scholarly journals Geometric flow control of shear bands by suppression of viscous sliding

2016 ◽  
Vol 472 (2192) ◽  
pp. 20160167 ◽  
Author(s):  
Dinakar Sagapuram ◽  
Koushik Viswanathan ◽  
Anirban Mahato ◽  
Narayan K. Sundaram ◽  
Rachid M'Saoubi ◽  
...  
Keyword(s):  
Flow Control ◽  
High Speed ◽  
Flow Instability ◽  
Shear Banding ◽  
Shear Bands ◽  
Second Phase ◽  
Geometric Flow ◽  
Localized Deformation ◽  
High Speed Imaging ◽  
Initiation Phase

Shear banding is a plastic flow instability with highly undesirable consequences for metals processing. While band characteristics have been well studied, general methods to control shear bands are presently lacking. Here, we use high-speed imaging and micro-marker analysis of flow in cutting to reveal the common fundamental mechanism underlying shear banding in metals. The flow unfolds in two distinct phases: an initiation phase followed by a viscous sliding phase in which most of the straining occurs. We show that the second sliding phase is well described by a simple model of two identical fluids being sheared across their interface. The equivalent shear band viscosity computed by fitting the model to experimental displacement profiles is very close in value to typical liquid metal viscosities. The observation of similar displacement profiles across different metals shows that specific microstructure details do not affect the second phase. This also suggests that the principal role of the initiation phase is to generate a weak interface that is susceptible to localized deformation. Importantly, by constraining the sliding phase, we demonstrate a material-agnostic method—passive geometric flow control—that effects complete band suppression in systems which otherwise fail via shear banding.

scholarly journals Symmetric shear banding and swarming vortices in bacterial superfluids

2018 ◽  
Vol 115 (28) ◽  
pp. 7212-7217 ◽  
Author(s):  
Shuo Guo ◽  
Devranjan Samanta ◽  
Yi Peng ◽  
Xinliang Xu ◽  
Xiang Cheng
Keyword(s):  
High Speed ◽  
Shear Banding ◽  
Shear Bands ◽  
Local Stress ◽  
Transport Processes ◽  
Shear Stresses ◽  
Planar Shear ◽  
Collective Motions ◽  
Swimming Bacteria ◽  
Microscopic Origin

Bacterial suspensions—a premier example of active fluids—show an unusual response to shear stresses. Instead of increasing the viscosity of the suspending fluid, the emergent collective motions of swimming bacteria can turn a suspension into a superfluid with zero apparent viscosity. Although the existence of active superfluids has been demonstrated in bulk rheological measurements, the microscopic origin and dynamics of such an exotic phase have not been experimentally probed. Here, using high-speed confocal rheometry, we study the dynamics of concentrated bacterial suspensions under simple planar shear. We find that bacterial superfluids under shear exhibit unusual symmetric shear bands, defying the conventional wisdom on shear banding of complex fluids, where the formation of steady shear bands necessarily breaks the symmetry of unsheared samples. We propose a simple hydrodynamic model based on the local stress balance and the ergodic sampling of nonequilibrium shear configurations, which quantitatively describes the observed symmetric shear-banding structure. The model also successfully predicts various interesting features of swarming vortices in stationary bacterial suspensions. Our study provides insights into the physical properties of collective swarming in active fluids and illustrates their profound influences on transport processes.

Shear band characteristics in high strain rate naval applications

2019 ◽  
Author(s):  
Michael J. P. Conway ◽  
James D. Hogan
Keyword(s):  
High Speed ◽  
Dynamic Compression ◽  
Shear Banding ◽  
Shear Bands ◽  
Critical Time ◽  
Strain Rates ◽  
Static Case ◽  
Dynamic Experiments ◽  
Naval Steels ◽  
Strain Responses

Abstract This paper explores the dynamic behavior of HSLA 65 naval steels, specifically focusing on the initiation and growth of shear bands in quasi-static and dynamic compression experiments and how these bands affect stress-strain responses. The results indicate that the yield strength for this HSLA 65 increases from 541 ± 8 MPa for quasi-static (10-3 s-1) to 1081 ± 48 MPa for dynamic rates 1853 ± 31 s-1, and the hardening exponent increases from 0.376 ± 0.028 for quasi-static to 0.396 ± 0.006 for dynamic rates. Yield behavior was found to be associated with the onset of shear banding for both strain-rates, confirmed through visualization of the specimen surface using high-speed and ultra-high-speed cameras. For the quasi-static case, shear banding and yielding was observed to occur at 2.5% strain, and were observed to grow at speeds of upwards of 38 mm/s. For the dynamic experiments, the shear banding begins at approximately 1.18 ± 0.06% strain and these can grow upwards of 2122 ± 213 m/s during post-yield softening. Altogether, these measurements are some of the first of their kind in the open literature, and provide guidance on the critical time and length scales in shear banding. This information can be used in the future to design more failure-resistant steels, which has broader applications in construction, defense, and natural resource industries.

scholarly journals Viscous Shear Banding in Cutting of Metals

2018 ◽  
Vol 140 (11) ◽  
Author(s):  
Dinakar Sagapuram ◽  
Koushik Viswanathan
Keyword(s):  
Plastic Flow ◽  
Flow Instability ◽  
Liquid Metals ◽  
Shear Banding ◽  
Shear Bands ◽  
Local Deformation ◽  
Flow Rule ◽  
Sliding Mechanism ◽  
Viscous Shear ◽  
Local Shear

Shear banding is a type of plastic flow instability with often adverse implications for cutting and deformation processing of metals. Here, we study the mechanics of plastic flow evolution within single shear bands in Ti- and Ni-based alloy systems. The local shear band displacement profiles are quantitatively mapped at high resolution using a special micromarker technique. The results show that shear bands, once nucleated, evolve by a universal viscous sliding mechanism that is independent of microstructural details. The evolution of local deformation around the band is accurately captured by a momentum diffusion equation based on a Bingham-type flow rule. The predicted band viscosity is very small, compared to those of liquid metals. A plausible explanation for this small viscosity and fluid-like behavior at the band, based on phonon drag, is presented.

Stress-assisted-electrochemical corrosion of Cu-based bulk metallic glass

2010 ◽  
Vol 25 (3) ◽  
pp. 592-597 ◽  
Author(s):  
Ding Li ◽  
Mimi Yang ◽  
Fuqian Yang ◽  
Peter K. Liaw
Keyword(s):  
Metallic Glass ◽  
Bulk Metallic Glass ◽  
Current Density ◽  
Deformation Zone ◽  
Shear Banding ◽  
Shear Bands ◽  
Electrochemical Corrosion ◽  
Indentation Load ◽  
Localized Deformation ◽  
Load Range

Using the microindentation test, the stress-assisted-electrochemical corrosion of Cu46.25Zr45.25Al7.5Er1 bulk metallic glass (BMG) was studied in a 10 wt% NaCl electrolyte. The microindentation was performed in an indentation load range of 500 to 4000 mN to create shear bands over the deformation zone. Electric current of various densities was passed through the indented BMGs to evaluate the effect of shear bands and localized deformation on the electrochemical corrosion of the BMGs. Surface pits always initiated from the shear-banding zone and the contact edges between the indenter and the BMGs, and the size of the corroded zone grew with the increase in the polarization time, the indentation load, and the current density. Wormlike amorphous whiskers were formed over the corroded zone, and the density of the wormlike whiskers increased with the current density and polarization time.

Viscous Shear Banding in Cutting of Metals

2018 ◽  
Author(s):  
Dinakar Sagapuram ◽  
Koushik Viswanathan
Keyword(s):  
Plastic Flow ◽  
Flow Instability ◽  
Liquid Metals ◽  
Shear Banding ◽  
Shear Bands ◽  
Local Deformation ◽  
Bingham Flow ◽  
Sliding Mechanism ◽  
Viscous Shear ◽  
Local Shear

Shear banding is a type of plastic flow instability with often adverse implications for cutting and deformation processing of metals. Here, we study the mechanics of plastic flow evolution within single shear bands in two different (Ti and Ni-based) alloy systems. The local shear band displacement profiles are quantitatively mapped at high resolution using a special micro-marker technique. The results show that shear bands, once nucleated, evolve by a universal viscous sliding mechanism that is independent of microstructural details. The evolution of local deformation around the band is accurately captured using a simple momentum diffusion model by assuming Bingham flow rheology for the band material. The predicted band viscosity is very small, comparable to those of liquid metals. A plausible explanation for this small viscosity and fluid-like behavior at the band, based on phonon drag, is presented.

scholarly journals Nucleation properties of isolated shear bands

2020 ◽  
Vol 476 (2241) ◽  
pp. 20200529
Author(s):  
Shwetabh Yadav ◽  
Dinakar Sagapuram
Keyword(s):  
High Speed ◽  
Shear Banding ◽  
Shear Bands ◽  
Critical Shear Stress ◽  
Plastic Instability ◽  
Dislocation Slip ◽  
Flow Mode ◽  
Nucleation Kinetics ◽  
Lattice Instability ◽  
Wide Range

Shear banding, or localization of intense strains along narrow bands, is a plastic instability in solids with important implications for material failure in a wide range of materials and across length scales. In this article, we report on a series of experiments on the nucleation of single isolated shear bands in three model alloys. Nucleation kinetics of isolated bands and characteristic stresses are studied using high-speed in situ imaging and parallel force measurements. The results demonstrate the existence of a critical shear stress required for band nucleation. The nucleation stress bears little dependence on the normal stress and is proportional to the shear modulus. These properties are quite akin to those governing the onset of dislocation slip in crystalline solids. A change in the flow mode from shear banding to homogeneous plastic flow occurs at stress levels below the nucleation stress. Phase diagrams delineating the strain, strain rate and temperature domains where these two contrasting flow modes occur are presented. Our work enables interpretation of shear band nucleation as a crystal lattice instability due to (stress-assisted) breakdown of dislocation barriers, with quantitative experimental support in terms of stresses and the activation energy.

scholarly journals Torsional fracture of viscoelastic liquid bridges

2021 ◽  
Vol 118 (24) ◽  
pp. e2104790118
Author(s):  
San To Chan ◽  
Frank P. A. van Berlo ◽  
Hammad A. Faizi ◽  
Atsushi Matsumoto ◽  
Simon J. Haward ◽  
...  
Keyword(s):  
High Speed ◽  
Flow Instability ◽  
Viscoelastic Liquid ◽  
Viscoelastic Flow ◽  
Liquid Bridges ◽  
Normal Stresses ◽  
High Speed Imaging ◽  
Food Engineering ◽  
Localize Shear ◽  
Torsional Fracture

Short liquid bridges are stable under the action of surface tension. In applications like electronic packaging, food engineering, and additive manufacturing, this poses challenges to the clean and fast dispensing of viscoelastic fluids. Here, we investigate how viscoelastic liquid bridges can be destabilized by torsion. By combining high-speed imaging and numerical simulation, we show that concave surfaces of liquid bridges can localize shear, in turn localizing normal stresses and making the surface more concave. Such positive feedback creates an indent, which propagates toward the center and leads to breakup of the liquid bridge. The indent formation mechanism closely resembles edge fracture, an often undesired viscoelastic flow instability characterized by the sudden indentation of the fluid’s free surface when the fluid is subjected to shear. By applying torsion, even short, capillary stable liquid bridges can be broken in the order of 1 s. This may lead to the development of dispensing protocols that reduce substrate contamination by the satellite droplets and long capillary tails formed by capillary retraction, which is the current mainstream industrial method for destabilizing viscoelastic liquid bridges.

An Investigation into the Microstructure of Adiabatic Shear Banding in AISI 1045 Hardened Steel due to High Speed Machining

2010 ◽  
Vol 154-155 ◽  
pp. 321-324 ◽  
Author(s):  
Chun Zheng Duan ◽  
Liang Chi Zhang ◽  
Hai Yang Yu ◽  
Min Jie Wang
Keyword(s):  
High Speed ◽  
Shear Banding ◽  
Shear Bands ◽  
Adiabatic Shear ◽  
High Speed Machining ◽  
Adiabatic Shear Bands ◽  
Adiabatic Shear Banding ◽  
Aisi 1045 ◽  
Cutting Speeds ◽  
Electronic Microscope

Adiabatic shear banding during high speed machining is important to understand material removal mechanisms. This paper investigates the microstructure of adiabatic shear bands (ASBs) in the serrated chips produced during the high speed machining of AISI 1045 hardened steel. Optical microscope, scanning electronic microscope(SEM) and transmission electronic microscope(TEM) were used to explore the microstructural characteristics. It was found that there are two types of adiabatic shear bands. One is the deformed adiabatic shear band composed of a significantly deformed structure generated in a range of low cutting speeds, and the other is the transformed adiabatic shear band composed of very small equiaxed grains generated under high cutting speeds. The results indicated that the deformed band has a tempered martensite structure that formed through large plastic deformation and the transformed band has experienced a dynamic recrystallization process.

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