scholarly journals Shear-banding in entangled xanthan solutions: tunable transition from sharp to broad shear-band interfaces

Soft Matter ◽  
2018 ◽  
Vol 14 (5) ◽  
pp. 826-836 ◽  
Author(s):  
H. Tang ◽  
T. Kochetkova ◽  
H. Kriegs ◽  
J. K. G. Dhont ◽  
M. P. Lettinga
Keyword(s):  
Shear Band ◽  
Shear Banding ◽  
Velocity Profiles ◽  
Sharp Interface ◽  
Polymer Chains ◽  
Smooth Transition ◽  
Local Interactions

The smooth transition between gradient-banded velocity profiles with a sharp interface and curved velocity profiles in entangled xanthan suggests that stiffness and local interactions between the sliding polymer chains play essential roles in shear banding in entangled polyelectrolytes.

scholarly journals Characterization of velocity fluctuations and the transition from transient to steady state shear banding with and without pre-shear in a wormlike micelle solution under shear startup by Rheo-NMR

2020 ◽  
Vol 30 (1) ◽  
pp. 1-13
Author(s):  
Rehab N. Al-kaby ◽  
Sarah L. Codd ◽  
Joseph D. Seymour ◽  
Jennifer R. Brown
Keyword(s):  
Steady State ◽  
Shear Rate ◽  
Shear Band ◽  
Shear Banding ◽  
Velocity Profiles ◽  
Concentric Cylinder ◽  
Stress Plateau ◽  
Interface Position ◽  
Shear Rates ◽  
Micelle Solution

AbstractRheo-NMR velocimetry was used to study shear banding of a 6 wt.% cetylpyridinium chloride (CPCl) worm-like micelle solution under shear startup conditions with and without pre-shear. 1D velocity profiles across the fluid gap of a concentric cylinder Couette shear cell were measured every 1 s following shear startup for four different applied shear rates within the stress plateau. Fitting of the velocity profiles allowed calculation of the shear banding characteristics (shear rates in the high and low shear band, the interface position and apparent slip at the inner rotating wall) as the flow transitioned from transient to steady state regimes. Characteristic timescales to reach steady state were obtained and found to be similar for all shear banding characteristics. Timescales decreased with increasing applied shear rate. Large temporal fluctuations with time were also observed and Fourier transform of the time and velocity autocorrelation functions quantified the fluctuation frequencies. Frequencies corresponded to the elastically driven hydrodynamic instabilities, i.e. vortices, that are known to occur in the unstable high shear band and were dependent upon both applied shear rate and the pre-shear protocol.

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.

scholarly journals Identifying structural signatures of shear banding in model polymer nanopillars

Soft Matter ◽  
2019 ◽  
Vol 15 (22) ◽  
pp. 4548-4561 ◽  
Author(s):  
Robert J. S. Ivancic ◽  
Robert A. Riggleman
Keyword(s):  
Machine Learning ◽  
Shear Band ◽  
Defect Structure ◽  
Amorphous Materials ◽  
Shear Banding ◽  
Shear Band Formation ◽  
Learning Methods ◽  
Band Formation ◽  
Mesoscale Models ◽  
Machine Learning Methods

Shear band formation often proceeds fracture in amorphous materials. While mesoscale models postulate an underlying defect structure to explain this phenomenon, they do not detail the microscopic properties of these defects especially in strongly confined materials. Here, we use machine learning methods to uncover these microscopic defects in simulated polymer nanopillars.

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.

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.

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.

Analysis of Localized Shear Band Formation and Post Shear Banding in FCC Single Crystals

2000 ◽  
Vol 2000.1 (0) ◽  
pp. 23-24
Author(s):  
Shokichi KANNO ◽  
Koichi ITO ◽  
Jun NITTA ◽  
Yoshihiro KAMADA ◽  
Taketoshi SAGAWA
Keyword(s):  
Shear Band ◽  
Single Crystals ◽  
Shear Banding ◽  
Shear Band Formation ◽  
Band Formation

scholarly journals Dilatancy induced ductile–brittle transition of shear band in metallic glasses

2018 ◽  
Vol 474 (2212) ◽  
pp. 20170836 ◽  
Author(s):  
F. Zeng ◽  
M. Q. Jiang ◽  
L. H. Dai
Keyword(s):  
Shear Band ◽  
Metallic Glasses ◽  
Shear Failure ◽  
Scaling Law ◽  
Shear Banding ◽  
Structural Evolution ◽  
Atomic Scale ◽  
Serrated Flow ◽  
Brittle Transition ◽  
Evolution Dynamics

Dilatancy-generated structural disordering, an inherent feature of metallic glasses (MGs), has been widely accepted as the physical mechanism for the primary origin and structural evolution of shear banding, as well as the resultant shear failure. However, it remains a great challenge to determine, to what degree of dilatation, a shear banding will evolve into a runaway shear failure. In this work, using in situ acoustic emission monitoring, we probe the dilatancy evolution at the different stages of individual shear band in MGs that underwent severely plastic deformation by the controlled cutting technology. A scaling law is revealed that the dilatancy in a shear band is linearly related to its evolution degree. A transition from ductile-to-brittle shear bands is observed, where the formers dominate stable serrated flow, and the latter lead to a runaway instability (catastrophe failure) of serrated flow. To uncover the underlying mechanics, we develop a theoretical model of shear-band evolution dynamics taking into account an atomic-scale deformation process. Our theoretical results agree with the experimental observations, and demonstrate that the atomic-scale volume expansion arises from an intrinsic shear-band evolution dynamics. Importantly, the onset of the ductile–brittle transition of shear banding is controlled by a critical dilatation.

scholarly journals Modelling the Shear Banding in Gradient Nano-Grained Metals

Nanomaterials ◽  
2021 ◽  
Vol 11 (10) ◽  
pp. 2468
Author(s):  
Tianyu Chen ◽  
Jianjun Li
Keyword(s):  
Grain Size ◽  
Shear Band ◽  
Uniform Elongation ◽  
Shear Banding ◽  
Shear Bands ◽  
Applied Strain ◽  
Grain Structure ◽  
Coarse Grained ◽  
Gradient Material ◽  
Material Surface

Extensive experiments have shown that gradient nano-grained metals have outstanding synergy of strength and ductility. However, the deformation mechanisms of gradient metals are still not fully understood due to their complicated gradient microstructure. One of the difficulties is the accurate description of the deformation of the nanocrystalline surface layer of the gradient metals. Recent experiments with a closer inspection into the surface morphology of the gradient metals reported that shear bands (strain localization) occur at the surface of the materials even under a very small, applied strain, which is in contrast to previously suggested uniform deformation. Here, a dislocation density-based computational model is developed to investigate the shear band evolution in gradient Cu to overcome the above difficulty and to clarify the above debate. The Voronoi polygon is used to establish the irregular grain structure, which has a gradual increase in grain size from the material surface to the interior. It was found that the shear band occurs at a small applied strain in the surface region of the gradient structure, and multiple shear bands are gradually formed with increasing applied load. The early appearance of shear banding and the formation of abundant shear bands resulted from the constraint of the coarse-grained interior. The number of shear bands and the uniform elongation of the gradient material were positively related, both of which increased with decreasing grain size distribution index and gradient layer thickness or increasing surface grain size. The findings are in good agreement with recent experimental observations in terms of stress-strain responses and shear band evolution. We conclude that the enhanced ductility of gradient metals originated from the gradient deformation-induced stable shear band evolution during tension.

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