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.

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.

Studies of Elastic-Plastic Instabilities

1999 ◽  
Vol 66 (1) ◽  
pp. 3-9 ◽  
Author(s):  
V. Tvergaard
Keyword(s):  
Shear Band ◽  
Plastic Flow ◽  
Continuum Mechanics ◽  
Shear Band Formation ◽  
Band Formation ◽  
Elastic Plastic ◽  
Localized Necking ◽  
Focus On Results ◽  
Metal Sheets ◽  
Bifurcation Behavior

Analyses of plastic instabilities are reviewed, with focus on results in structural mechanics as well as continuum mechanics. First the basic theories for bifurcation and post-bifurcation behavior are briefly presented. Then, localization of plastic flow is discussed, including shear band formation in solids, localized necking in biaxially stretched metal sheets, and the analogous phenomenon of buckling localization in structures. Also some recent results for cavitation instabilities in elastic-plastic solids are reviewed.

Effects of Crystallographic Texture on Plastic Flow Localization

2007 ◽  
Vol 340-341 ◽  
pp. 211-216
Author(s):  
Mitsutoshi Kuroda
Keyword(s):  
Shear Band ◽  
Plane Strain ◽  
Plastic Flow ◽  
Texture Component ◽  
Three Dimensional ◽  
Cube Texture ◽  
Shear Band Formation ◽  
Flow Localization ◽  
Band Formation ◽  
Plastic Flow Localization

In this study, effects of typical texture components observed in rolled aluminum alloy sheets (i.e. Copper, Brass, S, Cube and Goss texture components) on plastic flow localization are studied. The material response is described by a generalized Taylor-type polycrystal model, in which each grain is characterized in terms of an elastic-viscoplastic continuum slip constitutive relation. First, forming limits of thin sheet set by sheet necking are predicted using a Marciniak–Kuczynski (M–K-) type approach. It is shown that only the Cube texture component yields forming limits higher than that for a random texture in the biaxial stretch range. Next, three-dimensional shear band analyses are performed, using a three-dimensional version of M–K-type model, but the overall deformation mode is restricted to a plane strain state. From this simple model analysis, two important quantities regarding shear band formation are obtained: i.e. the critical strain at the onset of shear banding and the corresponding orientation of shear band. It is concluded that the Cube texture component is said to be a shear band free texture, while some texture components exhibit significantly low resistance to shear band formation. Finally, shear band developments in plane strain pure bending of sheet specimens with the typical textures are studied.

Experimental Study of the Influence of the Pore Water Pressure Evolution and the Shear Band Formation on the Extraction Resistance of Submerged Anchor Plates

2018 ◽  
Author(s):  
Manuela Kanitz ◽  
Juergen Grabe
Keyword(s):  
Experimental Study ◽  
Shear Band ◽  
Pore Water ◽  
High Speed ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Offshore Structures ◽  
Shear Band Formation ◽  
Band Formation ◽  
Anchor Plates

Floating offshore structures used to generate wind energy are founded on submerged foundations such as anchor plates. Their extraction resistance is of major importance during and at the end of the lifetime cycle of these offshore structures. During their lifetime cycle, the foundation is suspended to complex loading conditions due to waves, tidal currents and wind loads. To guarantee a stable structure, the extraction resistance of the anchor plates has to be known. At the end of the lifetime cycle of the offshore structures, the extraction resistance is mainly influencing the removal of the anchor plates. This resistance is a lot higher than the sum of its self-weight and hydrostatic and earth pressure acting on the structure. With initiation of a motion of the anchor plate, the volume underneath this structure is increased leading to negative pore water pressure until inflowing pore water is filling the newly created volume. In order to investigate this effect, an extensive experimental study at model scale with a displacement-driven extraction is performed. Pore pressure measurements are carried out at various locations in the soil body and underneath the plate. The soil movement is tracked with a high-speed camera to investigate the shear band formation with the particle image velocimetry method (PIV). The experiments will be conducted considering different packing densities of the soil body and at different extraction velocities to investigate their effect on the extraction resistance of anchor plates.

Chip Formation Characteristics in High-Speed Machining of Hardened AISI1045 Steel

2012 ◽  
Vol 565 ◽  
pp. 484-489
Author(s):  
Bing Wang ◽  
Zhan Qiang Liu ◽  
Qi Biao Yang
Keyword(s):  
Shear Band ◽  
Chip Formation ◽  
High Speed ◽  
Adiabatic Shear Band ◽  
Cutting Speed ◽  
Adiabatic Shear ◽  
High Speed Machining ◽  
Micro Hardness ◽  
Serrated Chip ◽  
Aisi1045 Steel

Analyzing mechanism of the chip formation is a significant way to understand the metal cutting process better. The characterization of serrated chip formation in high speed machining of hardened AISI1045 steel is investigated with the aid of optical microscopy and micro-hardness measurement in this paper. The chip morphology evolving from continuous one to serrated one with the cutting speed increasing from 100-1500m/min is observed. Compared with the continuous chip pattern, serrated chip has its particular characterization parameters. The characteristics of serration degree and the segmentation frequency of the serrated chip are presented. The micro-hardness at the adiabatic shear band of serrated chip is then measured. The results show that the serration degree and segmentation frequency of serrated chip have a tendency of enhancement with the cutting speed increasing. The micro-hardness along the adiabatic shear band increases with the cutting speed increasing due to severe strain hardening. With a critical speed at about 100-200m/min, micro-hardness decreases from the tool-chip interface to the free surface of the chip.

The Aerodynamic Development of a Highly Loaded Nozzle Guide Vane

1986 ◽  
Vol 108 (2) ◽  
pp. 261-268 ◽  
Author(s):  
N. C. Baines ◽  
M. L. G. Oldfield ◽  
J. P. Simons ◽  
J. M. Wright
Keyword(s):  
Boundary Layer ◽  
High Speed ◽  
Guide Vane ◽  
Layer Growth ◽  
Suction Surface ◽  
Pressure Surface ◽  
Unsteady Separation ◽  
Surface Contour ◽  
Boundary Layer Development ◽  
Nozzle Guide

A series of high-pressure turbine nozzle guide vanes has been designed for progressively increasing blade loading and reduction in blade solidity without additional loss penalty. Early members of the series achieved this by changes to the suction surface contour, but for the latest design the pressure surface contour was extensively modified to reduce the velocities on this surface substantially. Cascade testing revealed that this vane had a higher loss than its predecessor, and this appears to be largely due to a long region of boundary layer growth on the suction surface and possibly also an unsteady separation. These tests demonstrated the value of a flattened pitot tube held against the blade surface in determining the boundary layer state. By using a pitot probe of only modest frequency response (of order 100 Hz) it was possible to observe significant qualitative differences in the raw signals from laminar, transitional and turbulent boundary layers, which have previously been observed only with much higher frequency instruments. The test results include a comparison of boundary layer measurements on the same cascade test section in two different high-speed wind tunnels. This comparison suggests that freestream turbulence can have a large effect on boundary layer development and 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.

Study on Chip Morphology and Adiabatic Shear in High Speed Cutting of Alloy Steels with Different Hardness

2010 ◽  
Vol 26-28 ◽  
pp. 875-879
Author(s):  
Chun Zheng Duan ◽  
Hong Hua Li ◽  
Min Jie Wang ◽  
Yu Jun Cai
Keyword(s):  
Shear Band ◽  
High Speed ◽  
Adiabatic Shear Band ◽  
Shear Bands ◽  
Cutting Speed ◽  
Chip Morphology ◽  
Optical Microscope ◽  
Adiabatic Shear ◽  
Serrated Chip ◽  
High Speed Cutting

The chip morphology and the formation and development of the adiabatic shear band within the serrated chips formed in high speed cutting of 30CrNi3MoV steel with two tempering hardness were observed and analyzed using optical microscope and SEM. The investigation shows that as the adiabatic shear phenomenon occurs and develops, the chip morphology changes as follows: ribbon chip→serrated chip with deformed band→serrated chip with transformed band→fractured chip. The cutting speed and tempering hardness is the two main factors affecting adiabatic shear, in the case of lower cutting speed the formation and development of adiabatic shear band are more sensitive to tempered hardness increase. The deformed shear bands are constituted by large deformed microstructure, while the formation of the transformed shear bands has experienced the large plastic deformation and grain refinement.

Component Analysis of Adiabatic Shear Band Formed in High Speed Cutting of High Strength Alloy Steel

2011 ◽  
Vol 52-54 ◽  
pp. 1482-1485
Author(s):  
Chun Zheng Duan ◽  
Zhao Xi Wang ◽  
Min Jie Wang ◽  
Wei Sen Kong
Keyword(s):  
Shear Band ◽  
High Speed ◽  
Adiabatic Shear Band ◽  
Diffusion Mechanism ◽  
Shear Bands ◽  
Cutting Speed ◽  
High Strength ◽  
Adiabatic Shear ◽  
Serrated Chip ◽  
High Speed Cutting

The component distribution of adiabatic shear banding during high speed cutting(HSC) is important to understand the phase transformation during formation of adiabatic shear band and mechanism of serrated chip formation. This paper analyzed element distribution inside and near the adiabatic shear bands formed during HSC of 30CrNi3MoV high strength steel using electronic probe. It was found that there is no obvious element segregation, but carbon element tends to gather towards adiabatic shear band’s boundaries. The density of carbon inside the shear bands tends to increase with the increase of cutting speed. The results indicated that the diffusion and gather of carbon may occur during formation of adiabatic shear band. The diffusion mechanism may be short-range diffusion driven by high-speed deformation and high temperature rise.

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