Phenomenological Phase Transition Research Articles

Magnetocaloric effect and magnetic phase diagram of Ni-Mn-Ga Heusler alloy in steady and pulsed magnetic fields

The work is devoted to the study of the phenomenon of irreversibility of the magnetocaloric effect (MCE) in the vicinity of the magnetostructural phase transition (PT) in Ni-Mn-Ga Heusler alloys. For this purpose, the MCE was studied by the direct method in stationary (up to 14 T) and pulsed magnetic fields (up to 50 T), and a magnetic phase diagram was constructed. Using a specially designed microscope, in-situ studies of the magnetostructural phase transition were carried out in magnetic fields of up to 14 T. Comparing the results of the MCE with those of the phase diagram, as well as in-situ studies, made it possible to determine the width of the irreversible MCE region. In-situ studies have shown, that the main reason of the occurrence of the irreversible MCE is the presence of the residual martensite formed as a result of the first magnetization of the sample. The results are discussed within the framework of Landau's phenomenological PT theory, which predicts the disappearance of thermal hysteresis under a field of 30 T. Within the framework of the same theory, a recommendation is made to reduce the value of the critical field and, as a result, the width of the hysteresis.

Thermodynamic and viscoelastic constitutive model of TPI/HDPE hybrid shape memory polymer

In recent years, shape memory smart materials have developed rapidly, and more and more novel shape memory polymers have been developed and applied. In sharp contrast to the rapid development of shape memory smart materials, its theoretical research is obviously lagging behind. Therefore, it is necessary to clearly understand and master the thermodynamic dynamic response mechanism of shape memory polymers. In view of the fact that the influence of thermodynamic properties of hybrid shape memory polymer under the coupling effect of multiple factors is still very vague, a novel hybrid shape memory polymer composites (SMPC) thermodynamic viscoelastic constitutive model is proposed for the first time by combining the macroscopic phenomenological viscoelastic theory with the microscopic phenomenological phase transition model, and a microstructure composed of two parts of reversible phase and stationary phase in parallel is constructed. At the same time, a three-dimensional parameter equation with temperature effect and capable of describing the coordinated changes of various parameters in the phase transition process is established. Through the validation of the model, it can be found that the variation trend of the simulation curve is in good agreement with the experimental curve during the whole static loading process, and the error of the fracture stress is less than 2%. Through the dynamic evolution of multi-content and wide-temperature range, the consistency between the simulation results and the experimental results is successfully proved, and the microscopic mechanism of the macroscopic static mechanical behavior of the hybrid SMPC is revealed. The model established in this paper can accurately describe the internal phase change of the mixed matrix, and realize the effective prediction of the stress-strain response under the coupling effect of the matrix composition and the external environment. The proposal of this model provides a new idea for the exploration of hybrid SMPC thermodynamic viscoelastic theory, and also provides an important theoretical reference for the development and application of novel hybrid shape memory materials in the future.

Lattice dynamics and phase stability of rhombohedral antimony under high pressure

The high pressure lattice dynamics of rhombohedral antimony have been studied by a combination of diffuse scattering and inelastic x-ray scattering. The evolution of the phonon behavior as function of pressure was analyzed by means of two theoretical approaches: density functional perturbation theory and symmetry-based phenomenological phase transition analysis. This paper focuses on the first structural phase transition, SbI-SbIV, and the role of vibrations in leading the transition. The phonon dispersion exhibits complex behaviour as one approaches the structural transition, with the branches, corresponding to the two transitions happening at high pressure in the Va elements (A7-to-BCC and A7-to-PC) both showing softening.

Phenomenological modelling of phase transitions with hysteresis in solid/liquid PCM

Technical-grade and mixed solid/liquid phase change materials (PCM) typically melt and solidify over a temperature range, sometimes exhibiting thermal hysteresis. Three phenomenological phase transition models are presented which are directly parametrized using data from complete melting and solidification experiments. They predict hysteresis phenomena and are used to calculate effective PCM properties. Two models have already been implemented in commercial building simulation and/or multiphysics software, but not the third novel model. Applications are presented for two commercial PCM: a paraffin, and a salt water mixture with additives. Numerical implementation aspects are discussed, and significant differences in the predicted absorbed and released heat are highlighted when simulating consecutive incomplete phase transitions. The models are linked with energy balance equations to predict recorded PCM temperatures of a thermal energy storage. The cross-validation with data from 26 partial load conditions clearly indicate a superior predictive performance of the novel hysteresis model.

Classification of phenomenological phase transition models by the methods of equivariant catastrophe theory: Models with L = C nv (n = 3, 4, 6)

A classification of phenomenological phase-transition models for the two-component order parameter by the methods of equivariant catastrophe theory is proposed. The models are constructed on the basis of the number of thermodynamic parameters that are varied in an experiment (temperature, pressure, chemical potentials of admixtures, etc.) instead of the simple expansion of the thermodynamic potential in an order parameter power series. The classification of models with the order parameter symmetry groups L = Cnv (n = 3, 4, 6) with the number of varied parameters from 1 to 5 is performed.

An investigation on the field strength and loading rate dependences of the hysteretic dynamics of magnetorheological dampers

This paper is an extended study on the model of the hysteretic dynamics of magnetorheological dampers based on a phenomenological phase transition theory (Wang and Kamath in Smart Mater. Struct. 15(6):1725–1733, 2006). It is demonstrated that, by appropriately choosing model parameters, the frequency dependence of the hysteretic dynamics can be captured very well by the model based on phase transition theory. Whilst by introducing an appropriate rescaling coefficient to account for the strength of the magnetized particle chains with various magnetic field strengths, the field strength dependence of the hysteretic dynamics can also be captured very well by the same differential equation with the same set of model parameters. There are in total eight model parameters introduced for capturing the hysteretic dynamics, including its dependence on the loading rate and field strength.

Dynamic Models for Magnetorheological Dampers and its Feedback Linearization

In the current paper, the hysteretic dynamics of magnetorheological dampers is modeled by a differential model. The differential model is constructed on the basis of a phenomenological phase transition theory. The model is expressed as a second order nonlinear ordinary differential equation with bifurcations embedded in. Due to the differential nature of the model, the hysteretic dynamics of the MR dampers can be linearized and controlled by introducing a feedback linearization strategy.

Electric field induced collapse of the charge-ordered phase in manganites

The colossal electroresistance in manganites accompanies the insulator-to-metal phasetransition induced by the electric field. A phenomenological phase transition model isproposed to study this electric field induced collapse of the charge-ordered phase. Thehysteresis of the phase transition is well explained using the effective mediumapproximation. The volume fraction of the metallic region at the metal-to-insulatortransition point is estimated as 30%.

CURVATURE EFFECTS IN CLUSTERS GROWN IN A 2D DISCRETE SPACE: AN ALGEBRAIC APPROACH

According to a phenomenological phase transition mechanism introduced quite recently, we propose a systematic examination of the polymorphic contraction–expansion effects observed for a broad class of morphologies with nonvanishing surface (line) tension. In our mean-field approach, we are looking for the line order parameter behavior as a function of a thermodynamic control parameter at a fixed number of entities consituting the morphology as a whole. We also wish to somehow invert the problem, and will be looking for some evolution going via a set of quasi-equilibrium states while fixing the control parameter. Both the situations considered are of interest for studying the so-called morphology diagrams as well as, to some extent, for describing selected model evolutions in a two-dimensional microworld, e.g., in nanoscale, where biomembranes and interfaces are presently of special attention.

A phenomenological phase transition model for heavy particles

Modele phenomenologique pour les proprietes thermodynamiques et de transport des fermions lourds, dans lequel la longueur de coherence est supposee etre l'analogue de la longueur de correlation dans la transition de phase intervenant a zero Kelvin

Phenomenological phase transition approach to the two-component Rayleigh-Bénard problem: Tricritical behavior

A previously introduced Landau “potential” for the description of the basic features of the two-component Rayleigh-Benard problem is shown to be endowed with the relevant properties of the classical Landau singular free energy used in the study of equilibrium tricritical phenomena. Predictions of relevance to experiments on convective instability are also given.