Dynamic sensation of comfort in buildings : the temperature changes effects

The sensation of comfort in buildings depends on exter¬nal and internal variables: the well-known PMV method relates the expected temperature with the physiological behavior of the human body. Some models have discus¬sed the relevance of adaptation factors, in order to ex¬plain the higher expected “good” temperature of users living in warm climates. The same PMV method has been modified for these climatic situations. An adapta¬tion term has clearly to be considered, but other effects are important to determine the real expected temperatu¬re. In this paper temperature changes are considered to play an important role determining the expected “good” temperature. Effects of ventilation, rapid thermal chan¬ges when people move inside or outside of a building, continuous change in the temperature rate in the HVAC controlled spaces, are investigated here. Results show how to determine a dT/dt dependent term, which has to be considering in the PMV evaluation, in warm as in temperate climate. These results will be com¬pared with field studies for different climates. A PID (pro¬portional integrative derivative) correction in the PMV predict results seem to have to be expected, to consider at the same time adaptation and temperature rate effects.Postprint (published version

Cation distribution and high field magnetization studies on SrFe12-xCrxO19

With the aim of a better understanding of both cationic distribution and magnetic properties of the uniaxial SrFe12-xCrxO19hexagonal ferrites, Mössbauer spectroscopy, neutron diffraction and high field magnetization measurements have been carried out. The Cr3+ions occupy the octahedral sites of the M structure with a preference hierarchy within them. The magnetic measurements, together with the deduced cationic distribution, indicate that some sublattices have a random spin canting around the c-axis

Matériaux intelligents : modélisation prédictive de l’évolution temporelle d’alliages à mémoire de forme du type Cu-Zn-Al

Les propriétés «intelligentes» de certains matériaux (magnétostriction, piézoélectricité, mémoire de forme) concernent leur capacité à réagir directement à une modification de leur environnement. L'application pratique des alliages à mémoire de forme nécessite des outils de caractérisation permettant une évaluation quantitative des performances en vue de garantir l'utilisation de ces matériaux. Une étude, de haute résolution, de leur comportement temporel permet une modélisation prédictive de celui-ci et l'établissement éventuel de routines industrielles de contrôle. Lorsque le matériau se trouve en phase-mère, un changement de la température ambiante produit, sur la température de transformation, un changement égal à 11 % de celui qui affecte la température ambiante

Physics laboratory experiments at the Barcelona Faculty of Nautical Studies

Postprint (author's final draft

Anisotropic Behaviour in Cu-Zn-Al SMA Due to the Oriented Growth of γ Precipitates

The two way shape memory effect (TWSME) is usually induced by the presence of either stabilized thin plates of martensite or particular defects breaking the symmetry of the parent phase and making only one or a few variants favourable upon transformation. Generally, the defects are created in the material by performing a certain number of transformation cycles. An alternative method to induce the TWSME, avoiding the heavy training processes, has been obtained for Cu-Zn-Al single crystal . It consists on the introduction of small γ precipitates by apropriated thermal treatments. Then the precipitates are made to grow asymmetrically by the action of an applied stress. Anisotropic residual stresses then favour the appearance of some selected martensite variants at the transformation cycles

NiTi thermal sprayed coatings characterization

NiTi alloy has been particularly studied over many years for its shape memory properties and excellent corrosion resistance and biocompatibility, thus making it suitable for many biomedical applications. Then, bulk material properties have been well characterized depending on the nominal composition, manufacturing method and thermal treatments. It has been, however, less studied the use of such alloy in its overlay form, many times just employing Vacuum Spraying (VPS) for thick coatings in order to avoid Ti oxidation. The present study explores and compares the spraying of atomized NiTi powders by VPS as well as by Atmospheric Plasma Spraying (APS) and High Velocity Oxygen Fuel (HVOF). X-ray diffraction studies conducted at –100 and 100°C revealed that the feedstock powder presented a metastable rhombohedral NiTi phase at low temperatures and at room temperatures and higher the result was beta phase. DSC experiments also supported the previous phase transformations. After spraying, according to the thermal history of the particles in each spraying technology, it is observed the retention of the β-NiTi feedstock phase as well as the appearance of metastable phases, amorphization and nanocrystalline areas. Also with XRD at different temperatures and, especially in the case of the HVOF coating, due to the moderate heat input of the process, the final results fairly agreed with those of the original powder

Fundamental aspects on the thermoelasticity and pseudoelasticity in single interface transformations

The thermoelasticity in the $\beta$$\rightarrow$2H single interface transformation in a Cu-Zn-A1 alloy was studied. The coefficient of thermoelasticity was found to be much smaller than that of the $\beta$$\rightarrow$18R transformation. It was found that stacking faults are indeed created from the interaction of the 2H martensite with the existing dislocations. However the 2H martensite, at variance with the 18R martensite, is twinned. Consequently the stacking faults are not dragged by the moving interface, instead they end at some of the twin interfaces in each twin variant. In conclusion there is no, or little, contribution of the stacking faults to the thermoelasticity