The Experts below are selected from a list of 38904 Experts worldwide ranked by ideXlab platform
Thomas J Pence - One of the best experts on this subject based on the ideXlab platform.
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a structured continuum modelling framework for martensitic transformation and reorientation in shape memory materials
Philosophical Transactions of the Royal Society A, 2016Co-Authors: Davide Bernardini, Thomas J PenceAbstract:Models for shape memory material behaviour can be posed in the framework of a structured continuum theory. We study such a framework in which a scalar phase fraction field and a tensor field of martensite reorientation describe the material microstructure, in the context of finite strains. Gradients of the microstructural descriptors naturally enter the formulation and offer the possibility to describe and resolve phase transformation localizations. The constitutive theory is thoroughly described by a single free energy Function in conjunction with a path-dependent Dissipation Function. Balance laws in the form of differential equations are obtained and contain both bulk and surface terms, the latter in terms of microstreses. A natural constraint on the tensor field for martensite reorientation gives rise to reactive fields in these balance laws. Conditions ensuring objectivity as well as the relation of this framework to that provided by currently used models for shape memory alloy behaviour are discussed.
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models for one variant shape memory materials based on Dissipation Functions
International Journal of Non-linear Mechanics, 2002Co-Authors: Davide Bernardini, Thomas J PenceAbstract:Some simple models for the macroscopic behavior of shape memory materials whose microstructure can be described as a mixture of two phases are derived on the basis of a free energy and a Dissipation Function. Keeping a common expression for the free energy, each model is based on a different expression for the Dissipation Function. Temperature-induced as well as isothermal, adiabatic and convective stress-induced transformations are studied. Attention is paid to closed form solutions, comparison among the models and parameter identification.
Davide Bernardini - One of the best experts on this subject based on the ideXlab platform.
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a structured continuum modelling framework for martensitic transformation and reorientation in shape memory materials
Philosophical Transactions of the Royal Society A, 2016Co-Authors: Davide Bernardini, Thomas J PenceAbstract:Models for shape memory material behaviour can be posed in the framework of a structured continuum theory. We study such a framework in which a scalar phase fraction field and a tensor field of martensite reorientation describe the material microstructure, in the context of finite strains. Gradients of the microstructural descriptors naturally enter the formulation and offer the possibility to describe and resolve phase transformation localizations. The constitutive theory is thoroughly described by a single free energy Function in conjunction with a path-dependent Dissipation Function. Balance laws in the form of differential equations are obtained and contain both bulk and surface terms, the latter in terms of microstreses. A natural constraint on the tensor field for martensite reorientation gives rise to reactive fields in these balance laws. Conditions ensuring objectivity as well as the relation of this framework to that provided by currently used models for shape memory alloy behaviour are discussed.
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models for one variant shape memory materials based on Dissipation Functions
International Journal of Non-linear Mechanics, 2002Co-Authors: Davide Bernardini, Thomas J PenceAbstract:Some simple models for the macroscopic behavior of shape memory materials whose microstructure can be described as a mixture of two phases are derived on the basis of a free energy and a Dissipation Function. Keeping a common expression for the free energy, each model is based on a different expression for the Dissipation Function. Temperature-induced as well as isothermal, adiabatic and convective stress-induced transformations are studied. Attention is paid to closed form solutions, comparison among the models and parameter identification.
K C Le - One of the best experts on this subject based on the ideXlab platform.
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thermodynamic dislocation theory for non uniform plastic deformations
Journal of The Mechanics and Physics of Solids, 2018Co-Authors: K C LeAbstract:The present paper extends the thermodynamic dislocation theory developed by Langer, Bouchbinder, and Lookman to non-uniform plastic deformations. The free energy density as well as the positive definite Dissipation Function are proposed. The governing equations are derived from the variational equation. As illustration, the problem of plane strain constrained shear of single crystal deforming in single slip is solved within the proposed theory.
Daniele Rosato - One of the best experts on this subject based on the ideXlab platform.
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a rate dependent incremental variational formulation of ferroelectricity
International Journal of Engineering Science, 2011Co-Authors: Christia Miehe, Daniele RosatoAbstract:Abstract This paper presents a variational-based modeling and computational implementation of the non-linear, rate-dependent response of piezoceramics under electro-mechanical loading. The point of departure is a general internal variable formulation that describes the hysteretic electro-mechanical response of the material as a standard dissipative solid. Consistent with this type of dissipative continua, we develop a variational formulation of the coupled electro-mechanical boundary-value-problem based on incremental potentials for the stresses and the electric displacement. We specify the variational formulation to a model that describes time-dependent, electric polarizations accompanied by remanent strains. It is governed by a dual Dissipation Function formulated in terms of the internal driving forces. The model reproduces experimentally observed dielectric and butterfly hystereses, which are characteristic for ferroelectric materials. It accounts for the rate-dependency of the hystereses and the macroscopically non-uniform distribution of the polarization in the solid. An important aspect of our treatment is the numerical implementation of the coupled problem. The monolithic discretization of the two-field problem appears, as a consequence of the proposed variational principle, in a symmetric format. The performance of the proposed methods is demonstrated by means of a spectrum of benchmark problems.
Denis J Evans - One of the best experts on this subject based on the ideXlab platform.
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on the relationship between Dissipation and the rate of spontaneous entropy production from linear irreversible thermodynamics
Molecular Simulation, 2014Co-Authors: Stephen R Williams, Debra J Searles, Denis J EvansAbstract:When systems are far from equilibrium, the temperature, the entropy and the thermodynamic entropy production are not defined and the Gibbs entropy does not provide useful information about the physical properties of a system. Furthermore, far from equilibrium, or if the dissipative field changes in time, the spontaneous entropy production of linear irreversible thermodynamics becomes irrelevant. In 2000 we introduced a definition for the Dissipation Function and showed that for systems of arbitrary size, arbitrarily near or far from equilibrium, the time integral of the ensemble average of this quantity can never decrease. In the low-field limit, its ensemble average becomes equal to the spontaneous entropy production of linear irreversible thermodynamics. We discuss how these quantities are related and why one should use Dissipation rather than entropy or entropy production for non-equilibrium systems.
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on the probability of violations of fourier s law for heat flow in small systems observed for short times
Journal of Chemical Physics, 2010Co-Authors: Denis J Evans, Debra J Searles, Stephen R WilliamsAbstract:We study the statistical mechanics of thermal conduction in a classical many-body system that is in contact with two thermal reservoirs maintained at different temperatures. The ratio of the probabilities, that when observed for a finite time, the time averaged heat flux flows in and against the direction required by Fourier’s Law for heat flow, is derived from first principles. This result is obtained using the transient fluctuation theorem. We show that the argument of that theorem, namely, the Dissipation Function is, close to equilibrium, equal to a microscopic expression for the entropy production. We also prove that if transient time correlation Functions of smooth zero mean variables decay to zero at long times, the system will relax to a unique nonequilibrium steady state, and for this state, the thermal conductivity must be positive. Our expressions are tested using nonequilibrium molecular dynamics simulations of heat flow between thermostated walls.
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on the fluctuation theorem for the Dissipation Function and its connection with response theory
Journal of Chemical Physics, 2008Co-Authors: Denis J Evans, Debra J Searles, Stephen R WilliamsAbstract:Recently, there has been considerable interest in the fluctuation theorem (FT). The Evans-Searles FT shows how time reversible microscopic dynamics leads to irreversible macroscopic behavior as the system size or observation time increases. We show that the argument of this FT, the Dissipation Function, plays a central role in nonlinear response theory and derive the Dissipation theorem, giving exact relations for nonlinear response of classical N-body systems that are more widely applicable than previous expressions. These expressions should be verifiable experimentally. When linearized they reduce to the well-known Green-Kubo expressions for linear response.
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reversibility in nonequilibrium trajectories of an optically trapped particle
Physical Review E, 2004Co-Authors: James C Reid, D M Carberry, G M Wang, Edith M Sevick, Denis J Evans, Debra J SearlesAbstract:The fluctuation theorem (FT) describes how a system's thermodynamic irreversibility develops in time from a completely thermodynamically reversible system at short observation times, to a thermodynamically irreversible one at infinitely long times. In this paper, we present a general definition of the Dissipation Function ${\ensuremath{\Omega}}_{t}$, the quantitative argument in the fluctuation theorem (FT), that is a measure of a system's irreversibility. Originally cast for deterministic systems, we demonstrate, through the example of two recent experiments, that the Dissipation Function can be defined for stochastic systems. While the ensemble average of ${\ensuremath{\Omega}}_{t}$ is positive definite irrespective of the system for which it is constructed, different expressions for ${\ensuremath{\Omega}}_{t}$ can arise in stochastic and deterministic systems. Moreover, within the stochastic framework, ${\ensuremath{\Omega}}_{t}$ is not unique. Nevertheless, each of these expressions for ${\ensuremath{\Omega}}_{t}$ satisfies the FT.