on shear bands was investigated. We did not see apparently temperature rise in shear bands of these two BMGs through Rockwell indentation.

In-situ TEM investigation of deformation behavior of metallic glass pillars

2009 ◽  
Vol 1185 ◽  
Author(s):  
Changqiang Chen ◽  
Yutao Pei ◽  
Jeff De Hosson
Keyword(s):  
Metallic Glass ◽  
Focused Ion Beam ◽  
Axial Stress ◽  
Ion Beam ◽  
Shear Banding ◽  
Shear Bands ◽  
Deformation Mode ◽  
In Situ Tem ◽  
Compression Tests

AbstractWe show results of in situ TEM (Transmission electron microscope) quantitative investigations on the compression behaviors of amorphous micropillars fabricated by focused ion beam from Cu47Ti33Zr11Ni6Sn2Si1 metallic glass (MG) ribbon. Pillars with well defined gauge sections and tip diameter ranging from 100 nm to 640 nm are studied. Quantitative compression tests were performed by a recently developed Picoindenter TEM holder, with the evolution of individual shear bands monitored in real time in TEM. It is found that the deformation of the MG pillars at the present size domain is still dominated by discrete shear banding as demonstrated by intermittent events in the load-displacement curves. However, the frequency, amplitude and distribution of these shear banding events are clearly size dependent at submicrometer scale, leading to an apparently transition in deformation mode from highly localized inhomogeneous deformation to less localized and more distributed deformation with decreasing pillars diameter. Deformation of a 105 nm diameter pillar having rounded tips is characterized with fully homogeneous bulge at the initial stage of deformation, indicating prompting effect of multi-axial stress state on transition to fully homogeneous deformation.

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