Defect Structure Parameters of Deformed Polycrystals on Micro- and Mesolevel of Grain Sizes

2014 ◽  
Vol 1013 ◽  
pp. 1-6
Author(s):  
Eduard Kozlov ◽  
Natal'ya Popova ◽  
Marina Fedorischeva ◽  
Nina Koneva
Keyword(s):  
Plastic Deformation ◽  
Size Effect ◽  
Defect Structure ◽  
Structure Parameters ◽  
Scalar Density ◽  
Grain Sizes ◽  
Different Types ◽  
Closed Structure ◽  
Mechanisms Of Plastic Deformation

In the paper we consider the size effect of the closed structural formations as the function of accumulation of scalar density dislocations and their components under plastic deformation. The focus is on the role of interfaces of different types. The sizes are determined and the various parameters of the structure defining the micro-and mesolevel are identified at the development of the mechanisms of plastic deformation. The role of statistically stored dislocations (SSD) and geometrically necessary dislocations (GND) in the formation of the defect structure of the material is examined. It has been established that the smaller the size of the closed structure, the greater the GND part and the smaller the SSD component. The work is based on the TEM research of the structure of deformed materials.

Effect of a Surface Constraining Layer on the Plastic Deformation of Au Microspheres

MRS Advances ◽  
2018 ◽  
Vol 3 (8-9) ◽  
pp. 427-432
Author(s):  
AZM Ariful Islam ◽  
Robert J. Klassen
Keyword(s):  
Plastic Deformation ◽  
Small Volume ◽  
Dislocation Nucleation ◽  
Surface Layers ◽  
Loading Rates ◽  
Plastic Deformation Process ◽  
Sputter Deposited ◽  
Yield Force ◽  
Mechanisms Of Plastic Deformation

ABSTRACTSingle crystal Au microspheres, of 3 μm diameter, with sputter-deposited Ni surface layers, of 40 or 80 nm thickness, were tested in compression at three loading rates to investigate the role of thin passive layers on the mechanisms of plastic deformation of small-volume FCC ductile metal samples. The Ni layer resulted in an increase in the incipient yield force by about 10%. Micro-cracking of the Ni layer was observed to occur with incipient yielding. The estimated apparent activation volume of the incipient plastic deformation process was found to be nearly identical for the Ni-coated and the uncoated Au microspheres. This suggests that, while the stress required to initiate incipient plastic deformation was increased by the constraint imposed by the Ni layer, the subsequent plastic flow occurred by a dislocation nucleation and glide mechanism that is essentially the same as that occurring in an unconstrained Au microsphere.

scholarly journals Nucleation and development of plasticity in nanocrystalline BCC iron under shear loading

2020 ◽  
pp. 17-22
Author(s):  
K.P. Zolnikov ◽  
◽  
D.S. Kryzhevich ◽  
A.V. Korchuganov ◽  
◽  
...  
Keyword(s):  
Plastic Deformation ◽  
Shear Loading ◽  
Main Role ◽  
Structural Rearrangements ◽  
Second Stage ◽  
Grain Sizes ◽  
Bcc Lattice ◽  
Bcc Iron ◽  
Nanocrystalline Iron ◽  
Mechanisms Of Plastic Deformation

The features of the nucleation and development of plasticity in nanocrystalline iron with BCC lattice under shear were studied. The mechanisms of plastic deformation playing the main role in the development of structural rearrangements during loading were revealed. It was shown that the development of plasticity can be conditionally divided into several stages. The first stage of plasticity development is associated with the formation and propagation of dislocations and twins. At the second stage, intraganular slip and intergranular sliding begin to make the main contribution to plastic deformation. These processes initiate a change in the shape of the grains. At large shear, the deformation behavior of the sample is governed by the migration of the interfaces. Not only grain boundaries migrate but also twin ones do. As a result of migration processes, the grain sizes of the nanocrystalline sample are enlarged.

scholarly journals Influence of grain size on mechanisms of plastic deformation and yield stress

2020 ◽  
Vol 2020 (1) ◽  
pp. 26-32
Author(s):  
K. M. Borysovska ◽  
◽  
Y.M. Podrezov ◽  
S.O. Firstov ◽  
◽  
...  
Keyword(s):  
Plastic Deformation ◽  
Grain Size ◽  
Yield Strength ◽  
Plastic Flow ◽  
Major Influence ◽  
Entire Cross Section ◽  
Physical Yield ◽  
Grain Sizes ◽  
20 Nm ◽  
Mechanisms Of Plastic Deformation

The influence of grain size on the physical yield strength of the polycrystal is considered by the method of cellular automata. The physical yield strength of the polycrystal in this model is defined as the stress at which, the plastic deformation covers the entire cross section of the sample from one edge to another. Three mechanisms of plastic deformation are considered. The first one is an initiation of plastic flow from grain to grain by dislocation pile-ups. The second one is plastic flow in different grains independently of each other under the action of external stress and the third one is intergranular slippage. Computer simulations have shown that at large grain sizes (d > 200 nm) deformation propagates from grain to grain by initiating dislocations pile-ups, since in this case pile-ups are quite powerful and have a large effect on neighboring grains. At average values of grain size (20 nm <d <200 nm) plastic deformation occurs in the grains independently of each other, and the external strain give a major influence on plastic deformation. With further reduction of the grain sizes (d <20 nm) the main mechanism of deformation is intergranular slippage. because in grains of this size are quite large image stresses that do not allow large dislocation clusters. In small grains the image forces are quite large to prevent large dislocation pile-ups formation, but the mass and volume of grain are quite small to turn or slip its under the action of external stresses. In accordance with these mechanisms, on the calculated dependence of the physical yield strength vs grain size, there are three areas with different angles of inclination in logarithmic coordinates. Keywords: yield point, grain size, Hall―Petch low.

Performance Analysis of Hydrostatic Slideways Systems with Different Types of Restrictors

2011 ◽  
Vol 474-476 ◽  
pp. 1661-1665
Author(s):  
Sheng Hao Zhou ◽  
Jin Chun Song ◽  
Zhi Wei Zhang ◽  
Song Li
Keyword(s):  
Machine Tools ◽  
Structure Parameters ◽  
Dynamic Feedback ◽  
Feedback Type ◽  
Closed Type ◽  
Stiffness Model ◽  
Different Types ◽  
Capillary Type ◽  
Film Stiffness

In fluid hydrostatic closed-type slideways systems, restrictor will take an important role of improving the performance of machine tools. Generally there are four types of restrictors to be utilized, capillary type, orifice type, slot type, and dynamic feedback type. The general oil film stiffness model of different types of restrictors was constructed and the characteristics of different types of restrictors are analyzed and compared. The analysis results demonstrated that the stiffness of restrictors depend on the geometry and structure parameters, and according to the analysis results the all types of restrictors can be designed optimally.

Computer Simulation for X-Ray Analysis of Nanostructured Cu Processed by Severe Plastic Deformation

2004 ◽  
Vol 443-444 ◽  
pp. 99-102
Author(s):  
Nariman A. Enikeev ◽  
Igor V. Alexandrov ◽  
Ruslan Valiev
Keyword(s):  
Experimental Data ◽  
Computer Simulation ◽  
Plastic Deformation ◽  
Grain Boundary ◽  
Severe Plastic Deformation ◽  
Defect Structure ◽  
Structure Parameters ◽  
X Ray ◽  
Simulation Based ◽  
Structure Of Nanomaterials

A computer simulation-based approach has been developed in order to reveal grain boundary defect structure of nanomaterials, which is described in terms of extrinsic grain boundary dislocations. On the basis of comparative analysis of numerically obtained results to experimental data, the defect structure parameters of nanostructured materials produced by severe plastic deformation have been evaluated.

Defect Creation and Photoablation in Stoichiometric and Sub-Stoichiometric SiO2

1985 ◽  
Vol 60 ◽  
Author(s):  
R. A. B. Devine ◽  
C. Fiori
Keyword(s):  
Point Defects ◽  
Defect Structure ◽  
Measurement Techniques ◽  
Electrical Measurement ◽  
Resonance Spectroscopy ◽  
Physical Mechanisms ◽  
Spin Resonance ◽  
Different Types ◽  
Comparison Of The Results

AbstractIt is demonstrated that microscopic point defects can be created in amorphous silica using pulsed ultraviolet irradiation (λ = 248 nm) at energy densities ∼ 100 times less than those normally estimated to lead to damage creation. Identification of the physical character of the defects has been made using electron spin resonance spectroscopy and electrical measurement techniques. Continued irradiation of the SiO2 is found to lead to photoablation. Results obtained for bulk dry SiO2, thermal SiO2 and vacuum deposited SiOx are presented. The important role of non-stoichiometry (defect structure) in the process of photoablation is clearly manifested by comparison of the results obtained for the different types of SiO2. Possible physical mechanisms involved are discussed.

Geometrically Necessary Dislocations in Deformed Martensitic Steel

2014 ◽  
Vol 1013 ◽  
pp. 23-30 ◽  
Author(s):  
Nina Koneva ◽  
Natal'ya Popova ◽  
Marina Fedorischeva ◽  
Eduard Kozlov
Keyword(s):  
Plastic Deformation ◽  
Dislocation Density ◽  
Structure Formation ◽  
Defect Structure ◽  
Martensitic Steel ◽  
Deformation Mechanisms ◽  
Main Attention ◽  
Structural Formation

Effect of a size of closed structural formation on accumulation of dislocation density and its components at plastic deformation is studied. Main attention is given to a role of a division of boundaries of a different type. Structural formation sizes are determined and different parameters of structure defining micro-and mezolevel at development of plastic deformation mechanisms are distinguished. A role of statistically stored dislocations (SSD) and geometrically necessary dislocations (GND) for defect structure formation of a material is examined. It is determined that than a size of closed structural formation is less than that a component of GND is larger and component of SSD is less. The work is based on results of TEM reserches of a structure of deformed materials.

Defect Structure Evolution in HCP-Zirconium Alloys: The Role of Anisotropy

2014 ◽  
Vol 1013 ◽  
pp. 62-66
Author(s):  
Tomara Poletika ◽  
Svetlana Girsova ◽  
Natal'ya Popova ◽  
Eduard Kozlov ◽  
Nina Koneva
Keyword(s):  
Plastic Deformation ◽  
Electron Microscope ◽  
Dislocation Structure ◽  
Defect Structure ◽  
Polycrystalline Material ◽  
Zirconium Alloys ◽  
Structure Evolution ◽  
Internal Stresses

The evolution of the dislocation structure and the ensemble of boundaries during plastic deformation of Zr-Nb alloys studied using electron microscope. The role of the anisotropy of slip in the formation and restructuring of the boundaries, recurrence of dislocation transformation was established. Special emphasis is placed on specific features of geometrically necessary defects evolution. It was found that the geometrically necessary boundaries formation involves an athermal coalescence as a mechanism of relaxation of large accumulated internal stresses, which prevents fracture in an anisotropic polycrystalline material.

Potential Uses of Vinegar as a Medicine and Related in vivo Mechanisms

2016 ◽  
Vol 86 (3-4) ◽  
pp. 127-151 ◽  
Author(s):  
Zeshan Ali ◽  
Zhenbin Wang ◽  
Rai Muhammad Amir ◽  
Shoaib Younas ◽  
Asif Wali ◽  
...  
Keyword(s):  
Chemical Structure ◽  
Review Paper ◽  
Heart Diseases ◽  
Folk Medicine ◽  
Active Role ◽  
Current Review ◽  
Different Types ◽  
Positive Effect

While the use of vinegar to fi ght against infections and other crucial conditions dates back to Hippocrates, recent research has found that vinegar consumption has a positive effect on biomarkers for diabetes, cancer, and heart diseases. Different types of vinegar have been used in the world during different time periods. Vinegar is produced by a fermentation process. Foods with a high content of carbohydrates are a good source of vinegar. Review of the results of different studies performed on vinegar components reveals that the daily use of these components has a healthy impact on the physiological and chemical structure of the human body. During the era of Hippocrates, people used vinegar as a medicine to treat wounds, which means that vinegar is one of the ancient foods used as folk medicine. The purpose of the current review paper is to provide a detailed summary of the outcome of previous studies emphasizing the role of vinegar in treatment of different diseases both in acute and chronic conditions, its in vivo mechanism and the active role of different bacteria.

The Diagnosis of Lupus Anticoagulants by the Activated Partial Thromboplastin Time - The Central Role of Phosphatidyl Serine

1984 ◽  
Vol 52 (02) ◽  
pp. 172-175 ◽  
Author(s):  
P R Kelsey ◽  
K J Stevenson ◽  
L Poller
Keyword(s):  
Screening Method ◽  
Coagulation Factors ◽  
Phosphatidyl Serine ◽  
Test System ◽  
Specific Factor ◽  
Marginal Effect ◽  
Constant Composition ◽  
Lupus Anticoagulants ◽  
Different Types

SummaryLiposomes of pure phospholipids were used in a modified APTT test system and the role of phosphatidyl serine (PS) in determining the sensitivity of the test system to the presence of lupus anticoagulants was assessed. Six consecutive patients with lupus anticoagulants and seven haemophiliacs with anticoagulants directed at specific coagulation factors, were studied. Increasing the concentration of phospholipid in the test system markedly reduced the sensitivity to lupus anticoagulants but had marginal effect on the specific factor inhibitors. The same effect was achieved when the content of PS alone was increased in a vehicle liposome of constant composition.The results suggest that the lupus anticoagulants can best be detected by a screening method using an APTT test with a reagent of low PS content. The use of a reagent rich in PS will largely abolish the lupus anticoagulant’s effect on the APTT. An approach using the two different types of reagent may facilitate differentiation of lupus inhibitors from other types of anticoagulant.

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