scholarly journals Size-dependent energy in crystal plasticity and continuum dislocation models

2015 ◽  
Vol 471 (2175) ◽  
pp. 20140868 ◽  
Author(s):  
Sinisa Dj. Mesarovic ◽  
Samuel Forest ◽  
Jovo P. Jaric
Keyword(s):  
Strong Dependence ◽  
Negative Answer ◽  
Point Of View ◽  
Length Scale ◽  
Dislocation Interaction ◽  
Size Dependent ◽  
Discrete Dislocation ◽  
Dislocation Mechanics ◽  
Dislocation Models ◽  
Dislocation Density Tensor

In the light of recent progress in coarsening the discrete dislocation mechanics, we consider two questions relevant for the development of a mesoscale, size-dependent plasticity: (i) can the phenomenological expression for size-dependent energy, as quadratic form of Nye's dislocation density tensor, be justified from the point of view of dislocation mechanics and under what conditions? (ii) how can physical or phenomenological expressions for size-dependent energy be computed from dislocation mechanics in the general case of elastically anisotropic crystal? The analysis based on material and slip system symmetries implies the negative answer to the first question. However, the coarsening method developed in response to the second question, and based on the physical interpretation of the size-dependent energy as the coarsening error in dislocation interaction energy, introduces additional symmetries. The result is that the equivalence between the phenomenological and the physical expressions is possible, but only if the multiplicity of characteristic lengths associated with different slip systems, is sacrificed. Finally, we discuss the consequences of the assumption that a single length scale governs the plasticity of a crystal, and note that the plastic dissipation at interfaces has a strong dependence on the length scale embedded in the energy expression.

scholarly journals Discrete dislocation plasticity analysis of loading rate-dependent static friction

2016 ◽  
Vol 472 (2192) ◽  
pp. 20150877 ◽  
Author(s):  
H. Song ◽  
V. S. Deshpande ◽  
E. Van der Giessen
Keyword(s):  
Loading Rate ◽  
Static Friction ◽  
Contact Length ◽  
Point Of View ◽  
Size Dependent ◽  
Rate Dependent ◽  
Discrete Dislocation ◽  
Dislocation Plasticity ◽  
Shear Yield ◽  
Contact Size

From a microscopic point of view, the frictional force associated with the relative sliding of rough surfaces originates from deformation of the material in contact, by adhesion in the contact interface or both. We know that plastic deformation at the size scale of micrometres is not only dependent on the size of the contact, but also on the rate of deformation. Moreover, depending on its physical origin, adhesion can also be size and rate dependent, albeit different from plasticity. We present a two-dimensional model that incorporates both discrete dislocation plasticity inside a face-centred cubic crystal and adhesion in the interface to understand the rate dependence of friction caused by micrometre-size asperities. The friction strength is the outcome of the competition between adhesion and discrete dislocation plasticity. As a function of contact size, the friction strength contains two plateaus: at small contact length ( ≲ 0.6   μ m ) , the onset of sliding is fully controlled by adhesion while for large contact length ( ≳ 10   μ m ) , the friction strength approaches the size-independent plastic shear yield strength. The transition regime at intermediate contact size is a result of partial de-cohesion and size-dependent dislocation plasticity, and is determined by dislocation properties, interfacial properties as well as by the loading rate.

scholarly journals Embodied Energy and Embodied GWP of Windows: A Critical Review

Energies ◽  
2021 ◽  
Vol 14 (13) ◽  
pp. 3788
Author(s):  
Francesco Asdrubali ◽  
Marta Roncone ◽  
Gianluca Grazieschi
Keyword(s):  
Critical Analysis ◽  
Strong Dependence ◽  
Primary Energy ◽  
Point Of View ◽  
Embodied Energy ◽  
Construction Sector ◽  
Industrialized Countries ◽  
Different Types ◽  
Operational Phase ◽  
Operational Impact

The construction sector is one of the most energy-intensive in the industrialized countries. In order to limit climate change emissions throughout the entire life cycle of a building, in addition to reducing energy consumption in the operational phase, attention should also be paid to the embodied energy and CO2 emissions of the building itself. The purpose of this work is to review data on embodied energy and GWP derived from EPDs of different types of windows, to identify the LCA phases, the most impacting materials and processes from an environmental point of view and to perform a critical analysis of the outcomes. The results show a strong dependence on the typology of the frame, with wooden windows having competitive performances: lower average primary energy non-renewable (1123 MJ/FU), higher average primary energy renewable (respectively 817 MJ/FU) and lower global warming potential (54 kgCO2eq/FU). More transparency and standardization in the information conveyed by the program operators is, however, desirable for a better comparability of windows performances. In particular, the inclusion of the operational impact in the EPD is sporadic, but strongly important, since it can be the most impactful phase.

scholarly journals Plasticity of crystals and interfaces: From discrete dislocations to size-dependent continuum theory

2010 ◽  
Vol 37 (4) ◽  
pp. 289-332 ◽  
Author(s):  
Sinisa Mesarovic
Keyword(s):  
Unsolved Problem ◽  
Continuum Theory ◽  
Elastic Interaction ◽  
Interface Energy ◽  
Crystalline Materials ◽  
Size Dependent ◽  
Dislocation Mechanics ◽  
Pile Up ◽  
Slip Planes ◽  
Discrete Dislocations

In this communication, we summarize the current advances in size-dependent continuum plasticity of crystals, specifically, the rate-independent (quasistatic) formulation, on the basis of dislocation mechanics. A particular emphasis is placed on relaxation of slip at interfaces. This unsolved problem is the current frontier of research in plasticity of crystalline materials. We outline a framework for further investigation, based on the developed theory for the bulk crystal. The bulk theory is based on the concept of geometrically necessary dislocations, specifically, on configurations where dislocations pile-up against interfaces. The average spacing of slip planes provides a characteristic length for the theory. The physical interpretation of the free energy includes the error in elastic interaction energies resulting from coarse representation of dislocation density fields. Continuum kinematics is determined by the fact that dislocation pile-ups have singular distribution, which allows us to represent the dense dislocation field at the boundary as a superdislocation, i.e., the jump in the slip filed. Associated with this jump is a slip-dependent interface energy, which in turn, makes this formulation suitable for analysis of interface relaxation mechanisms.

scholarly journals Slight pH Fluctuations in the Gold Nanoparticle Synthesis Process Influence the Performance of the Citrate Reduction Method

Sensors ◽  
2018 ◽  
Vol 18 (7) ◽  
pp. 2246 ◽  
Author(s):  
Braulio Contreras-Trigo ◽  
Víctor Díaz-García ◽  
Enrique Guzmán-Gutierrez ◽  
Ignacio Sanhueza ◽  
Pablo Coelho ◽  
...  
Keyword(s):  
Large Scale ◽  
Colloidal Suspension ◽  
Nanoparticle Synthesis ◽  
Trisodium Citrate ◽  
Gold Surface ◽  
Point Of View ◽  
Synthesis Process ◽  
Reaction Yield ◽  
Size Dependent ◽  
Gold Nanoparticle Synthesis

Gold nanoparticles (AuNPs) are currently under intense investigation for biomedical and biotechnology applications, thanks to their ease in preparation, stability, biocompatibility, multiple surface functionalities, and size-dependent optical properties. The most commonly used method for AuNP synthesis in aqueous solution is the reduction of tetrachloroauric acid (HAuCl4) with trisodium citrate. We have observed variations in the pH and in the concentration of the gold colloidal suspension synthesized under standard conditions, verifying a reduction in the reaction yield by around 46% from pH 5.3 (2.4 nM) to pH 4.7 (1.29 nM). Citrate-capped AuNPs were characterized by UV-visible spectroscopy, TEM, EDS, and zeta-potential measurements, revealing a linear correlation between pH and the concentration of the generated AuNPs. This result can be attributed to the adverse effect of protons both on citrate oxidation and on citrate adsorption onto the gold surface, which is required to form the stabilization layer. Overall, this study provides insight into the effect of the pH over the synthesis performance of the method, which would be of particular interest from the point of view of large-scale manufacturing processes.

Multiscale plasticity modeling: coupled atomistics and discrete dislocation mechanics

2004 ◽  
Vol 52 (4) ◽  
pp. 755-787 ◽  
Author(s):  
L.E. Shilkrot ◽  
Ronald E. Miller ◽  
William A. Curtin
Keyword(s):  
Discrete Dislocation ◽  
Dislocation Mechanics

3D Discrete Dislocation Models Of Thin-Film Plasticity

1997 ◽  
Vol 505 ◽  
Author(s):  
A. Hartmaier ◽  
M. C. Fivel ◽  
G. R. Canova ◽  
P. Gumbsch
Keyword(s):  
Thin Film ◽  
Three Dimensional ◽  
Dislocation Dynamics ◽  
Normal Stresses ◽  
Bulk Materials ◽  
Free Standing ◽  
Discrete Dislocation Dynamics ◽  
Discrete Dislocation ◽  
Dislocation Models ◽  
Dimensional Simulation

ABSTRACTThree-dimensional simulation schemes for discrete dislocation dynamics (DDD) have been used successfully to investigate plasticity of bulk materials. The adaptation of these DDD schemes to a description of thin-film plasticity requires detailed modeling of the interfaces and surfaces of the film. One possible method is to compensate for the normal stresses that a dislocation distribution exerts on a surface by appropriate point loads. This traction-compensation method is extended to a free standing film (two opposing surfaces). The extension to a thin film on a substrate is possible.

scholarly journals Discussion On The Ideological And Political Course Of The Basic Course Of Management Specialty Under The Background Of Internet

2021 ◽  
Vol 236 ◽  
pp. 05048
Author(s):  
Shanshan Li ◽  
Xiang Gao ◽  
Xiaoyun Duan
Keyword(s):  
Information Dissemination ◽  
Rapid Development ◽  
Strong Dependence ◽  
Point Of View ◽  
Internet Technology ◽  
Economic Management ◽  
Economic Market ◽  
Life Model ◽  
Comprehensive Literacy ◽  
Set Up

With the rapid development of Internet technology, people's learning and life model has also undergone major changes. The immediacy and efficiency of Internet in information dissemination not only narrow the distance between people, but also change the traditional teaching mode. As the main force of the future economic market, the college students of economic management have strong dependence and interest on Internet technology. Colleges and universities should make full use of the learning interests and characteristics of students majoring in economics and management. In addition to cultivating students' economic mind and economic thinking, they should also cultivate students' comprehensive literacy from the point of view of creating people by virtue. Make it set up a good view of material and life values.

scholarly journals Progress of high temperature polybenzimidazole proton exchange membrane: a systematic review

2021 ◽  
Vol 2076 (1) ◽  
pp. 012032
Author(s):  
Guanghan Liu
Keyword(s):  
High Temperature ◽  
Fuel Cell ◽  
Proton Exchange Membrane ◽  
Strong Dependence ◽  
Water Environment ◽  
Oxidative Degradation ◽  
Proton Exchange ◽  
Point Of View ◽  
Exchange Membrane ◽  
High Temperature Pem

Abstract Proton exchange membrane (PEM) is the core component of proton fuel cell. Generally speaking, ordinary PEM has the poor barrier to fuel (especially liquid fuel) and proton conduction has a strong dependence on water molecules. Compared with ordinary PEM, high temperature fuel cell works in high temperature non-water environment, which overcomes the above problems. Besides, the system is complex with low impurity and much simpler flow field design. Polybenzimidazole (PBI) not only meets the requirements of high temperature, but also has higher proton conductivity than ordinary PEM, i.e., is the best material for high temperature PEM. From this point of view, the properties and fabrication of PBI are systematically reviewed. Specifically, the factors influencing the performance of acid doped PBI high temperature PEM as well as existing problems (high temperature degradation as well as chemical oxidative degradation) are demonstrated. Furthermore, the corresponding solutions and future direction are put forward.

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