Local Deformation Behavior of the Copper Harmonic Structure near Grain Boundaries Investigated through Nanoindentation

The copper harmonic structure, which consists of a coarse-grained “core” surrounded by a three-dimensional continuously connected fine-grained “shell,” exhibits both high ductility and high strength. In the present study, dislocation interactions at the shell–core boundary in the copper harmonic structure were directly measured using nanoindentation and microstructural observations via kernel average misorientation (KAM) to further understand the reason for its excellent mechanical properties. KAM analysis showed that the dislocation density in the vicinity of the shell–core boundary within the core region gradually increases with increasing plastic strain. The variation in the nanohardness exactly corresponds to the KAM, indicating that the higher strength is primarily caused by the higher dislocation density. The critical load for nanoindentation-induced plasticity initiation was lower at the shell–core boundary than at the core–core boundary, indicating a higher potency of dislocation emission at the shell–core boundary. Because dislocation–dislocation interactions are one of the major causes of the increase in the flow stress leading to higher strain hardening rates during deformation, the excellent balance between strength and ductility is attributed to the higher potency of dislocation emission at the shell–core boundary.

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Harmonic Structure Design of Co-Cr-Mo Alloy with Outstanding Mechanical Properties

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.939.60 ◽

2014 ◽

Vol 939 ◽

pp. 60-67 ◽

Cited By ~ 3

Author(s):

Choncharoen Sawangrat ◽

Osamu Yamaguchi ◽

Sanjay Kumar Vajpai ◽

Kei Ameyama

Keyword(s):

Mechanical Properties ◽

Mechanical Milling ◽

Three Dimensional ◽

High Strength ◽

Surface Region ◽

Structure Design ◽

Coarse Grained ◽

Harmonic Structure ◽

Fine Grained ◽

Plasma Sintering

Co-Cr-Mo alloy powders were subjected to controlled mechanical milling at room temperature under Ar atmosphere to fabricate bimodal microstructure in the MM powders, having nanosized grains in the surface region and micron-sized coarse grains in the center of the milled powders. Subsequently, the MM powder was compacted by spark-plasma sintering (SPS) process. The sintered compacts indicated two structure areas: (i) ultra-fine grained (UFG) regions, called shell, and (ii) the coarse grained regions called core. The shell and the core correspond to the surface and center of the MM powders, respectively. The shell regions established a continuous three dimensional network of high strength ultra-fine grained regions, which surrounded the discrete coarse grained ductile regions. Such a microstructure is referred as Harmonic Structure. The sintered Co-Cr-Mo alloy compacts exhibited outstanding mechanical properties. The yield strength increased from 605 to 635 MPa, and ultimate tensile strength increased from 1201 to 1283 MPa. Moreover, the elongation was maintained more or less same as that of coarse grained compacts. Therefore, the harmonic structure design leads to the new generation microstructure of Co-Cr-Mo alloy, which demonstrates outstanding mechanical properties, i.e. superior strength and excellent ductility as compared to conventional materials. Keywords: mechanical milling, Co-Cr-Mo alloys, mechanical properties, harmonic structure.

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Deformation Behavior Analysis of Harmonic Structure Materials by Multi-Scale Finite Element Analysis

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.1088.853 ◽

2015 ◽

Vol 1088 ◽

pp. 853-857 ◽

Cited By ~ 16

Author(s):

Han Yu ◽

Ikumu Watanabe ◽

Kei Ameyama

Keyword(s):

Finite Element Analysis ◽

Finite Element ◽

Three Dimensional ◽

Model Material ◽

Structure Design ◽

Coarse Grained ◽

Harmonic Structure ◽

Element Analysis ◽

Multi Scale ◽

Microscopic Deformation

The harmonic structure materials consist of coarse-grained areas enclosed in a three-dimensional continuously connected network of ultrafine-grained area. The concept of harmonic structure design has been successfully applied to a variety of pure metals and alloys by mechanical milling (MM) and subsequent powder metallurgy (PM) process. In harmonic structure material, core region with coarse grains maintains a high ductility while the shell region with ultrafine grains contributes for a higher strength. Therefore, the material with harmonic structure design can achieve both strength and ductility simultaneously. In this research, the SUS304L grade stainless steel has been used as a model material to understand and validate the response of the harmonic structure materials towards the applied external loads. The numerical simulation of multi-scale FEA (Finite Element Analysis) was carried out, and it was confirmed that microscopic deformation and the macroscopic tensile strength can be characterized by the present approach.

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Novel Honeycomb Glassfiber Mat as the Core of Vacuum Insulation Panel

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.900.247 ◽

2014 ◽

Vol 900 ◽

pp. 247-250

Author(s):

Cheng Dong Li ◽

Zhao Feng Chen

Keyword(s):

Thermal Insulation ◽

High Performance ◽

Three Dimensional ◽

High Strength ◽

Glass Wool ◽

Core Material ◽

The Core ◽

Vacuum Insulation ◽

Novel Structure ◽

Chopped Strand Mat

Vacuum insulation panels (VIPs) are regarded as one of the most promising high-performance thermal insulation solutions on the market today. In this paper, a novel structure, i.e., honeycomb glassfiber mat was proposed as the core material of VIP. The honeycomb glassfiber mat was composed of glass wool mat and glassfiber chopped strand mat. Among them, 70% centrifugal glass wool and 30% flame attenuated glass wool were mixed together to form the 0.5mm-thickness glass wool mat, while thirteen holes with diameter of 10mm were opened uniformly on the surface of glassfiber chopped strand mat. Glassfiber VIPs possessed honeycomb core material have superior thermal conductivity of 1.52mW/(m•K). In order to obtain better thermal insulation performance, ultrafine and stiff fibers with three-dimensional overlapping structure is preferable. Meanwhile, hollow fibers with bifurcated structure are the guarantee of high-strength core material.

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Observations of dislocation interactions with recrystallized grain boundaries

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100105205 ◽

1988 ◽

Vol 46 ◽

pp. 628-629

Author(s):

C. W. Price

Keyword(s):

Dislocation Density ◽

Grain Boundary ◽

Strain Rate ◽

Grain Boundaries ◽

Dislocation Structure ◽

Hot Deformation ◽

Static Recrystallization ◽

High Dislocation Density ◽

High Angle ◽

Dislocation Interactions

Little evidence exists on the interaction of individual dislocations with recrystallized grain boundaries, primarily because of the severely overlapping contrast of the high dislocation density usually present during recrystallization. Interesting evidence of such interaction, Fig. 1, was discovered during examination of some old work on the hot deformation of Al-4.64 Cu. The specimen was deformed in a programmable thermomechanical instrument at 527 C and a strain rate of 25 cm/cm/s to a strain of 0.7. Static recrystallization occurred during a post anneal of 23 s also at 527 C. The figure shows evidence of dissociation of a subboundary at an intersection with a recrystallized high-angle grain boundary. At least one set of dislocations appears to be out of contrast in Fig. 1, and a grainboundary precipitate also is visible. Unfortunately, only subgrain sizes were of interest at the time the micrograph was recorded, and no attempt was made to analyze the dislocation structure.

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Compressive behaviours of octet-truss lattices

Proceedings of the Institution of Mechanical Engineers Part C Journal of Mechanical Engineering Science ◽

10.1177/0954406220913586 ◽

2020 ◽

Vol 234 (16) ◽

pp. 3257-3269 ◽

Cited By ~ 1

Author(s):

Yifan Li ◽

Huaiyuan Gu ◽

Martyn Pavier ◽

Harry Coules

Keyword(s):

Failure Modes ◽

Density Ratio ◽

Three Dimensional ◽

Compressive Load ◽

High Strength ◽

Detailed Comparison ◽

Compressive Response ◽

Beam Elements ◽

Structural Applications ◽

Octet Truss

Octet-truss lattice structures can be used for lightweight structural applications due to their high strength-to-density ratio. In this research, octet-truss lattice specimens were fabricated by stereolithography additive manufacturing with a photopolymer resin. The mechanical properties of this structure have been examined in three orthogonal orientations under the compressive load. Detailed comparison and description were carried out on deformation mechanisms and failure modes in different lattice orientations. Finite element models using both beam elements and three-dimensional solid elements were used to simulate the compressive response of this structure. Both the load reaction and collapse modes obtained in simulations were compared with test results. Our results indicate that three-dimensional continuum element models are required to accurately capture the behaviour of real trusses, taking into account the effects of finite-sized beams and joints.

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Solubilization of Charged Porphyrins in Interpolyelectrolyte Complexes: A Computer Study

Polymers ◽

10.3390/polym13040502 ◽

2021 ◽

Vol 13 (4) ◽

pp. 502

Author(s):

Karel Šindelka ◽

Zuzana Limpouchová ◽

Karel Procházka

Keyword(s):

Dissipative Particle Dynamics ◽

Water Soluble ◽

Coarse Grained ◽

Core Shell ◽

Computer Study ◽

Interpolyelectrolyte Complex ◽

The Core ◽

Porphyrin Derivatives ◽

Oppositely Charged ◽

Positively Charged

Using coarse-grained dissipative particle dynamics (DPD) with explicit electrostatics, we performed (i) an extensive series of simulations of the electrostatic co-assembly of asymmetric oppositely charged copolymers composed of one (either positively or negatively charged) polyelectrolyte (PE) block A and one water-soluble block B and (ii) studied the solubilization of positively charged porphyrin derivatives (P+) in the interpolyelectrolyte complex (IPEC) cores of co-assembled nanoparticles. We studied the stoichiometric mixtures of 137 A10+B25 and 137 A10−B25 chains with moderately hydrophobic A blocks (DPD interaction parameter aAS=35) and hydrophilic B blocks (aBS=25) with 10 to 120 P+ added (aPS=39). The P+ interactions with other components were set to match literature information on their limited solubility and aggregation behavior. The study shows that the moderately soluble P+ molecules easily solubilize in IPEC cores, where they partly replace PE+ and electrostatically crosslink PE− blocks. As the large P+ rings are apt to aggregate, P+ molecules aggregate in IPEC cores. The aggregation, which starts at very low loadings, is promoted by increasing the number of P+ in the mixture. The positively charged copolymers repelled from the central part of IPEC core partially concentrate at the core-shell interface and partially escape into bulk solvent depending on the amount of P+ in the mixture and on their association number, AS. If AS is lower than the ensemble average ⟨AS⟩n, the copolymer chains released from IPEC preferentially concentrate at the core-shell interface, thus increasing AS, which approaches ⟨AS⟩n. If AS>⟨AS⟩n, they escape into the bulk solvent.

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Internal Force on and Deformation of Steel Assembled Supporting Structure of Foundation Pit under Thermal Stress

Applied Sciences ◽

10.3390/app11052225 ◽

2021 ◽

Vol 11 (5) ◽

pp. 2225

Author(s):

Fu Wang ◽

Guijun Shi ◽

Wenbo Zhai ◽

Bin Li ◽

Chao Zhang ◽

...

Keyword(s):

Three Dimensional ◽

Bending Moment ◽

High Strength ◽

Element Model ◽

Internal Force ◽

Foundation Pit ◽

Dimensional Finite Element ◽

Influence Of Temperature On ◽

Scale Experiment ◽

Three Dimensional Finite Element

The steel assembled support structure of a foundation pit can be assembled easily with high strength and recycling value. Steel’s performance is significantly affected by the surrounding temperature due to its temperature sensitivity. Here, a full-scale experiment was conducted to study the influence of temperature on the internal force and deformation of supporting structures, and a three-dimensional finite element model was established for comparative analysis. The test results showed that under the temperature effect, the deformation of the central retaining pile was composed of rigid rotation and flexural deformation, while the adjacent pile of central retaining pile only experienced flexural deformation. The stress on the retaining pile crown changed little, while more stress accumulated at the bottom. Compared with the crown beam and waist beam 2, the stress on waist beam 1 was significantly affected by the temperature and increased by about 0.70 MPa/°C. Meanwhile, the stress of the rigid panel was greatly affected by the temperature, increasing 78% and 82% when the temperature increased by 15 °C on rigid panel 1 and rigid panel 2, respectively. The comparative simulation results indicated that the bending moment and shear strength of pile 1 were markedly affected by the temperature, but pile 2 and pile 3 were basically stable. Lastly, as the temperature varied, waist beam 2 had the largest change in the deflection, followed by waist beam 1; the crown beam experienced the smallest change in the deflection.

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A Randomized Parallel Three-Dimensional Convex Hull Algorithm for Coarse-Grained Multicomputers

Theory of Computing Systems ◽

10.1007/s002240000067 ◽

1997 ◽

Vol 30 (6) ◽

pp. 547-558 ◽

Cited By ~ 7

Author(s):

F. Dehne ◽

X. Deng ◽

P. Dymond ◽

A. Fabri ◽

A. A. Khokhar

Keyword(s):

Convex Hull ◽

Three Dimensional ◽

Coarse Grained ◽

Convex Hull Algorithm

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On the formation and stability of fermionic dark matter halos in a cosmological framework

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3986 ◽

2020 ◽

Author(s):

Carlos R Argüelles ◽

Manuel I Díaz ◽

Andreas Krut ◽

Rafael Yunis

Keyword(s):

Black Hole ◽

Dark Matter ◽

Space Distribution ◽

Coarse Grained ◽

Dark Matter Halos ◽

The Core ◽

The Galaxy ◽

Gravitating Systems ◽

The Given ◽

First Time

Abstract The formation and stability of collisionless self-gravitating systems is a long standing problem, which dates back to the work of D. Lynden-Bell on violent relaxation, and extends to the issue of virialization of dark matter (DM) halos. An important prediction of such a relaxation process is that spherical equilibrium states can be described by a Fermi-Dirac phase-space distribution, when the extremization of a coarse-grained entropy is reached. In the case of DM fermions, the most general solution develops a degenerate compact core surrounded by a diluted halo. As shown recently, the latter is able to explain the galaxy rotation curves while the DM core can mimic the central black hole. A yet open problem is whether this kind of astrophysical core-halo configurations can form at all, and if they remain stable within cosmological timescales. We assess these issues by performing a thermodynamic stability analysis in the microcanonical ensemble for solutions with given particle number at halo virialization in a cosmological framework. For the first time we demonstrate that the above core-halo DM profiles are stable (i.e. maxima of entropy) and extremely long lived. We find the existence of a critical point at the onset of instability of the core-halo solutions, where the fermion-core collapses towards a supermassive black hole. For particle masses in the keV range, the core-collapse can only occur for Mvir ≳ E9M⊙ starting at zvir ≈ 10 in the given cosmological framework. Our results prove that DM halos with a core-halo morphology are a very plausible outcome within nonlinear stages of structure formation.

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