Clear band formation simulated by dislocation dynamics: Role of helical turns and pile-ups

2008 ◽  
Vol 380 (1-3) ◽  
pp. 22-29 ◽  
Author(s):  
Thomas Nogaret ◽  
David Rodney ◽  
Marc Fivel ◽  
Christian Robertson
Keyword(s):  
Dislocation Dynamics ◽  
Band Formation ◽  
Clear Band

scholarly journals Dzyaloshinskii–Moriya interaction in noncentrosymmetric superlattices

2021 ◽  
Vol 7 (1) ◽  
Author(s):  
Woo Seung Ham ◽  
Abdul-Muizz Pradipto ◽  
Kay Yakushiji ◽  
Kwangsu Kim ◽  
Sonny H. Rhim ◽  
...  
Keyword(s):  
Heavy Metal ◽  
Degrees Of Freedom ◽  
Orbit Coupling ◽  
Inversion Symmetry ◽  
Spin Orbit Coupling ◽  
Spin Orbit ◽  
Band Formation ◽  
Research Activities ◽  
Moriya Interaction

AbstractDzyaloshinskii–Moriya interaction (DMI) is considered as one of the most important energies for specific chiral textures such as magnetic skyrmions. The keys of generating DMI are the absence of structural inversion symmetry and exchange energy with spin–orbit coupling. Therefore, a vast majority of research activities about DMI are mainly limited to heavy metal/ferromagnet bilayer systems, only focusing on their interfaces. Here, we report an asymmetric band formation in a superlattices (SL) which arises from inversion symmetry breaking in stacking order of atomic layers, implying the role of bulk-like contribution. Such bulk DMI is more than 300% larger than simple sum of interfacial contribution. Moreover, the asymmetric band is largely affected by strong spin–orbit coupling, showing crucial role of a heavy metal even in the non-interfacial origin of DMI. Our work provides more degrees of freedom to design chiral magnets for spintronics applications.

scholarly journals Boosting the Seebeck Coefficient for Organic Coordination Polymers: Role of Doping-Induced Polaron Band Formation

2019 ◽  
Vol 10 (10) ◽  
pp. 2493-2499 ◽  
Author(s):  
Yunpeng Liu ◽  
Wen Shi ◽  
Tianqi Zhao ◽  
Dong Wang ◽  
Zhigang Shuai
Keyword(s):  
Seebeck Coefficient ◽  
Coordination Polymers ◽  
Band Formation ◽  
Polaron Band

Onset of the Portevin-Le Chatelier Effect: Role of Synchronization of Dislocations

2014 ◽  
Vol 783-786 ◽  
pp. 198-203 ◽  
Author(s):  
Tatiana Lebedkina ◽  
Nikolay P. Kobelev ◽  
Mikhail Lebyodkin
Keyword(s):  
Flow Stress ◽  
Strain Rate ◽  
Collective Motion ◽  
Rate Sensitivity ◽  
Plastic Instability ◽  
Strain Rate Range ◽  
Dislocation Dynamics ◽  
Transient Kinetics ◽  
Kinetic Measurements

The problem of the onset of the Portevin-Le Chatelier (PLC) effect is revised by combining a study of the kinetics of the flow stress evolution upon abrupt changes in the applied strain rate and acoustic emission (AE) accompanying plastic deformation of an AlMg alloy. The kinetic measurements allow evaluating the strain-rate sensitivity of the flow stress and the time characteristics of transient processes as functions of plastic strain. Using known criteria of plastic instability, domains of instability are constructed in the (strain, strain rate) plane. A particular accent is put on the strain-rate range corresponding to the so-called “inverse” behavior. The comparison of such maps with experimental data on the critical strain testifies to the insufficiency of these criteria for explaining the onset of the PLC effect. Moreover, the slow transient kinetics contradicts observations of the fast development of stress drops. The AE measurements bear witness that the stress serrations are associated with bursts in duration of acoustic events generated by the collective motion of dislocations. The possible role of synchronization of dislocation dynamics on the onset of plastic instability is discussed.

scholarly journals Axial-Compressive Behavior, Including Kink-Band Formation and Propagation, of Singlep-Phenylene Terephthalamide (PPTA) Fibers

2013 ◽  
Vol 2013 ◽  
pp. 1-15 ◽  
Author(s):  
M. Grujicic ◽  
S. Ramaswami ◽  
J. S. Snipes ◽  
R. Yavari ◽  
C.-F. Yen ◽  
...  
Keyword(s):  
Detrimental Effect ◽  
Mechanical Response ◽  
Topological Defects ◽  
Kink Band ◽  
Coarse Grained ◽  
Computational Investigation ◽  
Band Formation ◽  
Longitudinal Tensile Strength ◽  
Kink Bands

The mechanical response ofp-phenylene terephthalamide (PPTA) single fibers when subjected to uniaxial compression is investigated computationally using coarse-grained molecular statics/dynamics methods. In order to construct the coarse-grained PPTA model (specifically, in order to define the nature of the coarse-grained particles/beads and to parameterize various components of the bead/bead force-field functions), the results of an all-atom molecular-level computational investigation are used. In addition, the microstructure/topology of the fiber core, consisting of a number of coaxial crystalline fibrils, is taken into account. Also, following our prior work, various PPTA crystallographic/topological defects are introduced into the model (at concentrations consistent with the prototypical PPTA synthesis/processing conditions). The analysis carried out clearly revealed (a) formation of the kink bands during axial compression; (b) the role of defects in promoting the formation of kink bands; (c) the stimulating effects of some defects on the fiber-fibrillation process; and (d) the detrimental effect of the prior compression, associated with fiber fibrillation, on the residual longitudinal-tensile strength of the PPTA fibers.

Selected Expression and Functional Importance of α4a-Tubulin in Platelet Biogenesis

Blood ◽  
2016 ◽  
Vol 128 (22) ◽  
pp. 1360-1360
Author(s):  
Catherine Strassel ◽  
Agnes Hovasse ◽  
Sylvie Moog ◽  
Magda Mageira ◽  
Morgane Batzenschlager ◽  
...  
Keyword(s):  
Conflicts Of Interest ◽  
Human Platelets ◽  
Band Formation ◽  
Acetylated Tubulin ◽  
New Information ◽  
Tubulin Isotype ◽  
Tubulin Isoforms ◽  
Marginal Band ◽  
Platelet Formation

Abstract Platelets are produced from mature megakaryocytes (MK) following a profound cellular reorganization. This includes the assembly of microtubules (MT) into a unique submenbranous coiled structure, the marginal band (MB). This process is thought to depend on a specific αβ-tubulin isotype repertoire. The MK-restricted-β1-tubulin, the predominant isoform of the MB, is already known to be important for platelet biogenesis but the implication of other isotypes is currently unknown. Our goal was to establish the αβ-tubulin repertoire in platelets and during megakaryopoiesis and to evaluate the implication of selected isotypes in platelet formation. To establish an exhaustive list of the tubulin isotypes, we used combination of RT PCR and proteomic analyses to quantify the expression of each isotype in human platelets and in human MK differentiated in culture from CD34+ hematopoietic progenitors. Information gained on the hierarchical combination of tubulin isoforms in the course of platelet biogenesis has been extended at the functional level to investigate both their role in marginal band formation and platelet functions β6-, β5- and α1c-tubulin transcripts were already present in CD34+ cells and decreased during the final stages of megakaryopoiesis. On the other hand, β1-, α4A- and α8-tubulin transcripts were only observed later during MK differentiation and in platelets. Quantitative LC-SRM mass spectrometry confirmed the predominant expression of β1 and α4A-isotypes in platelets. A functional role of the newly identified α4a-tubulin was supported by the thrombocytopenia and enlarged platelets with a decreased number of MT coils (1-3) comprising less-acetylated tubulin in mice carrying a point mutation in tuba4a. Additionally, a tendency to increased responses to several agonists was observed in these platelets. This study reveals new information on the evolution of the tubulin isotype repertoire in platelet formation pointing to a role of less-widely expressed α-isotypes. Disclosures No relevant conflicts of interest to declare.

Mechanics and Dislocation Structures at the Micro-Scale: Insights on Dislocation Multiplication Mechanisms from Discrete Dislocation Dynamics Simulations

2014 ◽  
Vol 1651 ◽  
Author(s):  
D. Weygand
Keyword(s):  
Dislocation Dynamics ◽  
Discrete Dislocation Dynamics ◽  
Relative Contribution ◽  
Discrete Dislocation ◽  
Dynamics Simulations ◽  
Stress Drops ◽  
Dislocation Sources ◽  
Continuum Theories ◽  
Dislocation Multiplication

ABSTRACTThe plasticity of micro-pillar deformation has widely been studied by discrete dislocation dynamics simulations to explain the so-called size effect. In this study the role of glissile junctions forming during plastic deformation under various loading scenarios is in the center of interest. The activity of these naturally forming dislocation sources is followed in detail. Surprisingly these junctions are rather active sources and not just another obstacle as often assumed. Their relative contribution to the overall dislocation density for the simulated specimens reaches often values of 20% or even more. The formation of such a glissile junction is often correlated to stress drops or the end of a stress drop. It is therefore suggested – at least for the sample sizes considered – that this dislocation multiplication mechanism should be take into account in continuum models such as crystal plasticity of higher order dislocation continuum theories.

The Role of Homogeneous Nucleation in Planar Dynamic Discrete Dislocation Plasticity

2015 ◽  
Vol 82 (7) ◽  
Author(s):  
Benat Gurrutxaga-Lerma ◽  
Daniel S. Balint ◽  
Daniele Dini ◽  
Daniel E. Eakins ◽  
Adrian P. Sutton
Keyword(s):  
Homogeneous Nucleation ◽  
Dislocation Dynamics ◽  
Plastic Relaxation ◽  
Strain Rates ◽  
Dislocation Generation ◽  
Discrete Dislocation Dynamics ◽  
Discrete Dislocation ◽  
Dislocation Plasticity ◽  
Dislocation Densities

Homogeneous nucleation of dislocations is the dominant dislocation generation mechanism at strain rates above 108 s−1; at those rates, homogeneous nucleation dominates the plastic relaxation of shock waves in the same way that Frank–Read sources control the onset of plastic flow at low strain rates. This article describes the implementation of homogeneous nucleation in dynamic discrete dislocation plasticity (D3P), a planar method of discrete dislocation dynamics (DDD) that offers a complete elastodynamic treatment of plasticity. The implemented methodology is put to the test by studying four materials—Al, Fe, Ni, and Mo—that are shock loaded with the same intensity and a strain rate of 1010 s−1. It is found that, even for comparable dislocation densities, the lattice shear strength is fundamental in determining the amount of plastic relaxation a material displays when shock loaded.

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