Special features of the stress field induced by the edge of the plastic shear band near the crystal surface

1999 ◽  
Vol 42 (9) ◽  
pp. 837-843
Author(s):  
S. D. Borisova ◽  
I. I. Naumov
Keyword(s):  
Stress Field ◽  
Shear Band ◽  
Crystal Surface ◽  
Plastic Shear

Quantitative Study of Shear Localization in Chip Formation while Machining Ti-6Al-4V

2009 ◽  
Vol 407-408 ◽  
pp. 412-415
Author(s):  
Dong Liu ◽  
Wu Yi Chen ◽  
Hong Hai Xu ◽  
Xue Ke Luo ◽  
Hui Liang
Keyword(s):  
Shear Band ◽  
Shear Flow ◽  
Quantitative Study ◽  
Cutting Speed ◽  
Optical Microscope ◽  
Shear Localization ◽  
Adiabatic Shear ◽  
Plastic Shear ◽  
Orthogonal Machining ◽  
Cutting Speeds

The formation of shear localized chips in orthogonal machining of Ti-6Al-4V was investigated. The chips in different cutting velocities were collected and the structure of the adiabatic shear localization was examined by optical microscope and SEM after polishing and eroding. The serrated coefficient, serrated frequency and fibred coefficient were proposed in this paper to characterize the degree of serration and plastic shear flow of the chip quantitatively. Experimental results show that the width of the shear band decreased and the fibred coefficient of the shear band increased as cutting speed increased. The serrated and frequency, the serrated coefficient increased with the increase of cutting speed in the experimental range of cutting speeds.

scholarly journals A Thermo-Poro-Visco-Plastic Shear Band Model for Seismic Triggering and Evolution of Catastrophic Landslides

2007 ◽  
Vol 47 (1) ◽  
pp. 11-25 ◽  
Author(s):  
Nikos Gerolymos ◽  
Ioannis Vardoulakis ◽  
George Gazetas
Keyword(s):  
Shear Band ◽  
Band Model ◽  
Plastic Shear ◽  
Seismic Triggering

Propagation of shear bands in a Cu47.5Zr47.5Al5 bulk metallic glass

2008 ◽  
Vol 23 (1) ◽  
pp. 6-12 ◽  
Author(s):  
K.B. Kim ◽  
J. Das ◽  
M.H. Lee ◽  
S. Yi ◽  
E. Fleury ◽  
...  
Keyword(s):  
Fracture Surface ◽  
Stress Field ◽  
Shear Band ◽  
Metallic Glass ◽  
Bulk Metallic Glass ◽  
Elastic Properties ◽  
Work Hardening ◽  
Shear Bands ◽  
Propagation Mode ◽  
Cast State

We report a novel finding of slither propagation of shear bands on the fracture surface of a Cu47.5Zr47.5Al5 bulk metallic glass (BMG). The nanoscale heterogeneities in the as-cast state are aggregated along shear bands with irregular morphology. Such heterogeneities create a fluctuating stress field during shear band propagation leading to a slither propagation mode. The slither propagation of 10 to 15 nm wide shear bands is effective to improve both the plasticity and the “work-hardening-like” behavior of BMGs if the size, the morphology, and the elastic properties of the heterogeneities are intimately intercalated during solidification.

On evolution of thermo-plastic shear band

1986 ◽  
Vol 2 (1) ◽  
pp. 1-7 ◽  
Author(s):  
Bai Yilong ◽  
Cheng Chemin ◽  
Yu Shanbing
Keyword(s):  
Shear Band ◽  
Plastic Shear

Convergent Beam Electron Diffraction

1978 ◽  
Vol 36 (3) ◽  
pp. 304-315
Author(s):  
G. Lehmpfuhl
Keyword(s):  
Electron Diffraction ◽  
Diffraction Pattern ◽  
Crystal Surface ◽  
Diffraction Spot ◽  
Crystal Thickness ◽  
Large Area ◽  
Electron Microscopic ◽  
Additional Information ◽  
Microscopic Investigations

Introduction In electron microscopic investigations of crystalline specimens the direct observation of the electron diffraction pattern gives additional information about the specimen. The quality of this information depends on the quality of the crystals or the crystal area contributing to the diffraction pattern. By selected area diffraction in a conventional electron microscope, specimen areas as small as 1 µ in diameter can be investigated. It is well known that crystal areas of that size which must be thin enough (in the order of 1000 Å) for electron microscopic investigations are normally somewhat distorted by bending, or they are not homogeneous. Furthermore, the crystal surface is not well defined over such a large area. These are facts which cause reduction of information in the diffraction pattern. The intensity of a diffraction spot, for example, depends on the crystal thickness. If the thickness is not uniform over the investigated area, one observes an averaged intensity, so that the intensity distribution in the diffraction pattern cannot be used for an analysis unless additional information is available.

Crystal Structure Determination of Glycerol-Containing Lipids from Electron Diffraction Data. Use of Analog Compounds Based upon Configurational Isomers of Cyclopentane-1, 2, 3-TRIOL

1977 ◽  
Vol 35 ◽  
pp. 24-25
Author(s):  
Douglas L. Dorset ◽  
Anthony J. Hancock
Keyword(s):  
Crystal Structure ◽  
Electron Diffraction ◽  
Diffraction Data ◽  
Structure Determination ◽  
Crystal Surface ◽  
Coherent Scattering ◽  
Crystal Structure Determination ◽  
Electron Diffraction Data ◽  
Polar Group ◽  
Axis Orientation

Lipids containing long polymethylene chains were among the first compounds subjected to electron diffraction structure analysis. It was only recently realized, however, that various distortions of thin lipid microcrystal plates, e.g. bends, polar group and methyl end plane disorders, etc. (1-3), restrict coherent scattering to the methylene subcell alone, particularly if undistorted molecular layers have well-defined end planes. Thus, ab initio crystal structure determination on a given single uncharacterized natural lipid using electron diffraction data can only hope to identify the subcell packing and the chain axis orientation with respect to the crystal surface. In lipids based on glycerol, for example, conformations of long chains and polar groups about the C-C bonds of this moiety still would remain unknown.One possible means of surmounting this difficulty is to investigate structural analogs of the material of interest in conjunction with the natural compound itself. Suitable analogs to the glycerol lipids are compounds based on the three configurational isomers of cyclopentane-1,2,3-triol shown in Fig. 1, in which three rotameric forms of the natural glycerol derivatives are fixed by the ring structure (4-7).

Studies of Oxide Formation on Copper Thin Films by Electron Microscopy

1977 ◽  
Vol 35 ◽  
pp. 316-317
Author(s):  
G. G. Hembree ◽  
M. A. Otooni ◽  
J. M. Cowley
Keyword(s):  
Electron Microscopy ◽  
Electron Diffraction ◽  
Single Crystal ◽  
Crystal Surface ◽  
Crystal Defects ◽  
Diffraction Reflection ◽  
Reaction Products ◽  
Intermediate Energies ◽  
Crystal Films ◽  
Reflection Electron Microscopy

The formation of oxide structures on single crystal films of metals has been investigated using the REMEDIE system (for Reflection Electron Microscopy and Electron Diffraction at Intermediate Energies) (1). Using this instrument scanning images can be obtained with a 5 to 15keV incident electron beam by collecting either secondary or diffracted electrons from the crystal surface (2). It is particularly suited to studies of the present sort where the surface reactions are strongly related to surface morphology and crystal defects and the growth of reaction products is inhomogeneous and not adequately described in terms of a single parameter. Observation of the samples has also been made by reflection electron diffraction, reflection electron microscopy and replication techniques in a JEM-100B electron microscope.A thin single crystal film of copper, epitaxially grown on NaCl of (100) orientation, was repositioned on a large copper single crystal of (111) orientation.

Structure and migration of planar defects in crystals observed in atomic scale

1978 ◽  
Vol 36 (1) ◽  
pp. 284-285 ◽  
Author(s):  
H. Hashimoto ◽  
Y. Sugimoto ◽  
Y. Takai ◽  
H. Endoh
Keyword(s):  
Electron Microscope ◽  
Rotation Angle ◽  
Crystal Surface ◽  
Electron Gun ◽  
Atomic Scale ◽  
Present Observation ◽  
Twist Boundary ◽  
Optical Magnification ◽  
Zinc Crystal ◽  
And Migration

As was demonstrated by the present authors that atomic structure of simple crystal can be photographed by the conventional 100 kV electron microscope adjusted at “aberration free focus (AFF)” condition. In order to operate the microscope at AFF condition effectively, highly stabilized electron beams with small energy spread and small beam divergence are necessary. In the present observation, a 120 kV electron microscope with LaB6 electron gun was used. The most of the images were taken with the direct electron optical magnification of 1.3 million times and then magnified photographically.1. Twist boundary of ZnSFig. 1 is the image of wurtzite single crystal with twist boundary grown on the surface of zinc crystal by the reaction of sulphur vapour of 1540 Torr at 500°C. Crystal surface is parallel to (00.1) plane and electron beam is incident along the axis normal to the crystal surface. In the twist boundary there is a dislocation net work between two perfect crystals with a certain rotation angle.

Contrast in Scanning Images of Thin Crystals

1972 ◽  
Vol 30 ◽  
pp. 520-521
Author(s):  
S. Kimoto ◽  
H. Hashimoto ◽  
S. Takashima ◽  
R. M. Stern ◽  
T. Ichinokawa
Keyword(s):  
Crystal Surface ◽  
Solid Angle ◽  
Incident Angle ◽  
Intensity Variation ◽  
Lattice Defects ◽  
Scanning Microscope ◽  
Electron Detector ◽  
Backscattered Electrons ◽  
Electron Image ◽  
Backscattered Electron

The most well known application of the scanning microscope to the crystals is known as Coates pattern. The contrast of this image depends on the variation of the incident angle of the beam to the crystal surface. The defect in the crystal surface causes to make contrast in normal scanning image with constant incident angle. The intensity variation of the backscattered electrons in the scanning microscopy was calculated for the defect in the crystals by Clarke and Howie. Clarke also observed the defect using a scanning microscope.This paper reports the observation of lattice defects appears in thin crystals through backscattered, secondary and transmitted electron image. As a backscattered electron detector, a p-n junction detector of 0.9 π solid angle has been prepared for JSM-50A. The gain of the detector itself is 1.2 x 104 at 50 kV and the gain of additional AC amplifier using band width 100 Hz ∼ 10 kHz is 106.

Observation of secondary slip systems in tungsten bicrystals

1984 ◽  
Vol 42 ◽  
pp. 478-479
Author(s):  
J. R. Fekete ◽  
R. Gibala
Keyword(s):  
Stress Field ◽  
Grain Boundaries ◽  
Deformation Behavior ◽  
Stress Axis ◽  
Polycrystalline Materials ◽  
Slip Systems ◽  
Metallic Materials ◽  
Twist Boundary ◽  
Secondary Slip ◽  
Plane Normal

The deformation behavior of metallic materials is modified by the presence of grain boundaries. When polycrystalline materials are deformed, additional stresses over and above those externally imposed on the material are induced. These stresses result from the constraint of the grain boundaries on the deformation of incompatible grains. This incompatibility can be elastic or plastic in nature. One of the mechanisms by which these stresses can be relieved is the activation of secondary slip systems. Secondary slip systems have been shown to relieve elastic and plastic compatibility stresses. The deformation of tungsten bicrystals is interesting, due to the elastic isotropy of the material, which implies that the entire compatibility stress field will exist due to plastic incompatibility. The work described here shows TEM observations of the activation of secondary slip in tungsten bicrystals with a [110] twist boundary oriented with the plane normal parallel to the stress axis.

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