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.

Nucleation and Boundary Layer Growth of Shear Bands in Machining

2019 ◽  
Author(s):  
Shwetabh Yadav ◽  
Dinakar Sagapuram
Keyword(s):  
Boundary Layer ◽  
Shear Band ◽  
Plastic Flow ◽  
High Speed ◽  
Cutting Speed ◽  
Critical Shear Stress ◽  
Layer Growth ◽  
Image Correlation ◽  
Material System ◽  
Band Formation

Abstract An experimental study of shear band formation in cutting of metals is made using a low melting point Bi-based alloy as a model material system. High-speed imaging is used to capture the transition in the plastic flow, from laminar to shear banded flow, as a function of cutting speed. The dynamics of shear band nucleation is captured in situ and temporal evolution of localized plastic flow during shear band growth is quantitatively analyzed using an image correlation method, particle image velocimetry (PIV). The observations show that shear band nucleation is governed by a critical shear stress criterion, and accompanied by a large drop in the flow viscosity by several orders of magnitude, analogous to the phenomenon of yielding in yield-stress (Bingham) fluids. Likewise, the displacement field around a freshly nucleated shear band evolves in a manner resembling the boundary layer formation in planar flow of a Bingham fluid with a very small viscosity. Surprisingly, temperature has little influence on shear band nucleation or growth.

scholarly journals In situ analysis of shear bands and boundary layer formation in metals

2020 ◽  
Vol 476 (2234) ◽  
pp. 20190519 ◽  
Author(s):  
Shwetabh Yadav ◽  
Dinakar Sagapuram
Keyword(s):  
Boundary Layer ◽  
Shear Band ◽  
Shear Banding ◽  
Shear Bands ◽  
Critical Shear Stress ◽  
Plastic Instability ◽  
Layer Formation ◽  
Sharp Drop ◽  
Boundary Layer Formation

Shear banding is a plastic instability in large deformation of solids where the flow becomes concentrated in narrow layers, with broad implications in materials processing applications and dynamic failure of metals. Given the extremely small length and time scales involved, several challenges persist in studying the development of shear bands. Here, we present a new approach to study shear bands at low speeds using low melting point alloys. We use in situ imaging to directly capture the essential features of shear banding, including transition from homogeneous to shear banded flow, band nucleation and propagation dynamics, and temporal evolution of the flow around a developing band. High-resolution, time-resolved measurements of the local displacement and velocity profiles during shear band growth are presented. The experiments are complemented by an analysis of the shear band growth as a Bingham fluid flow. It is shown that shear banding occurs only beyond a critical shear stress and is accompanied by a sharp drop in the viscosity by several orders of magnitude, analogous to the yielding transition in yield-stress fluids. Likewise, the displacement field around a nucleated band evolves in a manner that resembles boundary layer formation, with the band thickness scaling with time as a power law.

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.

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.

Experimental and Numerical Study of Intense Shear Banding for Al-Alloy under Uniaxial Tension

2005 ◽  
Vol 6-8 ◽  
pp. 737-744 ◽  
Author(s):  
Xin Jian Duan ◽  
Mukesh K. Jain ◽  
M. Bruhis ◽  
David S. Wilkinson
Keyword(s):  
Shear Band ◽  
Uniaxial Tension ◽  
Numerical Study ◽  
Shear Banding ◽  
Gauge Length ◽  
Image Correlation ◽  
Al Alloy ◽  
Band Formation ◽  
Full Field ◽  
Intense Shear

The occurrence of intense shear band is a prelude to failure in many Al-sheet materials. In the present study, a full field optical system measurement technique (digital image correlation) and the finite element method are used to characterize the sequence of deformation in uniaxial tension before and after the intense shear band formation in AA6111-T4. The results indicate good agreement between the measurement and the predictions in terms of shear band width, strain distribution along the gauge length and the failure mode.

Large-Scale Deformation Patterning in Geomaterials Associated with Grain Rotation

2014 ◽  
Vol 891-892 ◽  
pp. 872-877 ◽  
Author(s):  
Maxim Esin ◽  
Arcady V. Dyskin ◽  
Elena Pasternak
Keyword(s):  
Shear Band ◽  
Degrees Of Freedom ◽  
Large Scale ◽  
Shear Bands ◽  
Physical Models ◽  
Image Correlation ◽  
Deformation Pattern ◽  
Shear Band Formation ◽  
Band Formation ◽  
Subsequent Formation

Modelling of large-scale deformation patterning in geomaterials is important for predicting instabilities and failures in the Earths crust. Shear band formation and the evolution of the bands is a predominant mechanism of deformation patterning. Independent rotations of separate grains/particles can affect the pattern formation by adding the effect of rotational degrees of freedom to the mechanism of instability. To model this mechanism we use a special experimental technique based on digital image correlation in order to recover both displacement and independent rotation fields in 2D physical models of granular material. In the physical model the particles are represented by smooth steel monodispersed disks with speckles painted on them to enable the rotation reconstruction. During the loading the deformation pattern undergoes stages of shear band formation followed by its dissolution due to re-compaction and particle rearrangement with the subsequent formation of multiple shear bands merging into a single one and the final dissolution. Also, patterns of rotations are observed at an intermediate scale between the scale of the particles and the scale of the shear band.

scholarly journals Shear Bands in Materials Processing: Understanding the Mechanics of Flow Localization From Zener's Time to the Present

2020 ◽  
Vol 72 (6) ◽  
Author(s):  
Koushik Viswanathan ◽  
Shwetabh Yadav ◽  
Dinakar Sagapuram
Keyword(s):  
Shear Band ◽  
Large Strain ◽  
Shear Banding ◽  
Shear Bands ◽  
Ex Situ ◽  
Materials Processing ◽  
Complex Flow ◽  
Band Formation ◽  
Full Field ◽  
Material Systems

Abstract Shear banding is a material instability in large strain plastic deformation of solids, where otherwise homogeneous flow becomes localized in narrow micrometer-scale bands. Shear bands have broad implications for materials processing and failure under dynamic loading in a wide variety of material systems ranging from metals to rocks. This year marks 75 years since the publication of Zener and Hollomon's pioneering work on shear bands (Zener and Hollomon, J Appl. Phys., 15, 22–32, 1944), which is widely credited with drawing the attention of the mechanics community to shear bands and related localization phenomena. Since this landmark publication, there has been significant experimental and theoretical investigation into the onset of shear banding. Yet, given the extremely small length and time scales associated with band development, several challenges persist in studying the evolution of single bands, postinitiation. For instance, spatiotemporal development of strain fields in the vicinity of a band, crucial to understanding the transition from localized flow to fracture, has remained largely unexplored. Recent full-field displacement measurements, coupled with numerical modeling, have only begun to ameliorate this problem. This article summarizes our present understanding of plastic flow dynamics around single shear bands and the subsequent transition to fracture, with special emphasis on the postinstability stage. These topics are covered specifically from a materials processing perspective. We begin with a semihistorical look at some of Zener's early ideas on shear bands and discuss recent advances in experimental methods for mapping localized flow during band formation, including direct in situ imaging as well as ex situ/postmortem analyses. Classical theories and analytical frameworks are revisited in the light of recently published experimental data. We show that shear bands exhibit a wealth of complex flow characteristics that bear striking resemblance to viscous fluid flows and related boundary layer phenomena. Finally, new material systems and strategies for reproducing shear band formation at low speeds are discussed. It is hoped that these will help further our understanding of shear band dynamics, the subsequent transition to fracture, and lead to practical “control” strategies for suppressing shear band-driven failures in processing applications.

δ’ (Al3Li) dissolution as a thermal probe in shear-banding studies

1993 ◽  
Vol 51 ◽  
pp. 1178-1179
Author(s):  
Roa Wen Chen ◽  
Kenneth S. Vecchio
Keyword(s):  
Shear Band ◽  
Thermal History ◽  
Shear Banding ◽  
Shear Bands ◽  
Dissolution Kinetics ◽  
Alloy System ◽  
Thermal Probe ◽  
Band Formation ◽  
Thermal Dissolution ◽  
History Of

The Al-Li alloy system can provide a unique opportunity to study the thermal history of shear-band formation by following the thermal dissolution of the precipitate phase δ’ (Al3Li) as a function of Li concentration and δ’ solvus temperature. The Al-Li system was chosen primarily for the rather rapid precipitation and dissolution kinetics resulting from the high diffusivity of Li in the Al lattice. δ’ is a spherical, coherent and metastable precipitate which is the main strengthening phase in dilute Al-Li alloys. Although δ’ is metastable, the location of the δ’ solvus in the Al-Li phase diagram has been well documented for dilute Li additions (<5 wt.% Li).e.g.1 The metastable δ’ solvus increases in temperature with increasing Li concentration. As such, the dissolution of δ’ within the shear bands, as a function of Li alloy concentration, can provide an internal temperature probe to study the thermal history of the shear band.

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.

The Effect of Cold Rolling Reduction on Shear Band and Texture Formation in Fe-3%Si Alloy

2012 ◽  
Vol 715-716 ◽  
pp. 158-163 ◽  
Author(s):  
Kenichi Murakami ◽  
N. Morishige ◽  
Kohsaku Ushioda
Keyword(s):  
Shear Band ◽  
Cold Rolling ◽  
Crystal Orientation ◽  
Shear Bands ◽  
Rolling Direction ◽  
Orientation Distribution ◽  
Rolling Reduction ◽  
Shear Band Formation ◽  
Band Formation ◽  
Cold Rolling Reduction

The effect of cold rolling reduction on shear band formation and crystal orientation within shear bands and annealing texture were investigated in Fe-3%Si {111}<112> single crystals. Several types of shear bands were observed with different angles to rolling direction, dependent on rolling reduction. As for shear band formation, those with smaller angles were formed earlier and those with larger angles were formed later. Regarding crystal orientation along shear bands after rolling reduction, orientation distribution from the initial became large in accordance with reduction and even exceeded Goss orientation when rolling reduction became larger than 40%. After annealing, however, recrystallized grains along shear bands were mainly Goss grains regardless of reduction. The speculated reason for the dominance of Goss after annealing is that Goss subgrains with less density of dislocations were surrounded by largely deformed areas.

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