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UPCommons - E-prints UPC Universitat Politècnica de Catalunya (79,306 recursos)
E-prints UPC cobreix dues finalitats: per una banda, és el dipòsit institucional de la UPC que recull els articles de revista, les comunicacions de congrés i els reports de recerca generats en les activitats de recerca del personal docent i investigador de la universitat; per l'altra, és una eina que permet accelerar la producció científica, allotjant versions de documents prèvies a la publicació en una revista o a les actes d’un congrés.

Articles de revista

Mostrando recursos 1 - 20 de 470

1. Tendencias en el campo de la fundición inyectada - Martín Fuentes, Enrique; Menargues Muñoz, Sergi; Picas Barrachina, Josep Anton; Baile Puig, Maria Teresa
Este artículo recoge una visión actualizada de la problemática en el campo de la fundición inyectada, fundamentalmente en la industria de componentes de aluminio. Se muestran las principales limitaciones y se expone cómo la conformación en estado semisólido es una de las alternativas para resolver parte de esos inconvenientes.

2. Mechanical propertiesand in vitro biological response toporoustitaniumalloysprepared for useinintervertebralimplants - Caparrós Vázquez, Cristina Maria; Guillem Martí, Jordi; Molmeneu Trias, Meritxell; Punset Fusté, Miquel; Gil Mur, Francisco Javier
The generation of titanium foams is a promising strategy for modifying the mechanical properties of intervertebral reinforcements. Thus, the aim of this study was to compare the in vitro biological response of Ti6Al4V alloys with different pore sizes for use in intervertebral implants in terms of the adhesion, proliferation, and differentiation of pre-osteoblastic cells. We studied the production of Ti6Al4V foams by powder metallurgy and the biological responses to Ti6Al4V foams were assessed in terms of different pore interconnectivities and elastic moduli. The Ti6Al4V foams obtained had similar porosities of approximately 34%, but different pore sizes (66 µm for fine...

3. Properties of POSS blends with pCBT, PMMA, PC and POM thermoplastics - Abt, Tobias Martin; Sánchez Soto, Miguel; Illescas Fernandez, Silvia; Arostegui, Asier
The influence of the functionalisation of fully or partially condensed POSS cages on the properties of engineering thermoplastic-based nanocomposites is studied. POSS with different organic substituents were selected in accordance with the structure and chemical composition of the host polymer and melt mixed with the corresponding matrix. In general, good dispersion at the nanoscale level was achieved upon the addition of some functionalised POSS, leading to a remarkable increase on the thermal decomposition temperature under nitrogen atmosphere. However, for the polymers having high decomposition temperatures, there were no significant changes on the thermal properties of the nanocomposites. On the other hand, the dispersion of the POSS, whatever its functionalisation was,...

4. Influence of polyhedral oligomeric silsesquioxanes on thermal and mechanical properties of melt-mixed poly(methyl methacrylate)/polyhedral oligomeric silsesquioxanes composites - Illescas Fernandez, Silvia; Arostegui, Asier
In this study, the influence of the functionalization of fully or incomplete condensed polyhedral oligomeric silsesquioxanes composites (POSS) nanoparticles on the properties of poly(methyl methacrylate) (PMMA)-based composites has been studied. POSS with different organic substituents (methacryl, methacrylateisooctyl and trisilanolphenyl) are taken into account and added to the PMMA matrix by direct melt blending at loadings between 0 and 5 wt%. Significant differences in compatibility were observed depending on the structure of nanoparticles. POSS aggregation occurred during blending producing micron-sized aggregates in the composites. The thermal decomposition temperature of the composites with good dispersion of POSS aggregates increased under oxidative conditions....

5. Characterisation and modelling of prestrained viscoelastic films - Martinez-Agirre, Manex; Illescas Fernandez, Silvia; Elejabarrieta, María Jesús
The goal of the present work is to characterise the influence of static prestrain on the elastic and dissipative properties of constrained viscoelastic films. Dynamic mechanical analysis (DMA) technique is considered for measuring the dynamic properties under several static prestrain levels, and a new material constitutive model is presented for characterising the frequency–prestrain dependence of the viscoelastic material. The results indicate that the static prestrain strongly affects the elastic and dissipative properties of the analysed viscoelastic material. The proposed material constitutive model properly describes the frequency–prestrain dependence of the tested viscoelastic material.

6. Corrosion damage in WC-Co cemented carbides: residual strength assessment and 3D FIB-FESEM tomography characterisation - Tarragó Cifre, Jose María; Fargas Ribas, Gemma; Jiménez Piqué, Emilio; Felip, Alba; Isern, Lluis; Coureaux Mustelier, David; Roa Rovira, Joan Josep; Al-Dawery, Ihsan; Fair, Jonathan; Llanes Pitarch, Luis Miguel
The effect of corrosion damage on cemented carbides was investigated. The study included residual strength assessment and detailed fractographic inspection of corroded specimens as well as detailed 3D FIB-FESEM tomography characterisation. Experimental results point out a strong strength decrease associated with localised corrosion damage, i.e. corrosion pits acting as stress raisers, concentrated in the binder phase. These pits exhibit a variable and partial interconnectivity, as a function of depth from the surface, and are the result of heterogeneous dissolution of the metallic phase, specifically at the corrosion front. However, as corrosion advances the ratio between pit depth and thickness of...

7. High temperature scratch testing of hard PVD coatings deposited on surface treated tool steel - Pujante, Jaume; Vilaseca, Montserrat; Casellas, Daniel; Riera Colom, María Dolores
Scratch testing is one of the most usual characterisation techniques for systems with thin hard coatings. Scratch tests are performed at run at room temperature, due to the risk of degradation of the indenter diamond tip at high temperature and added test complexity. However, results obtained at room temperature may differ from the final system performance in high temperature applications, due to factors such as substrate thermal softening. In this work, a simple and a robust test for the mechanical characterisation of hard PVD coatings at high temperature and open atmosphere has been developed, based on a modification of the scratch...

8. Low Sr doping effects on critical current density and pinning mechanism of YBa2Cu3O7-x single crystals - Lopes, R.F.; Vieira, Valdemar das Neves; Teixeira Dias, Fábio; Silva, D.L.da; Pureur, P; Schaf, J; Roa Rovira, Joan Josep
We report on isotherm dc magnetization hysteresis loops, M(H) to 70K ¿ T ¿ 82.5K of YBa2-xSrxCu3O7-x (x = 0, 0.02 and 0.1) single crystals with the purpose to study the influence of the low Sr doping effects on the YBa2Cu3O7-¿ critical current density, JC(H) and normalized flux pinning force density, f(h). The M(H) measurements were performed in a commercial SQUID magnetometer with H ¿ 50kOe applied parallel to the c axis of the samples. The extended Bean critical state model was applied to JC(H) determination. The magnetic irreversibility fields, Hirr(T) were obtained from M(H) loops. The f(h) behavior was...

9. Correlation between electrical and mechanical properties in La1-XSrXGa1-YMgYO3-¿ ceramics used as electrolytes for solid oxide fuel cells - Morales Comas, Miguel; Roa Rovira, Joan Josep; Pérez Falcón, José Manuel; Moure Arroyo, Alberto; Tartaj, Jesus; Espiell Álvarez, Ferran; Segarra Rubi, Merce
The relation between the electrical and the mechanical properties in Sr and Mg doped LaGaO3 ceramics, which can be used as electrolyte for solid oxide fuel cells, was investigated in terms of hardness and ionic conductivity. For this purpose, ceramic materials corresponding to the compositions of La1 xSrxGa1 yMgyO3 d (LSGM), with x ¼ 0.1 and y ¼ 0.2, and x ¼ 0.15 and y ¼ 0.2, were prepared. LSGM powders synthesized by the ethylene glycol complex solution method were shaped into disks by isostatic pressing method. The variation in the microstructure of samples was achieved by varying the sintering temperature between...

10. Deformation mechanism induced under high cycle fatigue test in a metaestable austenitic stainless steel - Roa Rovira, Joan Josep; Fargas Ribas, Gemma; Jiménez Piqué, Emilio; Mateo García, Antonio Manuel
Advanced techniques were used to study the deformation mechanisms induced by fatigue tests in a metastable austenitic stainless steel AISI 301LN. Observations by Atomic Force Microscopy were carried out to study the evolution of a pre-existing martensite platelet at increasing number of cycles. The sub-superficial deformation mechanisms of the austenitic grains were studied considering the cross-section microstructure obtained by Focused Ion Beam and analysed by Scanning Electron Microscopy and Transmission Electron Microscopy. The results revealed no deformation surrounding the pre-existing martensitic platelet during fatigue tests, only the growth on height was observed. Martensite formation was associated with shear bands on...

11. Contact damage and fracture micromechanism of multilayered TiN/CrN coatings at micro- and nano-length scales - Roa Rovira, Joan Josep; Jiménez Piqué, Emilio; Martínez, R; Ramírez Sandoval, Giselle; Tarragó, Josep Maria; Rodríguez, R; Llanes Pitarch, Luis Miguel
In this study, systematic nanomechanical andmicromechanical studies have been conducted in threemultilayer TiN/CrN systems with different bilayer periods (8, 19 and 25 nm). Additionally, experimental work has been performed on corresponding TiN and CrN single layers, for comparison purposes. The investigation includes the use of different indenter tip geometries aswell as contact loading conditions (i.e. indentation/scratch) such to induce different stress field and damage scenarioswithin the films. The surface and subsurface damage under the different indentation imprints and scratch tracks have been observed by atomic forcemicroscopy, field emission scanning electron microscopy and focused ion beam. Multilayer TiN/CrN coated systems are found to exhibit higher adhesion strength (under...

12. New short T6 heat treatments for aluminium silicon alloys obtained by semisolid forming - Menargues Muñoz, Sergi; Martín Fuentes, Enrique; Baile Puig, Maria Teresa; Picas Barrachina, Josep Anton
In this work the heat treatment response of SSM processed A356 and A357 casting alloys was analysed. The development of a new T6 heat treatment, with solution times less than 30 mm has been allowed. In this new short heat treatment, the alloy showed better mechanical properties compared to the same alloy which heat treated in standard conditions (solution time between 6 h and 8 h). This new heat treatment, carried out at the solution temperature of 540 degrees C, enabled the complete magnesium dissolution, while minimizing the grain growth of the alpha-phase and the eutectic silicon. Although this experiment...

13. EBSD characterization of repetitive grain refinement in AZ31 magnesium alloy - Fatemi Varzaneh, S. M; Zarei Hanzaki, A; Cabrera Marrero, José M.; Rodríguez Calvillo, Pablo
A polycrystalline Mg-3Al-1Zn was subjected to high plastic strains by applying accumulative back extrusion (ABE) process. Electron back scatter diffraction analyses were used to explore the grain refinement mechanisms. A novel grain refinement trend was found at large strains, where new recrystallized grains were repetitively refined through dynamic recrystallization. The grain size was diminishing continuously up to the fourth ABE pass, after which no further grain refinement was noticed upon successive passes. (C) 2014 Elsevier B.V. All rights reserved.

14. Assessment in Si3N4 of a new method for determining the fracture toughness from a surface notch micro-machined by ultra-short pulsed laser ablation - Turón Viñas, Miquel; Anglada Gomila, Marc
The determination of the fracture toughness in a well characterized gas pressure sintered silicon nitride by the single edge V-notch beam method is analyzed in specimens with a surface shallow sharp notch produced by ultra-short pulsed laser ablation. The fracture surfaces and the damage in front of the notch tip are analyzed in detail by using focus ion beam/scanning electron microscopy and micro-Raman spectroscopy. It is concluded that the fracture toughness can be successfully determined by this technique and its importance for nano-grain size ceramics is outlined

15. Annealing aged zirconia: Study of surface mechanical properties at the micrometric length scale - Roa Rovira, Joan Josep; Anglada Gomila, Marcos Juan
The annealing of hydrothermal aged zirconia has been studied by analysing the changes in microstructure and surface mechanical properties in terms of the annealing temperature. In this experimental work, a systematic micro- and nanomechanical study has been conducted in 3 mol% yttria-stabilized tetragonal polycrystalline zirconia (3Y-TZP) aged at 134 degrees C for 60 h and annealed at 600 degrees C and 850 degrees C for 1 h. Advance characterization techniques (micro-Raman, field emission scanning electron microscopy and focused ion beam) have been used to study the near surface microstructural changes induced by these treatments. The mechanical properties and resistance to...

16. Biofunctionalization strategies on tantalum-based materials for osseointegrative applications - Mas Moruno, Carlos; Garrido, Beatriz; Rodríguez Rius, Daniel; Rupérez de Gracia, Elisa; Gil Mur, Francisco Javier
The use of tantalum as biomaterial for orthopedic applications is gaining considerable attention in the clinical practice because it presents an excellent chemical stability, body fluid resistance, biocompatibility, and it is more osteoconductive than titanium or cobalt-chromium alloys. Nonetheless, metallic biomaterials are commonly bioinert and may not provide fast and long-lasting interactions with surrounding tissues. The use of short cell adhesive peptides derived from the extracellular matrix has shown to improve cell adhesion and accelerate the implant’s biointegration in vivo. However, this strategy has been rarely applied to tantalum materials. In this work, we have studied two immobilization strategies (physical...

17. Estudio comparativo del conformado en caliente de un acero microaleado usando criterios termodinámicos continuos y criterios fenomenológicos - Alcelay Larrión, José Ignacio; Al Omar Mesnaoui, Anas; Prado Pozuelo, José Manuel
En las últimas décadas, los mapas de procesado han sido ampliamente utilizados para diseñar, controlar y optimizar los procesos de conformado en caliente. En el presente trabajo, se presenta un estudio comparativo entre mapas de procesado elaborados usando criterios termodinámicos continuos y criterios fenomenológicos. Por ello, se llevaron a cabo ensayos de compresión en caliente en el rango de temperaturas 900 - 1150 °C y de velocidades de deformación =10-4 - 10 s-1. El comportamiento en caliente del acero estudiado ha sido estudiado analizando las curvas de fluencia y la interacción entre el comportamiento microestructural y los parámetros de control...

18. Análisis multifactorial de la aplicación de metodologías activas en la calidad docente - Pérez Poch, Antoni; Sánchez Carracedo, Fermín; Salán Ballesteros, Maria Núria; López Álvarez, David
En este trabajo se realiza un análisis de los factores que más peso tienen en la mejora de la calidad docente en un contexto de enseñanza de la Informática y la Telemática en Grados de Ingeniería Industrial. El estudio se ha realizado en la Universitat Politècnica de Catalunya (UPC). Los autores son miembros de los grupos de innovación docente GIDMat, VISCA y GtPOE del proyecto RIMA (http://www.upc.edu/rima, Recerca i Innovació en Metodologies d’Aprenentatge). Se realiza también un análisis del impacto que se produce en la calidad docente al introducir técnicas de aprendizaje activo y cooperativo con autoevaluación y co-evaluación, así como la...

19. Compression properties and cellular structure of polyurethane composite foams combining nanoclay and different reinforcements - Sousa Pais Antunes, Marcelo de; Cano, Álvaro; Redondo Realinho, Vera Cristina de; Arencón Osuna, David; Velasco Perero, José Ignacio
In the present work we prepared and characterized several polyurethane (PU) composite foams by combining variable concentrations of nanoclay (montmorillonite, MMT) with metal wires or low cost cellulosic-based reinforcements, with the objective of developing multi-scalar rigid foams for structural applications. The addition of MMT promoted foaming and the formation of finer and more homogeneous cellular structures, resulting in foams with compressive elastic moduli and collapse stresses lower than that of the unfilled PU foams. However, a comparative analysis versus the foams’ relative density demonstrated that both mechanical properties follow one single trend for the two materials. The combination of MMT...

20. Cheaper membrane materials for microalgae dewatering - Nurra, Claudia; Franco Urquiza, Edgar Adrian; Maspoch Rulduà, Mª Lluïsa; Salvadó Rovira, Joan; Torras Font, Carles
Among different strategies to reduce costs in microalgae dewatering process via cross-flow filtration, the one related to membrane material was investigated in order to be decreased. Several materials were tested, starting with the ones commonly used in membrane technology [ceramic, polysulfone (PSf) and polyacrylonitrile (PAN)] to the ones generally employed in packaging industry [acrylonitrile butadiene styrene (ABS), glycol-modified polyethylene terephthalate (PETG) and polylactic acid (PLA)], the latter being considerably cheaper. Experiments carried out showed promising results in terms of permeabilities for PSf-Pluronic® F127 blended membranes and PAN membranes (11 ± 1 L/h/m2/bar and 22 ± 1 L/h/m 2/bar, respectively, instead...

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