The structure of shock and interphase layers for a heat conducting Maxwellian rate-type approach to solid–solid phase transitions

We consider a thermoelastic model for phase transforming materials which can adequately describe the evolution with respect to the temperature of the hysteresis loop both in compression and tension tests. The specificity of this model is that the Grüneisen coefficient changes its sign. The model is augmented by considering a dissipative mechanism governed by a Maxwellian rate-type constitutive equation that can describe stress relaxation phenomena toward equilibrium between phases. Existence and uniqueness of traveling wave solutions are investigated. One derives that the admissibility condition induced by the Maxwellian rate-type approach, coupled or not with Fourier heat conduction law is related to the chord criterion with respect to the Hugoniot locus. We investigate the structure of profile layers, and we focus on their thermodynamic properties. The influence of the exothermic or endothermic character of phase transitions on the inner structure of interphase layers is captured. A phenomenon of temperature overshoot/undershoot with respect to the front state temperature and Hugoniot back state temperature inside an interphase layer is revealed.     

The asymptotics of correlation functions and liquid–vapor phase transitions

Power-law and exponential asymptotics of distribution functions are analyzed based on the Ornstein–Zernike equation. The correlation length at the critical point is shown to remain finite and, therefore, the partition function has no singularity at this point.     

High-pressure phase transitions and structure of Al–20 at % Si hypereutectic alloy

Phase transformations of an Al–20 at % Si high-silicon hypereutectic alloy have been studied by differential barothermal analysis at temperatures of up to 800°C in argon compressed to 100 MPa. High pressure has been shown to raise the melting point of the alloy by 5°C during heating and to lower the eutectic solidification temperature by 5°C during cooling in comparison with the canonical phase diagram of the Al–Si system. At a temperature of 553°C, heating and cooling lead to silicon dissolution and decomposition of the aluminum-based solid solution, respectively. After high-pressure solidification, the silicon particles in the alloy have a bimodal size distribution. Quantitative porosity characteristics in the alloy after a barothermal scanning cycle are similar to those in the as-prepared alloy. The lattice parameters of the silicon and aluminum remain unchanged. The microhardness of the aluminum matrix of the alloy corresponds to that of pure aluminum.     

Application of dilatometric analysis to the study of solid–solid phase transformations in steels

This article outlines the use of dilatometry in solid–solid phase transformation research in steel. It describes how dilatometric data are interpreted, with an emphasis on continuous heating and cooling transformation diagrams. These diagrams show the microstructural constituents that result from given heating and cooling conditions, and are an invaluable tool for the metallurgist in characterizing steels with respect to their response to heat treatments. Several practical examples and applications of dilatometry in steel research are briefly described in this work.     

Numerical modeling and simulation of a diffusion-controlled liquid–solid phase change in polycrystalline solids

A fully implicit two-dimensional moving-mesh finite element simulation model was developed to study the influence of grain boundaries in polycrystalline solids on diffusion-controlled liquid–solid transition during transient liquid phase (TLP) bonding. The new model, which was developed without the non-trivial symmetry assumption in existing numerical models for the process, was found to conserve solute and its calculated solutions were unconditionally stable and in good agreement with experimental results. Contrary to the assumption that increased grain boundary diffusion coefficient would significantly accelerate the rate of liquid–solid interface migration, numerical calculations and experimental verification showed that enhanced intergranular diffusivity had a minimal effect on the time required to achieve complete diffusion-induced solidification in cast superalloys. The results indicate that reducing the number of grain boundaries in structural alloys through directional solidification casting techniques did not constitute a disincentive to efficient application of TLP bonding to this class of materials.     

Studies of ferroelectric and magnetic phase transitions in multiferroic PbFe0.5Ta0.5O3–PbTiO3 solid solution ceramics

Dielectric, X-ray, Mossbauer and magnetization studies of (1 ? x)PbFe_0.5Ta_0.5O₃–(x)PbTiO₃ ceramics with 0 ≤ x ≤ 0.3 have been carried out to determine the compositional evolution of ferroelectric and magnetic phase transition temperatures. Addition of PbTiO₃ to PbFe_0.5Ta_0.5O₃ increases the temperature T _m of the dielectric permittivity maximum, decreases both the diffusion of this maximum and its frequency dependence. However, the Curie–Weiss temperature exceeds T _m for all the compositions studied, indicating that the phase transition still remains diffused. Dilution of the (Fe, Ta)-sublattice by Ti lowers the Neel temperature T _N but above a certain compositional threshold (x ≈ 0.1) fast lowering of T _N stops and a new magnetic state stable in a rather wide compositional range appears. Large difference between the zero-field-cooled (ZFC) and FC magnetization–temperature curves as well as between the temperatures of magnetic phase transition determined from Mossbauer and magnetization studies for compositions with x > 0.1 implies that this state is a spin-glass phase.     

Synthesis and thermal properties of polystyrene-graft-PEG copolymers as new kinds of solid–solid phase change materials for thermal energy storage

A series of polystyrene-graft-PEG₆₀₀₀ copolymers were synthesized as new kinds of polymeric solid–solid phase change materials (SSPCMs). The synthesized SSPCMs storage latent heat as the soft segments PEG₆₀₀₀ of the copolymers transform from crystalline phase to amorphous phase and therefore they can keep its solid state during the phase transition processing. The graft copolymerization reaction between polystyrene and PEG was verified by Fourier transform infrared (FT-IR) and ¹H NMR spectroscopy techniques. The morphology of the synthesized SSPCMs was characterized by polarization optical microscopy (POM). Thermal energy storage properties, thermal reliability and thermal stability of the synthesized SSPCMs were investigated by differential scanning calorimetry (DSC) and thermogravimetric (TG) analysis methods. The DSC results showed that the synthesized SSPCMs had typical solid–solid phase transition temperatures in the range of 55–58 °C and high latent heat enthalpy in the range of 116–174 J g⁻¹. The TG analysis findings showed that the synthesized SSPCMs had high thermal durability above their working temperatures. Also, thermal conductivity measurements indicated that the synthesized PCMs had higher thermal conductivity compared to that of polystyrene. The synthesized polystyrene-graft-PEG₆₀₀₀ copolymers as new kinds of SSPCMs could be used for thermal energy storage.     

Second phase structure effect to the failure of an Al–Si casting

An Al–Si casting (blower pump) failed during pressure test. The material of the casting was aluminum–silicon alloy (BS-LM 9), in solution treated and aged condition. During pressure test the casting failed around 130 bar, while it was designed to sustain a pressure of 160 bar.The failed body was examined with the help of stereo microscope, optical microscope and scanning electron microscope. Fracture started from a sharp edge of a race present at the interior of the body. A granular dull gray fracture surface was observed during unaided visual examination. Fractographic studies showed that the mode of the fracture was transgranular and the material failed in brittle mode. Optical microscopic examination showed a dendritic structure having a continuous network of the secondary phase. A sample taken from the fracture region unveiled the crack propagation along the secondary phase network. It was recommend to use modification process during melting practice to avoid the stress raisers.     

A new approach to establish both stable and metastable phase equilibria for fcc ordered/disordered phase transition: application to the Al–Ni and Ni–Si systems

Both two-sublattice (2SL) and four-sublattice (4SL) models in the framework of the compound energy formalism can be used to describe the fcc ordered/disordered transitions. When transferring the parameters of 2SL disregarding the metastable ordered states into those of 4SL, inconsistence in either stable or metastable phase diagrams could appear, as detected in both Al–Ni and Ni–Si systems. To avoid such a kind of drawback, this behavior was analyzed and investigated in the Ni–Si and Al–Ni systems with the aid of first–principle calculations. Furthermore, a new approach considering both the stable and metastable fcc ordered phase equilibria deduced from the first–principles calculations was proposed to perform a reliable thermodynamic modeling for the fcc ordered/disordered transition. The Ni–Si system was then thermodynamically assessed using the presently proposed approach. The good agreement between the calculation and experiments demonstrates the reliability of the proposed approach. It is expected that the approach is valid for other systems showing complex ordered/disordered transitions.     

The semicentralized approach to integrated water supply and treatment of solid waste and wastewater��a flexible infrastructure strategy for rapidly growing urban regions: the case of Hanoi/Vietnam

The development of the world population is characterized by an absolute population growth and a rapid urbanization. This process, taking place in Asia, Latin America, and Africa, poses major pressure on the affected urban regions. In Asian countries, this development is combined with high economic growth rates. At the same time, the climate change is proceeding, and the energy supply is going to become an existential problem. The rapidly growing cities therefore face the issue that the supply of infrastructures and public services lag behind the rapid urbanization. The increasing energy costs and the imperative to reduce the CO₂ emissions aggravate the situation. The centralized systems which started to be implemented in the industrialized countries more than 100?years ago are no longer the appropriate way to solve these problems. The semicentralized integrated approach, recently developed for rapidly growing urban regions in China, in contrast, offers with its flexibility a sustainable solution to cope with these developments. This article presents objectives and first results of an interdisciplinary R&D project aiming at the adaptation of the semicentralized integrated approach to the case of Hanoi, the rapidly growing capital of Vietnam, to contribute to the solution of the sanitation problems of both the old City Center and the urban expansions in conjunction. This article focuses on the planning and institutional aspects. The technical questions will be presented later in separate articles. The ongoing project is conducted by the Technische Universit?t Darmstadt in cooperation with the National University of Civil Engineering Hanoi and an industrial partner.     

The contribution of syntactic–semantic approach to the search for complementary literatures for scientific or technical discovery

The present paper tries to show that the current state of the art in syntactics and semantics, in computer systems based on the theory of inventive problem solving known as TRIZ, may help in the task of literature based discovery. With a structured and logic cause linkage between concepts, LBD could be faster and with less expert involvement at the beginning of the LBD process. The author tries to demonstrate the concept with two different problems: the hearing and balance problem known as Meniere’s disease, and to some of the current problems in the lithium air batteries for electric vehicles. By using open literature based discovery from An to Bn and from Bn to Cn, and with the logic relationships of real causes and effects approach, the author finds several relative new concepts such as vitamin A. Other concepts as niacin or fish oil, are also found, as potential to help in the Meniere’s disease. Secondly, using such procedure the author is able to find patents from disparate domain of expertise, as patents about odor control or metal casting.     

Laser shock peening effect on the dislocation transitions and grain refinement of Al–Mg–Si alloy

This paper systematically investigates the effect of laser shock peening without coating parameters on the microstructural evolution, and dislocation configurations induced by ultra-high plastic strains and strain rates. Based on an analysis of optical microscopy, polarized light microscopy, transmission electron microscopy observations and residual stress analysis, the significant influence of laser shock peening parameters due to the effect of plasma generation and shock wave propagation has been confirmed. Although the optical microscopy results revealed no significant microstructural changes after laser shock peening, i.e. no heat effect zone and differences in the distribution of second-phase particles, expressive influence of laser treatment parameters on the laser shock induced craters was confirmed. Moreover, polarized light microscopy results have confirmed the existence of well-defined longish grains up to 455 μm in length in the centre of the plate due to the rolling effect, and randomly oriented smaller grains (20 μm × 50 μm) in the surface due to the static recrystallization effect. Laser shock peening is reflected in an exceptional increase in dislocation density with various configurations, i.e. dislocation lines, dislocation cells, dislocation tangles, and the formation of dense dislocation walls. More importantly, the microstructure is considerably refined due to the effect of strain deformations induced by laser shock peening process. The results have confirmed that dense dislocation structures during ultra-high plastic deformation with the addition of shear bands producing ultra-fine (60–200 nm) and nano-grains (20–50 nm). Furthermore, dislocation density was increased by a factor of 2.5 compared to the untreated material (29 × 10¹³ m^− 2 vs. 12 × 10¹³ m^− 2).     

Study of a spherical head model. Analytical and numerical solutions in fluid–structure interaction approach

This paper deals with the analytical and the numerical computation of elastoacoustic vibration modes. We determine in the present study the eigenfrequencies and the modal shapes of the system of brain, cerebro-spinal fluid (CSF) and skull. Two models are presented in this work: an elastic-acoustic model assuming a rigid skull and an elastic-acoustic-elastic model assuming a deformable skull. The analytical results are compared with the numerical solution obtained using the software Comsol Multiphysics. It is shown that eigenfrequencies and more significantly the modal shapes are strongly influenced by the interaction between solid phases (brain and skull) and the cerebro-spinal fluid. Finally the influence of the CSF compressibility and thickness on the natural frequencies was investigated.     

Correlations between aging heat treatment, ω phase precipitation and mechanical properties of a cast Ti–Nb alloy

Ti–Nb alloys were arc melted in a water-cooled copper hearth in an inert atmosphere. After preparation, the samples were centrifugally cast in copper molds, and rapidly cooled, resulting in a martensitic microstructure. They were then aged at different temperatures. The microstructural characterization of this material suggested that martensite decomposition occurred, leading to precipitation of α, β and ω phases. Aging at higher temperatures led to ω phase decay. Mechanical characterization indicated that the heat treatment enhanced the strength and ductility of the alloys. Correlations between heat treatment, ω precipitation and mechanical behavior are discussed.     

Dynamic stiffness approach to vibration transmission within a beam structure carrying spring–mass systems

International Journal of Mechanics and Materials in Design - The dynamic stiffness method is developed for the dynamics of a beam structure carrying multiple spring?mass systems. Based on...