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Статті в журналах з теми "Energies surface anisotropie":
1
Vidyasagar, A., S. Krödel, and D. M. Kochmann. "Microstructural patterns with tunable mechanical anisotropy obtained by simulating anisotropic spinodal decomposition." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 474, no. 2218 (October 2018): 20180535. http://dx.doi.org/10.1098/rspa.2018.0535.
Анотація:
The generation of mechanical metamaterials with tailored effective properties through carefully engineered microstructures requires avenues to predict optimal microstructural architectures. Phase separation in heterogeneous systems naturally produces complex microstructural patterns whose effective response depends on the underlying process of spinodal decomposition. During this process, anisotropy may arise due to advection, diffusive chemical gradients or crystallographic interface energy, leading to anisotropic patterns with strongly directional effective properties. We explore the link between anisotropic surface energies during spinodal decomposition, the resulting microstructures and, ultimately, the anisotropic elastic moduli of the resulting medium. We simulate the formation of anisotropic patterns within representative volume elements, using recently developed stabilized spectral techniques that circumvent further regularization, and present a powerful alternative to current numerical techniques. The interface morphology of representative phase-separated microstructures is shown to strongly depend on surface anisotropy. The effective elastic moduli of the thus-obtained porous media are identified by periodic homogenization, and directionality is demonstrated through elastic surfaces. Our approach not only improves upon numerical tools to simulate phase separation; it also offers an avenue to generate tailored microstructures with tunable resulting elastic anisotropy.
2
SCHMIDT, W. G., J. L. FATTEBERT, J. BERNHOLC, and F. BECHSTEDT. "SELF-ENERGY EFFECTS IN THE OPTICAL ANISOTROPY OF GaP(001)." Surface Review and Letters 06, no. 06 (December 1999): 1159–65. http://dx.doi.org/10.1142/s0218625x99001281.
Анотація:
We calculate the reflectance anisotropy for GaP(001)(2×4) surfaces using a real-space multigrid method and ab initio pseudopotentials. Our results obtained within DFT-LDA show good qualitative agreement with recent experiments. This holds in particular for the stoichiometric trends. A strong negative anisotropy at low photon energies is linked to the formation of Ga–Ga bonds along the [110] direction. There are discrepancies, however, with respect to the line shape and the energetic positions of characteristic peaks. Substantial improvement is achieved by using a numerically efficient GW approach with approximations for local-field effects and dynamical screening. We find that the spectral features related to transitions between surface perturbed bulk wave functions are more strongly affected by self-energy corrections than anisotropies directly linked to surface electronic states.
3
Kido, Eiji. "Current status of the TAx4 surface detectors." EPJ Web of Conferences 283 (2023): 06003. http://dx.doi.org/10.1051/epjconf/202328306003.
Анотація:
Telescope Array (TA) is the largest ultrahigh-energy cosmic-ray (UHECR) observatory in the northern hemisphere. It explores the origin of UHECRs using a surface detector (SD) array, covering approximately 700 km2, and a fluorescence detector (FD) stations viewing the skies above the array. TA has found evidence for a cluster of cosmic rays with energies greater than 57 EeV known as a HotSpot. Recently, TA has obtained additional evidence for an excess of cosmic rays with energies above 1019.4 eV and also found implications of spectrum anisotropy. An expanded SD array and FD stations called TAx4 experiment was designed to increase the data collection rate at the highest energies to confirm the anisotropies with more data. We have constructed and deployed more than half of the SDs for the TAx4 experiment and began stable data taking operations. We present TAx4 SD’s current status.
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HE, L., Y. W. LIU, W. J. TONG, J. G. LIN, and X. F. WANG. "SURFACE ENERGY ENGINEERING OF Cu SURFACE BY STRAIN: FIRST-PRINCIPLES CALCULATIONS." Surface Review and Letters 20, no. 06 (December 2013): 1350054. http://dx.doi.org/10.1142/s0218625x13500546.
Анотація:
Surface energies of strained Cu surfaces were studied systematically using first-principles methods. Results showed that the strain-stabilization of Cu surface was anisotropic and strongly related to the strain distribution. This strain-induced approach could be used as an effective way to engineer the surface energies of metals.
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Filimonov, Sergey N. "Ab Initio Calculations of Absolute Surface Energies of Clean and Hydrogen Covered 3C-SiC(001), (110) and (111) Surfaces." Materials Science Forum 821-823 (June 2015): 363–66. http://dx.doi.org/10.4028/www.scientific.net/msf.821-823.363.
Анотація:
The absolute surface energies of three major low index surfaces of cubic silicon carbide (3C-SiC) are determined by first-principles density functional theory calculations. Calculations show that among clean 3C-SiC surfaces the Si-terminated 3C-SiC(001)-(3x2) surface has the lowest energy. The second and third lowest energy surfaces are the Si-terminated 3C-SiC(111)-(√3x√3) surface and the nonreconstructed 3C-SiC(110) surface. Hydrogen passivation greatly reduces both the absolute surface energies of the low index 3C-SiC surfaces and the surface energy anisotropy. In particular, the surface energies of fully passivated 3C-SiC(110) and (111) surfaces become indistinguishable at hydrogen-rich deposition conditions.
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Семина, М. А., А. А. Головатенко, Т. В. Шубина та А. В. Родина. "Локализация носителей в квантовых точках с одноосной анизотропией формы и состава". Физика твердого тела 61, № 4 (2019): 636. http://dx.doi.org/10.21883/ftt.2019.04.47405.335.
Анотація:
AbstractThe electronic and hole states in quantum dots (QD) of cubic II–VI semiconductors with a spheroidal shape and uniaxial anisotropy have been studied theoretically. The smooth potential energy profiles simulated by the Gauss function in all three spatial directions are considered. The energy level lowering and the energy splitting of the hole state from the valence band top Γ_8 by momentum 3/2 into the states with projections ±3/2, ±1/2 on the anisotropy axis are analyzed. The QD anisotropies of three types are considered: the QD size anisotropy, the QD potential barrier anisotropy, and the combined anisotropy. In the first case, flattened quantum dots, in which the characteristic size in the structure plane is larger than the size along the anisotropy axis, are considered. In the second case, QDs, in which the potential barrier height in the plane is lower than that along the anisotropy axis, are considered. In the third case, flattened quantum dots with the anisotropy of the size and the potential barrier are considered. The conditions of the charge carrier localization inside QD have been found, and the influence of the form and composition anisotropies on the energies of exciton transitions in the structures with Cd_ x Zn_1 – _ x Se quantum dots are discussed.
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Palmer, Bennett. "Stable closed equilibria for anisotropic surface energies: Surfaces with edges." Journal of Geometric Mechanics 4, no. 1 (2012): 89–97. http://dx.doi.org/10.3934/jgm.2012.4.89.
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Suomijärvi, T. "The AugerPrime upgrade of the Pierre Auger Observatory." Journal of Physics: Conference Series 2429, no. 1 (February 1, 2023): 012010. http://dx.doi.org/10.1088/1742-6596/2429/1/012010.
Анотація:
Abstract Operating since 2004, the Pierre Auger Observatory has yielded several important results. The suppression of the flux around 5×1019 eV is now confirmed without any doubt, a large-scale dipole anisotropy has been found for energies above 8×1018 eV, as well as an indication for some intermediate-scale anisotropy at the highest energies. Furthermore, strong limits have been placed on ultra-high-energy photons and neutrinos. In order to elucidate the origin of the flux suppression at the highest energies and search for composition-enhanced anisotropies, the Auger Collaboration is currently upgrading the Observatory. In the framework of the upgrade, called AugerPrime, the array of 1660 water-Cherenkov detectors is equipped with plastic scintillators, allowing us to enhance the composition sensitivity. The station electronics is also upgraded, including better timing with up-to-date GPS receivers, higher sampling frequency, and increased dynamic range. Currently, more than 40% of the surface detectors have been upgraded, and the commissioning studies are well advanced. In this paper, the design of the AugerPrime surface detectors will be presented, and the performance obtained from the analysis of the first data will be discussed.
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Elsey, Matt, and Selim Esedoḡlu. "Threshold dynamics for anisotropic surface energies." Mathematics of Computation 87, no. 312 (October 19, 2017): 1721–56. http://dx.doi.org/10.1090/mcom/3268.
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Stinner, Björn. "Multi-phase field systems with anisotropic surface energies." PAMM 7, no. 1 (December 2007): 1150101–2. http://dx.doi.org/10.1002/pamm.200700476.
Дисертації з теми "Energies surface anisotropie":
1
Zhai, Xinyuan. "Crack propagation in elastic media with anisotropic fracture toughness : experiments and numerical modeling." Electronic Thesis or Diss., Institut polytechnique de Paris, 2023. http://www.theses.fr/2023IPPAE010.
Анотація:
La fabrication additive attire une attention croissante en raison de ses avantages en termes de flexibilité de modélisation et de facilité de conception de microstructures complexes. Nous avons constaté qu'en manipulant la stratégie d'impression, les échantillons imprimés par dépôt de fusion de polycarbonate peuvent présenter un comportement fortement anisotrope en termes de résistance à la rupture, tout en conservant des propriétés isotropes en termes d'élasticité.Le focus de cette thèse est d'explorer le comportement en matière de rupture dans des milieux élastiques isotropes présentant une ténacité de rupture anisotrope, en utilisant une combinaison d'investigations expérimentales et de simulations numériques. Dans la partie expérimentale, nous examinons la propagation des fissures dans diverses conditions de chargement en utilisant des géométries d'échantillons variées, englobant à la fois le Mode I et le Mode I+II. Dans la partie numérique, nous adoptons la modélisation de la fissuration fragile par champ de phase basée sur l'approche variationnelle, en utilisant des données expérimentales pour l'étalonnage et l'identification des paramètres numériques. À travers ces méthodologies complètes, notre objectif est de favoriser une compréhension plus profonde de l'interaction entre les motifs d'impression et la sélection des trajectoires de fissures. Cette compréhension a des implications significatives pour guider et gérer la propagation des fissures dans les composants fabriqués par fabrication additive. De plus, nous adoptons les critères classiques basés sur le taux de restitution d'énergie maximale généralisé pour améliorer notre compréhension de la sélection des trajectoires de fissures et de la force critique correspondante.Dans la dernière partie de cette thèse, nous présentons quelques investigations préliminaires concernant l'éventuelle émergence d'un motif de fissure en Zig-Zag dans des spécimens imprimés en 3D. De plus, nous plongeons en profondeur dans le comportement de rupture des spécimens imprimés sous chargement cyclique, offrant une comparaison exhaustive entre les observations expérimentales et les prévisions numériquesAdditive manufacturing is receiving increasing attention due to its advantages in terms of modelling flexibility and allowing to easily design complex micro-structures. Through the manipulation of the printing strategy, we observed that fused deposition of polycarbonate can result in printed samples showcasing a distinct anisotropic behavior in fracture toughness, all the while retaining isotropic properties in elasticity.This thesis is dedicated to investigating fracture behavior within isotropic elastic media with anisotropic fracture toughness. The approach involves a combination of fracture experiments and numerical simulations. In the experimental part, we examine crack propagation under various loading conditions using diverse sample geometries, encompassing both Mode I and Mode I+II loading condition. In the numerical part, we adopt the phase-field modeling of brittle fracture based on a variational approach, using experimental data for calibrating and identification of the numerical parameters. Through these comprehensive methodologies, our objective is to foster a deeper comprehension of the interplay between printing patterns and the selection of crack paths. This understanding holds significant implications for guiding and controlling crack propagation in additive manufacturing-produced components. Besides, we adopted the classical based criteria Generalized Maximum Energy Release Rate to enhance our understanding of crack path selection and the relevant critical force.In the last part of this thesis, we presents some preliminary investigations regarding the potential emergence of Zig-Zag crack patterns in 3D printed specimens. Additionally, we delve extensively into the fracture behavior of printed specimens under cyclic loading, offering a comprehensive comparison between experimental observations and numerical forecasts
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Mekhiche, Mouhoub. "Introduction de la texture cubique {100}<001> dans les dispositifs électrotechniques : de la métallurgie à la modélisation." Grenoble INPG, 1995. http://www.theses.fr/1995INPG0019.
Анотація:
La principale plage de progression des performances magnétiques des aciers magnétiques FeSi est à l'heure actuelle la texture de ces matériaux. Il est alors important de savoir évaluer l'intérêt de telle ou telle texture pour l'électrotechnique, afin de connaître les marges de progrès existant encore dans la conception de différents dispositifs et d'estimer par là même s'il est intéressant ou non de mettre au point métallurgiquement telle texture. Le travail présenté a pour ambition de mettre en place un tel outil intégré d'étude et d'évaluation d'une texture, relativement aux contraintes du génie électrique: dans ce but nous nous sommes appliqués à l'étude et l'évaluation de la texture "cubique" {100}<001>. La synthèse métallurgique de cette texture a été obtenue à partir d'un procédé associant laminage croisé, énergie de surface et aluminium. L'étude a naturellement montré que cette association permettait d'obtenir une forte texture {100} même avec de fortes vitesses de montée en température. Après un passage nécessaire par une caractérisation magnétique 2D, un modèle d'aimantation anisotrope et anhystérétique a été élaboré pour rendre compte du comportement magnétique des tôles texturées. Enfin l'introduction de matériaux texturés dans les dispositifs électrotechniques a été étudiée sur la baseCurrently, the principal range of improvement in the magnetic performances of SiFe magnetic steels is found in the texture of these materials. It is therefore important to know how to evaluate the interest of a given texture for use in electrical engineering in order to know the margines of progress still existing in the design of different devices, and also to estimate if it is interesting or not to metallurgically develop such a texture. The present work aims to set up a tool integrated to study and evaluate a texture, relative to the constraints of electrical engineering. Towards this goal we have focused on the study and evaluation of the "cubic" texture {100}<001>. The metallugic synthesis of this texture was obtained from a procedure which associates cross rolling, surface energy and aluminium. The study showed that this association obtained a strong {100} texture even with quick rises in temperature. After a necessary phase of 2D magnetic characterization, a model of anisotropic and non hysteretic magnetization was elaborated to find the magnetic behavior of textured sheets. Finally, the introduction of such textured materials into electrical devices was studied, based on electromagnetic modeling software well adapted to the description of anisotropy
3
Gottlieb, Ulrich. "Quelques propriétés physiques intrinsèques des siliciures métalliques et semiconducteurs." Grenoble INPG, 1994. http://www.theses.fr/1994INPG0008.
Анотація:
Dans la premiere partie nous decrivons la mise au point d'une experience de mesures de transport a basses temperatures. Nous avons construit un dispositif experimental qui permet de piloter la rotation de l'echantillon a basse temperature sous fort champ magnetique a partir de l'exterieur du cryostat. La deuxieme partie de la these est consacree a l'etude systematique des siliciures isostructuraux et isoelectroniques vsi#2, nbsi#2 et tasi#2. Les echantillons sont monocristallins. Les trois composes sont metalliques et leur resistivite a haute temperature est anisotrope. Des mesures de magnetoresistance nous ont permis d'explorer la surface de fermi de nbsi#2. Des mesures de chaleur specifique a tres basse temperature revelent que la densite d'etats electronique au niveau de fermi est deux fois plus elevee pour vsi#2 que pour les deux autres siliciures. Les temperatures de debye des trois composes varient en fonction de m##1#/#2 (m: masse molaire) indiquant que les forces interatomiques sont identiques. Nbsi#2 et tasi#2 sont supraconducteurs en dessous respectivement 130 mk et 353 mk. Des mesures de susceptibilite montrent que vsi#2 est paramagnetique, nbsi#2 et tasi#2 sont diamagnetiques. Les spectres de phonons obtenus par des mesures de spectroscopie de pointes sont en bon accord avec les temperatures de debye obtenues par les autres methodes. Des etudes sur les proprietes de transport des siliciures semiconducteurs crsi#2, resi#1#,#7#5 et ru#2si#3 sont decrites dans le troisieme chapitre. La preparation de monocristaux de ces materiaux est plus difficile que celle des siliciures metalliques. La resistivite des trois composes est anisotrope. Ru#2si#3 et resi#1#,#7#5 se comportent comme des semiconducteurs dopes en regime extrinseque. Crsi#2 montre plutot le comportement d'un mauvais metal. La magnetoresistance de ru#2si#3 a basse temperature peut s'interpreter dans un modele de localisation faible ou les interactions electron-electron sont dominantes
4
Favretto-Cristini, Nathalie. "Interaction ondes/interfaces en contexte sismique." Habilitation à diriger des recherches, Université de la Méditerranée - Aix-Marseille II, 2011. http://tel.archives-ouvertes.fr/tel-00598344.
Анотація:
Certains besoins économiques, sociétaux ou environnementaux nécessitent une caractérisation approfondie des structures géologiques du sous-sol. Parmi les différentes méthodes géophysiques, la sismique est sans doute celle qui est le plus souvent privilégiée. Imager et caractériser le sous-sol à partir de données réelles acquises sur le terrain est cependant un problème inverse généralement di fficile à résoudre. Il l'est d'autant plus si le problème direct associé n'a pas été au préalable "maîtrisé" a minima, c'est-à-dire si l'on ne dispose pas d'une modélisation réaliste de la propagation des ondes. Pour cela, il semble essentiel, pour modéliser les données sismiques synthétiques a fin de les rendre comparables aux données réelles, d'identi fier et de comprendre en premier lieu les facteurs géologiques et/ou physiques de premier ordre qui in fluencent la propagation des ondes dans une con figuration donnée. Cela suppose qu'on prenne en compte à la fois les lois de comportement des couches géologiques traversées et les lois de contact entre ces couches, mais aussi les limitations introduites par le système d'observation constitué par les ondes sismiques. Ce mémoire décrit les travaux que j'ai menés essentiellement sur la compréhension et la modélisation de l'interaction ondes/interfaces en me basant sur des approches pluridisciplinaires. Outre l'aspect fondamental d'une meilleure connaissance des mécanismes physiques sous-jacents à la propagation des ondes dans des milieux complexes (e.g., les résolutions sismiques verticale et latérale, la dé finition du ré flecteur sismique 3D, la diffusion d'interface et l'in fluence de l'anisotropie sur les ondes de surface), des aspects plus appliqués, dédiés notamment à l'exploration de gisements énergétiques ou à la surveillance de réservoirs géologiques de stockage du CO2, ont été également développés.
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Liscio, Fabiola. "Nanostructures magnetiques auto-assemblees sur des surfaces a faible energie par epitaxie par jets moleculaires." Phd thesis, 2009. http://tel.archives-ouvertes.fr/tel-00391031.
Анотація:
Les nanostructures d'alliages MxPt1x (M=Co et Fe) developpent des anisotropies magnetiques perpendiculaires, très interessantes pour des applications dans le domaine de l'enregistrement a haute densite. Dans ce travail de these, la nature du substrat (structure, symetrie et energie de surface) et l'in uence de la temperature de co-deposition sur les proprietes structurales et magnetiques des nanostructures ont ete etudies. La methode a consiste a deposer des atomes de metaux de transition par epitaxie a jets moleculaires sur les surfaces WSe2(001) et NaCl(001) de faible energie. Elle a conduit a la formation de nanostructures modeles, non contraintes dont les proprietes ont ete determinees par differentes techniques (diffraction X, XAFS, GISAXS, MET, STM et magnetometrie SQUID). Les effets de mise en ordre chimique a courte et a longue distance et l'infl uence de la morphologie et de la direction de croissance sur les proprietes magnetiques ont ete clairement demontres.
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Baer, Eric Theles. "Symmetry properties of crystals and new bounds from below on the temperature in compressible fluid dynamics." Thesis, 2012. http://hdl.handle.net/2152/ETD-UT-2012-08-5999.
Анотація:
In this thesis we collect the study of two problems in the Calculus of Variations and Partial Differential Equations. Our first group of results concern the analysis of minimizers in a variational model describing the shape of liquid drops and crystals under the influence of gravity, resting on a horizontal surface. Making use of anisotropic symmetrization techniques and an analysis of fine properties of minimizers within the class of sets of finite perimeter, we establish existence, convexity and symmetry of minimizers. In the case of smooth surface tensions, we obtain uniqueness of minimizers via an ODE characterization. In the second group of results discussed in this thesis, which is joint work with A. Vasseur, we treat a problem in compressible fluid dynamics, establishing a uniform bound from below on the temperature for a variant of the compressible Navier-Stokes-Fourier system under suitable hypotheses. This system of equations forms a mathematical model of the motion of a compressible fluid subject to heat conduction. Building upon the work of (Mellet, Vasseur 2009), we identify a class of weak solutions satisfying a localized form of the entropy inequality (adapted to measure the set where the temperature becomes small) and use a form of the De Giorgi argument for L[superscript infinity] bounds of solutions to elliptic equations with bounded measurable coefficients.text
Частини книг з теми "Energies surface anisotropie":
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Handa, S. "Technology of reactive ion etching." In Plasma Etching Fundamentals and Applications, 180–211. Oxford University PressOxford, 1998. http://dx.doi.org/10.1093/oso/9780198562870.003.0005.
Анотація:
Abstract The original meaning of ‘etching’ is ‘to eat’; the process of removing something from an object. Moreover, it is impressive that another original meaning of it is ‘to feed’. In fact, reactive ion etching (RIE) consists of two processes; ‘to eat’ and ‘to feed’. The physical process of etching is to remove particles from a solid surface by the colliding energy of ions which is converted into thermal, chemical, or kinetic energy. The mechanisms of etching can be classified by forms of energy exchange: chemical and physical. The etched pattern can be classified into two types: anisotropic (directional) etching and isotropic (indirectional) etching. When thermal and chemical energies are transformed in the reaction, then indirectional etching will be processed. Liquid chemical etching is a typical example of indirectional etching.
2
Coker, D. F., and R. O. Watts. "Diffusion Monte Carlo simulation of condensed systems." In Quantum Monte Carlo, 48. Oxford University PressNew York, NY, 2007. http://dx.doi.org/10.1093/oso/9780195310108.003.0051.
Анотація:
Abstract This paper reports diffusion quantum Monte Carlo calculations for condensed systems, in this case for liquid 4He and for solid molecular H2. Calculations for liquid He made earlier by Whitlock et al.a using Green’s function QMC for the same potential energy surface allowed a comparison of results for this system. Coker and Watts used spherical pair potentials derived from scattering experiments for both systems, along with Axilrod-Teller-Muto three body terms. The calculations were performed with importance sampling, using a simple product of pair functions as a trial function for helium. For hydrogen a simple pair function multiplied by a single-particle term for position in the fee lattice was used. Periodic boundary conditions were employed, and calculations were carried out for several particle densities of each species. For helium, good agreement with the prior Green’s function calculations was obtained for thermodynamic and structural properties and for radial distribution functions. For hydrogen, the calculated average energies and pressures gave general agreement with experimental measurement, but they differed up to 10% in energy and 12% in pressure in a manner to be expected for neglect of molecular anisotropy. The problem treated in this paper is that of understanding xenon cluster ions at the microscopic level. Some properties of cluster anions had been measured, but these revealed no detailed information on structure and energetics. In the study reported here, diffusion QMC was used to investigate electron binding to small clusters of up to 19 atoms in fixed minimum-energy configurations. This was followed by path integral calculations to determine equilibrium distributions of cluster structures at temperatures of 10-100 K for several cluster sizes.
Тези доповідей конференцій з теми "Energies surface anisotropie":
1
Bucklen, B., M. Wettergreen, M. Heinkenschloss, and M. A. K. Liebschner. "Surface-Based Scaffold Design: A Mechanobiological Approach." In ASME 2005 International Mechanical Engineering Congress and Exposition. ASMEDC, 2005. http://dx.doi.org/10.1115/imece2005-81985.
Анотація:
Despite recent need-based advances in orthopedic scaffold design, current implants are unsuitable as “total” scaffold replacements. Both mechanical requirements of stiffness/strength and biological stipulations dictating cellular behavior (attachment, differentiation) should be included. The amount of mechanical stimulation in the form of stresses, strains, and energies most suitable toward implant design is presently unknown. Additionally unknown is if whole-bone optimization goals such as uniform and non-uniform driving forces are applicable to a scaffold-bone interface. At the very least, scaffolds ready for implantation should exhibit mechanical distributions (dependent on loading type) on the surface within the typical mechanical usage window. Scaffold micro-architectures can be strategically shifted into that window. The overall goal of this study was to produce microarchitectures tailored to a more uniform mechanical distribution, while maintaining the morphological properties necessary to sustain its mechanical integrity. The mechanical adjustment stimuli investigated were von Mises stress, strain energy density, maximum principle strain, and volumetric strain. Scaffold models of a similar volume fraction were generated of three initial architectures (Rhombitruncated Cuboctahedron, hollow sphere, and trabecular-like bone cube) using high resolution voxel mapping. The resulting voxels were translated into finite element meshes and solved, with a specially written iterative solver created in Fortran90, under confined displacement boundary conditions. The result was verified against a commercial software. Once the mechanical distributions were identified one of two methods was chosen to alter the configuration of material in Cartesian space. The success of the alteration was judged through a diagnostic based on the histogram of mechanical values present on the surface of the micro-architecture. The first method used a compliant approach and, for the case of stress, reinforced locations on the surface with large stresses with extra material (strategically taken from the least stressed portions). The second method used a simulated annealing approach to randomly mutate the initial state in a “temperature” dependent manner. Results indicate that the mechanical distributions of the initial scaffold designs vary significantly. Additionally, the end state of the adjustment demonstrated anisotropy shifts toward the direction of loading. Moreover, the adjustment methods were found to be sensitive both to the mechanical parameter used for adjustment and the portion of the surface adjusted at each increment. In conclusion, scaffolds may be adjusted using a mechanical surface-based objective, as the surface of the scaffold is crucial toward its in vivo acceptance. This technique provides some mathematical specificity toward the whole of computer-aided tissue engineering.
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Zhao, Xinglong, Joa˜o Quinta da Fonseca, Andrew Sherry, and David Lidbury. "Grain-Scale Heterogeneity Effect on Mechanistic Modelling of Cleavage Fracture of a Ferritic RPV Steel Forging Material." In ASME 2008 Pressure Vessels and Piping Conference. ASMEDC, 2008. http://dx.doi.org/10.1115/pvp2008-61569.
Анотація:
Improving brittle fracture prediction is crucial for structural integrity assessment. In current safety assessments, fracture mechanics treats polycrystalline steels as homogeneous continua. In reality, deformation of structural steels is heterogeneous. Part of this heterogeneity is due to the elastic and plastic anisotropy of their constituent (often randomly orientated) grains. This paper will compare the predicted failure stresses from tensile tests performed on a ferritic pressure vessel steel using the crystal plasticity finite element approach alongside measured carbide distribution and classical Beremin cleavage model. Available tensile data of 22NiMoCr37 steel at low temperature (−91°C and −154°C) were analysed using Bridgman solutions to account for the necking effect on the stress state at the centre of necking where brittle cracking initiates. This stress state imposed on representative volume element (RVE) made up of 10×10×10 randomly orientated grains, whose deformation is simulated using crystal plasticity finite element modelling (CPFEM). Randomly distributed carbides were produced based on the measured carbide size distribution and density for this steel. By assuming carbides as Griffith microcracks, the cleavage fracture stress in each grain can be assessed based the maximum principal stress on the cleavage crystal plane and an assumed surface energy. By repeating the random carbide distribution 1,000 times, brittle fracture probability can be calculated. Detailed examination shows that the above approach is actually a verification of the BEREMIN local approach model for cleavage fracture. The modelling results were compared with the available ductility data at −91°C and the interpolated ductility data at −154°C at the centre of necking. It is foreseen that this approach will lead to improvements in brittle fracture modelling in heterogeneous ferritic steels by introducing realistic surface energies and real defect distributions in specific materials, when used alongside the CPFEM submodelling approach.