Self-consistent scale transition

Top PDF Self-consistent scale transition:

On the validity of the self-consistent scale transition model for inclusions with varying morphologies

On the validity of the self-consistent scale transition model for inclusions with varying morphologies

Eshelby’s solution-based homogenization procedures are often formulated from both Hill’s averages relations, equating the set average achieved over the mechanical strains (respectively stresses) of every inclusion constitut- ing the effective medium to the corresponding macro- scopic quantity (see relations (3) and (4) below). One can show that, when both of them are satisfied, the model is self-consistent, i.e., leads to the same macroscopic effective properties regardless of the equation used. Benveniste (1987) and several authors shown evidence that both Hill’s average relation could simultaneously be fulfilled by the Mori-Tanaka and self-consistent models, but at the cost of some restrictions over the materials microstructure: (i) either the inclusions must have the same Base Volume (BVs), i.e., shape and alignment of the elementary single heterogeneous inclusions accounted for achieving the scale-transition process should be strictly identical, (ii) or the material and inclusions must be isotropic, (iii) or only single or two-phase materials can be reliably modeled. This includes randomly oriented spheroidal particles, pen- ny-shaped particles randomly oriented in a layout, aligned fibers in a composite ply, isotropic aggregates... Analytic expressions of the thermo-elastic macroscopic properties of the effective medium have been elegantly determined for these cases in a series of paper from Benveniste, Dvo- rak, and Chen (1991, 1992) . Some applications also can be found in Pham (2000) or Qiu and Weng (1991) .
En savoir plus

10 En savoir plus

Localized necking predictions based on rate-independent self-consistent polycrystal plasticity: Bifurcation analysis versus imperfection approach

Localized necking predictions based on rate-independent self-consistent polycrystal plasticity: Bifurcation analysis versus imperfection approach

Marciniak and Kuczynski (1967) developed an approach based on the existence of an initial imperfection and coupled this localization criterion with an isotropic rigid-plastic constitutive framework in order to determine the right-hand side of the FLD. In most of the works devoted to the numerical prediction of FLDs, it is observed that both the shape and the location of these diagrams are extremely sensitive to the mechanical and physical properties. Accordingly, a wide range of phenome- nological behavior models have been coupled with various localization criteria to assess the in fluence of some constitutive features, such as for instance strain-rate sensitivity ( Khan and Baig, 2011 ), plastic anisotropy ( Zhang and Wang, 2012 ), and damage-induced softening ( Haddag et al., 2009; Abed-Meraim et al., 2014; Mansouri et al., 2014 ). Despite their good pre- dictive capabilities, the phenomenological models, which are the most widely used for the prediction of FLDs, are not able to account for some essential physical and mechanical features, such as initial and induced textures and other microstructure- related parameters (grain morphology, crystallographic structure …). These limitations represent the main motivations behind the more recent use of micromechanical modeling for the FLD prediction. The advantage of such physically-based modeling, compared to phenomenological approaches, is its ability to link, in a natural way, the material microstructure to some important in-use properties (strength, formability …). Indeed, in micromechanical modeling, the constitutive relations are expressed at the single crystal level, and account for mechanisms relevant at this scale in the description of the hardening, such as the slip of crystallographic planes, lattice rotation, dislocation motion … The constitutive relations of the poly- crystalline aggregate are derived from those of its components (i.e., single crystals) on the basis of some scale-transition schemes. Therefore, prediction of FLDs based on micromechanical modeling requires three main ingredients: constitutive modeling at the scale of the single crystal, a multi-scale scheme to determine the mechanical behavior of the polycrystalline material, and a localization approach to predict the initiation of strain localization.
En savoir plus

35 En savoir plus

Self-consistent cross-field transport model for core and edge plasma transport

Self-consistent cross-field transport model for core and edge plasma transport

a robust result, the change in V must therefore be associated to a change in the characteristic time, the latter then appearing as a key issue in under- standing and modeling turbulent transport. Finally the 1D model has been used to illustrate one of the possible problems that can be addressed in the κ-ε framework. Introducing in the definition of the velocity V a dependence on the shear of large scale flows, typically the zonal flows [44], so that the V exhibits a monotonic decrease from the low shear limit to the large shear limit, the ratio between these values being ≈ √ 2, we have reported in 1D simulations an H-mode like transition when increasing the input power, gen- erating an increased stored energy thanks to an interface barrier located at the separatrix [47]. This result is not quite a surprise since the predator-prey models have been introduced in fusion plasmas to investigate such barrier formation [41, 81, 46, 42]. Furthermore, the model has been devised to ex- hibit the appropriate trend, namely a decrease V with flow shear. However, the bifurcation aspect is not introduced specifically in the model. The tran- sition thus appears via a monotonic dependence of V on the shear completed by a feedback mechanism which governs a further increase of the flow shear as transport is reduced. This shows that the κ-ε model has the capability to generate changes of the transport regimes in a self-consistent manner.
En savoir plus

86 En savoir plus

Localized necking predictions based on rate-independent self-consistent polycrystal plasticity: Bifurcation analysis versus imperfection approach

Localized necking predictions based on rate-independent self-consistent polycrystal plasticity: Bifurcation analysis versus imperfection approach

materials. In their work, a two-dimensional formulation has been adopted (i.e., the localization band is assumed to lie in the plane of the sheet). The same type of approach is followed in the current contribution, except that the self-consistent multi- scale model is used instead of the Taylor model. The motivation behind this choice of a two-dimensional formulation for the bifurcation criterion is to allow comparisons between the predicted FLDs and those yielded by the initial imperfection approach (which usually follows a two-dimensional formulation). Besides the development of very powerful and ef ficient numerical tools for the prediction of ductility limits (which is, from the authors ’ perspective, an important originality in the current paper), we have also demonstrated another original result: when the initial imperfection ratio involved in the initial imperfection analysis tends towards zero, the associated FLDs tend towards the bifurcation-based FLD. It is noteworthy that this important result, which has already been demonstrated for phenomenological constitutive models (see, e.g., Ben Bettaieb and Abed-Meraim, 2015 ), is shown here to be valid for both scale-transition schemes, namely the Taylor model and the self- consistent scheme. Of course, such a comparison between the predictions given by the bifurcation theory and those yielded by the M eK analysis is not possible when the mechanical behavior is taken to be rate-dependent.
En savoir plus

35 En savoir plus

Eshelby-Kröner viscoelastic self-consistent model: Multi-scale behavior of polymer composites under creep loading

Eshelby-Kröner viscoelastic self-consistent model: Multi-scale behavior of polymer composites under creep loading

1 Introduction The thermal aging of polymers is a slow process occurring mainly on structural elements designed to experience mechanical loading, while being subjected to high temperatures for long periods. In many cases, matrix creep can occur. As the role of the matrices is essentially to deform and support stresses primarily in shear, it becomes then important to consider this particularity within a phenomenological modeling framework [4]. This context corresponds to the case of graphite- polyimide composites used in aerospace applications [1, 5]. According to, for instance, references [6, 7], below the glass transition temperature of its polymer matrix, composite materials exhibit a linear or at least a weakly nonlinear mechanical behavior until the damage threshold is attained. However, it is not the case anymore at high temperatures (relative to the glass transition temperature of the matrix). Indeed, recent experimental investigations performed at high temperatures on polyimide matrix composites, have shown very strong discrepancies from the linear elastic behavior [1, 2, 8]. These nonlinearities can be explained by two main mechanisms coupled together: the visco-elastic behviour of the polyimide matrix subjected to long-term loading at high temperatures, on the one hand, and the effects related to thermal aging, on the other hand.
En savoir plus

9 En savoir plus

Prediction of intergranular strains using a modified self-consistent elastoplastic approach

Prediction of intergranular strains using a modified self-consistent elastoplastic approach

GeM, Institut de Recherche en Génie Civil et Mécanique, UMR CNRS 8163, Université de Nantes, Ecole Centrales de Nantes, CRTT, 37 Boulevard de l’Université, BP 406, 44602 Saint-Nazaire cedex, France 1 Introduction Metal forming processes require knowledge of the evolution of the anisotropic elasto-plastic behaviour of the material during the deformation. Actually, the scale transition approach based on homogenisation techniques is currently used to predict the mechanical be- haviour of metallic materials at the macro- and micro- scopic levels [1, 2].

4 En savoir plus

Fully self-consistent multiparticle-multihole configuration mixing method : applications to a few light nuclei

Fully self-consistent multiparticle-multihole configuration mixing method : applications to a few light nuclei

correlation content of the nuclear state. In this way, the mp-mh method allows to treat on the same footing long range correlations, beyond a mean-field that is improved as correlations are introduced. First multiconfiguration-type calculations based on Hartree-Fock single-particle states (as opposed to the usual oscillator sates) have been realized in e.g. [ 85 , 91 , 18 , 76 , 61 ]. The orbitals were however kept frozen. Pioneering work using the full Multi-Configuration Self-Consistent Field approach in the context of nuclear physics has been done a few decades ago [ 34 , 39 , 96 , 60 ]. However the applications performed in these studies were restricted to simple analytical cases (Lipkin model). The development of the multiparticle-multihole con- figuration mixing method at CEA,DAM,DIF started in the early 2000’s. So far, the studies that have been performed have not applied the full self-consistent formalism. Recent analysis of the spectroscopy of sd-shell nuclei using the Gogny interaction [ 86 , 63 ] used frozen Hartree- Fock orbitals, while an earlier work [ 84 ] applied the mp-mh method to the description of pairing correlations in Sn isotopes making drastic approximations in the equation determining the single-particle states. The goal of this thesis is to pursue the development of the mp-mh approach to be able to apply the full formalism to the description of nuclei. After formal and numerical developments, we are now able to exercise for the first time the completely self-consistent method to a few light nuclei. In particular, the first applications of this work are done for p and sd-shell nuclei using the Gogny interaction.
En savoir plus

175 En savoir plus

Self-consistent modelling of heating synergy between NBI and ICRH in JET deuterium plasmas

Self-consistent modelling of heating synergy between NBI and ICRH in JET deuterium plasmas

permeability of vacuum, ~ j ext is current density of antenna, f i is distribution of resonant ion, C (f i ) is collision operator and Q  f i , ~ E  is the quasi-linear operator of wave/particle interaction. To have a complete modelling, it is needed to take account feedback of distribution on eld and inversely which means solving the two previous equations self-consistently. To solve the ICRF wave propagation (cf eq.1) we used the EVE code which is described in [19]. This full wave code calculates the wave electric eld by solving Maxwell's equations, using a variational principe. The quadratic dependence of the functional on the interaction Hamiltonian makes of EVE a second-order Finite Larmor Radius (FLR) code. The system of coordinates is (s, θ, ϕ), with s the radial coordinate, related to the poloidal ux by the relation ∇Ψ ≡ f (s) ∇s, and varying between 0 (centre) and 1 (edge) in the plasma volume. θ and ϕ are the poloidal and toroidal angles. The warm dielectric tensor in equation 1 is calculated assuming the heated distribution function is given by a bi-Maxwellian, i.e.
En savoir plus

20 En savoir plus

Large-Scale Collective Properties of Self-Propelled Rods

Large-Scale Collective Properties of Self-Propelled Rods

Noting that these differences reflect those in the lo- cal symmetry of particles and their interactions, a third situation can be defined, intermediate between the po- lar ferromagnetic model and the apolar nematic one, that of self-propelled polar particles aligning nematically [12]. Such a mechanism is typically induced by volume exclusion interactions, when elongated particles collid- ing almost head-on slide past each other, as illustrated schematically in Fig. 1. Thus, self-propelled polar point particles with apolar interactions can be conceived as a minimal model for self-propelled rods interacting by in- elastic collisions [13, 14, 15]. Other relevant situations
En savoir plus

6 En savoir plus

Calculation of a self-consistent, low frequency electrostatic field in the drift-kinetic approximation

Calculation of a self-consistent, low frequency electrostatic field in the drift-kinetic approximation

If we consider plasmas confined in tori, both for quasi-equilibria (including neoclassical transport theory) as well as for typical plasma instability phenomena in tor[r]

25 En savoir plus

Consistent Relations

Consistent Relations

Bossert, Sprumont and Suzumura (2005a) have characterized all notions of rational- izability when the coherence property required is consistency. As mentioned earlier, con- sistency and transitivity are equivalent in the presence of reflexivity and completeness. Thus, greatest-element rationalizability by a reflexive, complete and consistent relation is equivalent to greatest-element rationalizability by an ordering and Richter’s (1966; 1971) results apply; see the next theorem. Moreover, greatest-element rationalizability by a complete and consistent relation implies greatest-element rationalizability by a reflexive, complete and consistent relation, and greatest-element rationalizability by a consistent re- lation implies greatest-element rationalizability by a reflexive and consistent relation, and analogous observations apply in the case of maximal-element rationalizability; see Bossert, Sprumont and Suzumura (2005a, Theorem 1). As pointed out in Bossert, Sprumont and Suzumura (2006), as soon as the coherence properties quasi-transitivity or acyclicity are imposed, reflexivity no longer is guaranteed as an additional property of a rationaliza- tion. Thus, consistency stands out from these alternative weakenings of transitivity in this regard: as is the case for transitive greatest-element (or maximal-element) rational- izability, any notion of consistent greatest-element (or maximal-element) rationalizability is equivalent to the definition that is obtained if reflexivity is added as a property of a rationalization.
En savoir plus

22 En savoir plus

Heat Conduction and Entropy Production in Anharmonic Crystals with Self-Consistent Stochastic Reservoirs

Heat Conduction and Entropy Production in Anharmonic Crystals with Self-Consistent Stochastic Reservoirs

expressions g sc (x) can be analyzed in great detail, proving T r < T < T l . Acknowledgment. We thank Jonathan Mattingly and S.R.S. Varadhan for the help in the proof of the existence of the self-consistent profile. We also thank Herbert Spohn for useful discussions. The work of F. Bonetto was supported in part by NSF Grant DMS-060-4518, the work of J. L. Lebowitz was supported in part by NSF Grant DMR-044-2066 and by AFOSR Grant AF-FA 9550-04-4-22910, the work of J. Lukkarinen by Deutsche Forschungs- gemeinschaft (DFG) project SP 181/19-2 and by the Academy of Finland, the work of S. Olla by ANR LHMSHE no. BLAN07-2 184264 (France).
En savoir plus

26 En savoir plus

Self-consistent determination of line-width and probe shape using atomic force microscopy

Self-consistent determination of line-width and probe shape using atomic force microscopy

/ La version de cette publication peut être l’une des suivantes : la version prépublication de l’auteur, la version acceptée du manuscrit ou la version de l’éditeur.. For the publisher[r]

20 En savoir plus

Analytical parametrization of self-consistent polycrystal mechanics: Fast calculation of upper mantle anisotropy

Analytical parametrization of self-consistent polycrystal mechanics: Fast calculation of upper mantle anisotropy

S U M M A R Y Progressive deformation of upper mantle rocks via dislocation creep causes their constituent crystals to take on a non-random orientation distribution (crystallographic preferred orien- tation or CPO) whose observable signatures include shear-wave splitting and azimuthal de- pendence of surface wave speeds. Comparison of these signatures with mantle flow models thus allows mantle dynamics to be unraveled on global and regional scales. However, existing self-consistent models of CPO evolution are computationally expensive when used with 3-D and/or time-dependent convection models. Here we propose a new method, called ANPAR, which is based on an analytical parametrization of the crystallographic spin predicted by the second-order (SO) self-consistent theory. Our parametrization runs ≈2–6 × 10 4 times faster
En savoir plus

18 En savoir plus

Consistent Rationalizability

Consistent Rationalizability

Mots clés : choix rationnel, cohérence, domaines binaires ABSTRACT Consistency of a binary relation requires any preference cycle to involve indifference only. As shown by Suzumura (1976b), consistency is necessary and sufficient for the existence of an ordering extension of a relation. Because of this important role of consistency, it is of interest to examine the rationalizability of choice functions by means of consistent relations. We describe the logical relationships between the different notions of rationalizability obtained if reflexivity or completeness are added to consistency, both for greatest-element rationalizability and for maximal- element rationalizability. All but one notion of consistent rationalizability are characterized for general domains, and all of them are characterized for domains that contain all two-element subsets of the universal set.
En savoir plus

20 En savoir plus

Consistent rationalizability

Consistent rationalizability

Mots clés : choix rationnel, cohérence, domaines binaires ABSTRACT Consistency of a binary relation requires any preference cycle to involve indifference only. As shown by Suzumura (1976b), consistency is necessary and sufficient for the existence of an ordering extension of a relation. Because of this important role of consistency, it is of interest to examine the rationalizability of choice functions by means of consistent relations. We describe the logical relationships between the different notions of rationalizability obtained if reflexivity or completeness are added to consistency, both for greatest-element rationalizability and for maximal- element rationalizability. All but one notion of consistent rationalizability are characterized for general domains, and all of them are characterized for domains that contain all two-element subsets of the universal set.
En savoir plus

19 En savoir plus

Intraband transition in self-doped narrow band gap colloidal quantum dots

Intraband transition in self-doped narrow band gap colloidal quantum dots

ABSTRACT In this article we discuss the infrared properties of self-doped nanocrystals and in particular the case of HgSe. HgSe colloidal quantum dots have recently been reported for their tunable optical features all over the mid infrared from 3 to 20 µm. Their optical absorption is a combination of interband absorption at high energy and intraband absorption at low energy. The latter results from the self-doped character of HgSe. The origin of this self-doping is also discussed. We demonstrated that the doping results from the combination of the narrow band gap and high work function of HgSe, which leads to a reduction of the CQD by the water in the environment. In addition, we demonstrated that the doping density can be tuned over an order of magnitude thanks to the control of the capping ligands.
En savoir plus

7 En savoir plus

Large-scale networked systems: from anarchy to geometric self-structuring

Large-scale networked systems: from anarchy to geometric self-structuring

Large-scale networked systems: from anarchy to geometric self-structuring Anne-Marie Kermarrec, Achour Mostefaoui, Michel Raynal, Gilles Trédan, Aline Viana.. To cite this version: Anne-[r]

22 En savoir plus

SONDe, Self-Organizing Replica Placement in Large-Scale Dynamic Systems

SONDe, Self-Organizing Replica Placement in Large-Scale Dynamic Systems

We evaluate the algorithms along three metrics: i the number of rounds required to converge to a stabilized configuration; ii the reaction to load variations in term of number of created[r]

28 En savoir plus

Development and validation of the working memory self-assessment scale

Development and validation of the working memory self-assessment scale

REFERENCES •Baltes, P. B., & Baltes, M. M. (1990). Successful aging: Perspectives from the behavioral sciences. New York, NY : Cambridge University Press. •Bouazzaoui, B., Isingrini, M., Fay, S., Angel, L., Vanneste, S., Clarys, D., & Taconnat, L. (2010). Aging and self-reported internal and external memory strategy uses: The role of executive functioning. Acta Psychologica, 135, 59-66 • Kliegel, M., & Zimprich, D. (2005). Predictors of cognitive complaints in older adults : A mixture regression approach. European Journal of Aging, 2(1), 13-23. • Marcotte, T. D., & Grant, I. (2010). Neuropsychology of everyday functioning. New York, NY: The Guilford Press.
En savoir plus

1 En savoir plus

Show all 6869 documents...