Continuum Mechanics and Thermodynamics 

About: Continuum Mechanics and Thermodynamics is an academic journal published by Springer Science+Business Media. The journal publishes majorly in the area(s): Constitutive equation & Boundary value problem. It has an ISSN identifier of 0935-1175. Over the lifetime, 1619 publications have been published receiving 29374 citations.

The relaxation of a double-well energy

Abstract: This paper studies coherent, energy-minimizing mixtures of two linearly elastic phases with identical elastic moduli. We derive a formula for the “relaxed” or “macroscopic” energy of the system, by identifying microstructures that minimize the total energy when the volume fractions and the average strain are fixed. If the stress-free strains of the two phases are incompatible then the relaxed energy is nonconvex, with “double-well structure”. An optimal microstructure always exists within the class of layered mixtures. The optimal microstructure is generally not unique, however; we show how to construct a large family of optimal, sequentially laminated microstructures in many circumstances. Our analysis provides a link between the work of Khachaturyan and Roitburd in the metallurgical literature and that of Ball, James, Pipkin, Lurie, and Cherkaev in the recent mathematical literature. We close by explaining why the corresponding problem for three or more phases is fundamentally more difficult.

Modeling granular media on the computer

Abstract: Granular materials, like sand, powder or grains present intriguing phenomena. Vibration and shearing can lead to convective motion and segregation. A variation of stress may cause localization phenomena like stress chains or shear bands. Granular systems are thus in a state far from thermodynamic equilibrium, however, we present an attempt for a thermodynamic description by extending the concept of compactivity. In vibrating containers under the influence of gravity, the granular material shows a peculiar density profile. In the weak dissipation / strong agitation limit the density decays exponentially with height, whereas one observes an almost uniform profile in the case of strong dissipation / weak agitation. In the latter regime, the formation of convection cells due to walls or amplitude modulations can be observed. The onset of fluidization can be determined and is in good agreement with experiments. Connected to convection is the effect of rapid segregation, however, comparatively slow segregation can also be observed in the absence of convection. Numerical simulations of flow in hoppers show that the density fluctuations have a power spectrum, allowing for large “events” with finite probability. There is also ample experimental and numerical evidence showing the existence of spontaneous density patterns in granular material flowing through pipes or hoppers. Due to fluctuations of the wall friction, shock waves are created and arches are formed, slowing down the material which follows. In regions of anisotropic stress, the rotational degree of freedom is frustrated parallel to strong stresses, so that ordering akin to anti-ferromagnetic spin coupling may be observed. Pouring two different materials on a flat surface leads to a sandpile with stratification patterns. The mechanisms leading to this segregation of the two types are examined with experiments and numerical simulations. The stress distribution inside a sandpile depends strongly on the contact network. A relatively small polydispersity causes a reorganization of the contact network and leads to the so called stress chains, i.e. the stress at neighboring particles may vary dramatically. Finally, the plastic shear bands occuring in large scale deformations of compactified granular media are investigated by using an explicit Lagrangian technique as well as molecular dynamics simulations with non-spherical particles.

Heat pulse experiments revisited

Abstract: This is a review of heat propagation — theory and experiment — in dielectric solids at low temperatures where the phenomenon of second sound occurs. The review does not merely present a list of the various explanations of the observed phenomena. Rather it views them as special cases of a unified theory which is formulated within the framework of extended thermodynamics of phonos. Field equations are derived by averaging over the phonon-Boltzmann equation and initial and boundary value problems are solved. Thus it became possible to achieve a full explanation of the observations of the heat-pulse experiments in which ballistic phonons, second sound and ordinary heat conduction compete.