Influence of Preheating on Chip Segmentation and Microstructure in Orthogonal Machining of Ti6Al4V

2013 ◽  
Vol 135 (6) ◽  
Author(s):  
Shashikant Joshi ◽  
Asim Tewari ◽  
Suhas Joshi
Keyword(s):  
Shear Band ◽  
Cutting Forces ◽  
Conceptual Models ◽  
Shear Bands ◽  
Shear Plane ◽  
Band Formation ◽  
Orthogonal Machining ◽  
On Chip ◽  
Compressive Residual Stresses ◽  
Machined Surfaces

Chip segmentation due to shear localization during machining of titanium alloys affects cutting forces and their machinability. Despite several studies on modeling and understanding influence of chip segmentation, little is known about the effect of preheating on it. This work therefore, involves orthogonal machining of Ti6Al4V alloy under preheating between 100 °C and 350 °C to investigate chip segmentation, shear band configuration, and microstructure of machined surfaces, through optical and scanning electron microscopy of chips and chip roots. Conceptual models of chip segment formation have been evolved. Shear band formation appears to be the dominant mechanism of chip segmentation up to 260 °C preheating, however at 350 °C, extent of fracture along the shear plane increases. The preheating increases spacing between shear bands in chips, reduces shear band thickness from 21 μm at 100 °C to 8 μm at 350 °C, and ultimately reduces cutting forces fluctuation, and compressive residual stresses in the machined surfaces.

Microstructural Characterization of Chip Segmentation Under Different Machining Environments in Orthogonal Machining of Ti6Al4V

2015 ◽  
Vol 137 (1) ◽  
Author(s):  
Shashikant Joshi ◽  
Asim Tewari ◽  
Suhas S. Joshi
Keyword(s):  
Plastic Strain ◽  
Room Temperature ◽  
Microstructural Analysis ◽  
Cutting Speed ◽  
Microstructural Characterization ◽  
Shear Plane ◽  
Band Formation ◽  
Orthogonal Machining ◽  
Two Temperatures ◽  
Experimental Values

Segmented chips are known to form in machining of titanium alloys due to localization of heat in the shear zone, which is a function of machining environment. To investigate the correlation between machining environments and microstructural aspects of chip segmentation, orthogonal turning experiments were performed under three machining environments, viz., room, LN2, and 260 °C. Scanning electron and optical microscopy of chip roots show that the mechanism of chip segment formation changes from plastic strain and mode II fracture at room temperature, to predominant mode I fracture at LN2 and plastic strain leading to shear band formation at 260 °C. The chip segment pitch and shear plane length predicted using Deform™ matched well with the experimental values at room temperature. The microstructural analysis of chips show that higher shear localization occurs at room temperature than the other two temperatures. The depth of machining affected zone (MAZ) on work surfaces was lower at the two temperatures than that of at the room temperature at a higher cutting speed of 91.8 m/min.

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.

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.

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.

On Critical Conditions for Chip Transformation from Continuous to Serrated in High-Speed Machining

2013 ◽  
Vol 589-590 ◽  
pp. 232-237 ◽  
Author(s):  
Guo Sheng Su ◽  
Zhan Qiang Liu
Keyword(s):  
Shear Strain ◽  
High Speed ◽  
Shear Bands ◽  
Cutting Speed ◽  
Shear Plane ◽  
Critical Conditions ◽  
Serrated Chip ◽  
High Cutting Speed ◽  
On Chip ◽  
Serrated Chips

For most of materials, a chip transformation from continuous to serrated takes place at a relative high cutting speed which is called the critical cutting speed (CCS). Serrated chips at CCS have different characteristics from those at higher cutting speeds. In this paper, the chip transformation is analytically investigated. The deformation in the primary shear zone (PSZ) during the transformation is analyzed. The critical shear strain at CCS for chip transformation is proposed. Cutting Experiments are carried out with four metals, and metallographical and morphological investigations on the chip transformation are conducted. The results show that serrated chips can be produced if the shear localization along a shear plane occurs before the shear plane reaches to the middle of PSZ. At CCS, the flow stress of the shear plane passing through the PSZ reaches maximum at the middle of PSZ and then decreases with further straining. The high thickness of localized shear bands makes the serrated chip at CCS look as a wave. At CCS, the shear strain of chip segments is approximately equal to the critical shear strain for chip transformation. Influences of material hardess (brittleness) on chip transformation are also discussed.

Chip Segmentation in Machining: A Study of Deformation Localization Characteristics in Ti6Al4V

2013 ◽  
Author(s):  
Abhijit Chandra ◽  
Pavan Karra ◽  
Adam Bragg ◽  
Jie Wang ◽  
Gap Yong Kim
Keyword(s):  
Shear Band ◽  
Shear Bands ◽  
Shear Plane ◽  
Time Varying ◽  
State Variables ◽  
Dynamics Model ◽  
Deformation Localization ◽  
Additional State ◽  
Nonlinear Dynamics Model ◽  
Band Spacing

Chip segmentation by deformation localization is an important process in a certain range of velocities and might be desirable in reducing cutting forces and by improving chips’ evacuation, whereas few studies of practical criteria to calculate shear band spacing are available in literature. This paper extends nonlinear dynamics model for chip segmentation by allowing time varying orientation of the shear plane that are pronounced in strain hardening materials. The model extends the non-linear dynamics approach with additional state variables to the Burns and Davies approach. The model is simulated numerically to predict the shear bands of the chip. The numerical simulation of the model is compared with experimental observations and is in agreement with experimental observations in Ti6Al4V. This offers guidance to predict shear band spacing of other materials.

Analytical Modeling of Shear Localization in Orthogonal Cutting Processes

2021 ◽  
pp. 1-45
Author(s):  
Mohammadreza Fazlali ◽  
Mauricio Ponga ◽  
Xiaoliang Jin
Keyword(s):  
Shear Band ◽  
Orthogonal Cutting ◽  
Shear Bands ◽  
Chip Morphology ◽  
High Strength ◽  
Shear Localization ◽  
Shear Band Formation ◽  
Workpiece Material ◽  
Band Formation ◽  
Cutting Processes

Abstract This paper presents an analytical thermo-mechanical model of shear localization and shear band formation in orthogonal cutting of high-strength metallic alloys. The deformation process of the workpiece material includes three stages: homogeneous deformation, shear localization, and chip segmentation. A boundary layer analysis is used to analytically predict the temperature, stress, and strain rate variations in the primary shear zone associated with the shear localization. The predictions of shear band spacing and width from the proposed model are verified by experimental characterization of the chip morphology. The rolling of shear bands on the tool rake face is discussed from the experimental observations. The cutting tool temperature, which is influenced by the heat generated during the shear band formation, is simulated and compared with the finite element simulations. The proposed analytical model reveals the fundamental mechanism of the complete shear localization process in orthogonal cutting, and predicts the stress and temperature variations with high computational efficiency.

Influence of Strain Rate on Shear Localization during Deformation and Fracture of 5754 and 5182 Aluminium Alloy

2006 ◽  
Vol 519-521 ◽  
pp. 1047-1052 ◽  
Author(s):  
Mohammad Jaffar Hadianfard ◽  
Michael J. Worswick
Keyword(s):  
Plastic Deformation ◽  
Shear Band ◽  
Strain Rate ◽  
Shear Bands ◽  
Tensile Tests ◽  
Material Behavior ◽  
Damage Development ◽  
Band Formation ◽  
Deformation And Fracture ◽  
Localized Plastic Deformation

The effect of strain rate in the range of 10-4 to 10-1 s-1 on localization of deformation and fracture behavior of 5754 and 5182 aluminum alloys is investigated. For this study, tensile tests, interrupted tensile tests, shear band decoration, fractography and image analysis has been used. This investigation is based on experimental work and observation of the material behavior. Results show that strain rate has some effect on the mechanical properties and deformation stability of the alloys. The area of localized plastic deformation and thickness of the shear bands were found to be sensitive to the strain rate. It was also observed that localization of plastic deformation and shear band formation is an important step in the damage propagation and final fracture of the alloys. Detail of damage development, based upon micrographs of samples interrupted at different stages of straining is presented

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.

Sign in / Sign up

Export Citation Format

Share Document