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UPCommons - E-prints UPC Universitat Politècnica de Catalunya (75,324 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 449

1. Mechanics and mechanisms of fatigue in a WC-Ni hardmetal and a comparative study with respect to WC-Co hardmetals - Tarragó Cifre, Jose María; Ferrari, Claudio; Reig, Begoña; Coureaux Mustelier, David; Schneider, Ludwig; Llanes Pitarch, Luis Miguel
There is a major interest in replacing cobalt binder in hardmetals (cemented carbides) aiming for materials with similar or even improved properties at a lower price. Nickel is one of the materials most commonly used as a binder alternative to cobalt in these metal-ceramic composites. However, knowledge on mechanical properties and particularly on fatigue behavior of Ni-base cemented carbides is relatively scarce. In this study, the fatigue mechanics and mechanisms of a fine grained WC-Ni grade is assessed. In doing so, fatigue crack growth (FCG) behavior and fatigue limit are determined, and the attained results are compared to corresponding fracture...

2. Mechanical properties of a new thermoplastic polymer orthodontic archwire - Varela, Juan Carlos; Velo, Marcos; Espinar Escalona, Eduardo; Llamas Carreras, Jose Maria; Rupérez de Gracia, Elisa; Manero Planella, José María; Gil Mur, Francisco Javier
A new thermoplastic polymer for orthodontic applications was obtained and extruded into wires with round and rectangular cross sections. We evaluated the potential of new aesthetic archwire: tensile, three point bending, friction and stress relaxation behaviour, and formability characteristics were assessed. Stresses delivered were generally slightly lower than typical beta-titanium and nickel-titanium archwires. The polymer wire has good instantaneous mechanical properties; tensile stress decayed about 2% over 2 h depending on the initial stress relaxation for up to 120 h. High formability allowed shape bending similar to that associated with stainless steel wires. The friction coefficients were lower than the...

3. Structure, deformation and fracture of arc evaporated Zr-Si-N hard films - Yalamanchili, K; Forsen, R; Jiménez Piqué, Emilio; Johansson Joesaar, M.P; Roa Rovira, Joan Josep; Ghafoor, N; Oden, M
Zr-Si-N films with varying Si contents were grown on WC-Co substrates by reactive cathodic arc deposition technique. The resulting microstructures of the films correlate to dominant variation in mechanical properties and deformation mechanisms. Si forms a substitutional solid solution in the cubic ZrN lattice up to 1.8 at.% exhibiting a fine columnar microstructure. Further Si additions result in precipitation of an amorphous (a)-SiNx phase and evolution of a nanocomposite microstructure (nc ZrN/a-SiNx) which completely suppresses the columnar microstructure at 63 at.% Si. The rotation-induced artificial layering during film growth is used as a marker to visualize the deformation of the...

4. Fracture and fatigue behavior of cement carbides:3D focused ion beam tomography of crack-microstructure interactions - Tarragó Cifre, Jose María; Jiménez Piqué, Emilio; Turón Viñas, Miquel; Rivero, Lorenzo; Al-Dawery, Ihsan; Schneider, Ludwig; Llanes Pitarch, Luis Miguel
The fracture and fatigue phenomena in WC-cobalt cemented carbides (hard-metals) have been subjects extensively investigated in the last 30 years. From these studies, it is well established that the metallic binder phase plays a key role as the toughening and fatigue-susceptible agent in these materials, as its effective ductility is critical for defining crack-growth resistance and cyclic-induced degradation. However, experimental proof of the role of toughening and fatigue micromechanisms has usually been presented on the basis of post-failure fractographic examination. In this work, the fracture and fatigue behavior of WC-cobalt is investigated and a 3D characterization of crack microstructure interaction...

5. Processing of alumina-zirconia composites by surface modification route with enhanced hardness and wear resistance - Kern, Frank; Palmero, Paola; García Marro, Fernando; Mestra Rodríguez, Álvaro Miguel
Zirconia toughened alumina (ZTA) materials are frequently used in mechanical engineering and biomedical applications due to their enhanced toughness, strength and wear resistance compared to monolithic alumina. In this study, a submicron size alumina powder was modified via wet chemical route: the alumina particles surface was coated with zirconium chloride, to yield 10 vol% zirconia by subsequent thermal treatment. From this powder, several ZTA materials were produced by slip casting, sintered at different temperatures from 1475 to 1575 degrees C. In all materials, a full characterization of their mechanical properties, microstructure and phase composition was carried out, together with wear...

6. Small-scale mechanical behavior of zirconia - Camposilvan, Erik; Torrents Abad, Oscar; Anglada Gomila, Marc
The surface stability of yttria-doped tetragonal polycrystalline zirconia is critical for load-bearing biomedical applications. In this work, the small-scale mechanical behavior of this material is probed by employing the in situ micro-cantilever bending technique to near-surface regions. Micro-cantilevers are milled by the focused ion beam technique in the as-sintered condition as well as after hydrothermal degradation by water vapor and tested in order to investigate the effect of degradation on the local flexural response. Results demonstrate that the technique is reliable for assessing the mechanical properties of thin superficial layers and their dependence on orientation. In the non-degraded material, the...

7. Influence of chemical composition and tempering treatment on toughness of bainitic 38MnV7 steel - Rancel, Lucia; Gómez, Manuel; Cabrera Marrero, José M.; Medina, Sebastián F.
This work studies the influence of Mn and the V/N ratio on the toughness of 38MnV7 steel. Four steels with different Mn, N and Ti contents were studied. Lowering the Mn content to approximately 1.5% considerably enhanced toughness by reducing Mn segregation and consequently achieved a more uniform bainitic microstructure. Rais ing the N content to reach a V/N ratio of close to 5 enhanced the intragranular nucleation of bainite and thus also improved toughness. Isothermal transformation prevented the presence of retained austenite and allowed a complete bainitic transformation. O ne of the steels contained Ti to control austenite grain growth by the precipitation of TiN particles. However,...

8. Electrospun gelatin/poly(epsilon-caprolactone) fibrous scaffold modified with calcium phosphate for bone tissue engineering - Rajzer, Izabella; Menaszek, Elzbieta; Kwiatkowski, Ryszard; Castaño Linares, Óscar; Planell Estany, Josep Anton
In this study gelatin (Gel) modified with calcium phosphate nanoparticles (SG5) and polycaprolactone (PCL) were used to prepare a 3D bi-layer scaffold by collecting electrospun PCL and gelatin/SG5 fibers separately in the same collector. The objective of this study was to combine the desired properties of PCL and Gel/SG5 in the same scaffold in order to enhance mineralization, thus improving the ability of the scaffold to bond to the bone tissue. The scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and the wide angle X-ray diffraction (WAXD) measurements confirmed that SG5 nanoparticles were successfully incorporated into the fibrous gelatin...

9. Calorimetric analysis of a Mg-Zn-Zr alloy processed by equal channel angular pressing via route A - Dumitru, Florina Diana; Ghiban, Brândusa; Cabrera Marrero, José M.; Higuera Cobos, Oscar Fabián; Gurau, Gheorghe; Ghiban, Nicolae
Being the lightest structural element, magnesium a nd its alloys has attracted significant interest in the last years, but because of its hexa gonal close packed structure, magnesium presents relatively low strength and ductility. One of the m ethods to improve the mechanical properties of the processed materials is through Severe Plastic D eformation (SPD). ZK60 magnesium alloy samples were subjected to 4 passes of equal-channel angular pressing (ECAP) at a processing temperature of 250°C, following route A. The micros tructure was determined with an Olympus BX51 optical microscope. Differential Scanning Calo rimetry (DSC) was used to estimate the stored energy and the recrystallization temperature after each ECAP pass

10. Strain hardening behavior of ARMCO iron processed by ECAP - Cabrera Marrero, José M.; Muñoz Bolaños, Jairo Alberto; Higuera Cobos, Oscar Fabián
The strain hardening behavior of an ARMCO iron processed by ECAP at room temperature up to sixteen passes following route Bc was investigated through Hollomon and differential Crussard-Jaoul models. Results indicate that the Hollomon analysis shows some deviations from the experimentally determined true stress – true strain curves while the differential Crussard-Jaoul analysis based on the Ludwik equation and the modified Crussard- Jaoul analysis based on the Swift equation fit better when two work hardening exponents are considered. As expected, the strength of the material increased with the number of ECAP passes. Indeed the ultimate tensile stress reached a maximum...

11. Influence of composition, grain size, and oxide particles on the strength of consolidated ball-milled iron - Benito Páramo, José Antonio; Cabrera Marrero, José M.; Casas, C.; Gregoire, V.
In this paper iron powders with two oxygen content (0.2 and 0.6% wt.) have been mechanically milled and consolidated by hot static pressing at different temperatures to obtain different grain sizes. At lower temperatures the grain size was in the nanostructured and ultrafine range and with increasing temperature abnormal grain growth was observed for both compositions. This led to the development of bimodal grain size distributions. In the samples with lower oxygen content the grain size and the percentage of coarse grain areas were larger than in the case of high oxygen content. The strength and ductility have been determined by...

12. Microstructural unit controlling cleavage crack propagation in high strength bainitic steels - Medina, Sebastián F.; Rancel, Lucia; Gómez, Manuel; Cabrera Marrero, José M.; Gutierrez, Isabel
The strengthening mechanisms which are operative in bainite are very well known: small bainite packet, small width of the laths, dislocation density and size and number of carbide particles (Fe 3 C), among others. Bainite packet size has been traditionally c onsidered as the value measured by optical microscopy (OM), as electron back scattered diffraction (EBSD) technique is relatively recent. In a V - microalloyed steel with bainitic microstructure of C=0.38% , V=0.12% and N= 0.0214% the average length and width of ferrite laths and of cementite carbides were measured. On the other hand, the bainite packet size was measured by OM and EBSD with a misorientation of 15º . These values of the microstructural units have been taken in account...

13. Alternative methods to attach components in printed circuit boards to improve their recyclability - Canal Marques, André; Cabrera Marrero, José M.; Malfatti, Célia de Fraga; Ortega Vega, Maria Rita
Printed circuit boards (PCB), which form the basis of the elect ronics industry, generate wastes that are difficult to dispose of and recycle due to the diversity of their materials and components and thei r difficult separation. The replacement of Pb-Sn welding for le ad-free alloys to attach components in printed circuit boards is an att empt to minimize the problem of Pb toxicity, but it does not ch ange the problem of separation of the components for later reuse and/or recycling. This article presents a review of the environmental problem of printed circuit boards, the initial development of alternative fixation studies, and reliability tests for comparison with con ventional boards and commercial systems to...

14. Hot ductility behavior of high-Mn austenitic Fe-22Mn-1.5Al-1.5Si-0.45C TWIP steels microalloyed with Ti and V - Salas-Reyes, A. E.; Mejía, Ignacio; Bedolla Jacuinde, Arnoldo; Boulaajaj, Ahmed; Calvo Muñoz, Jessica; Cabrera Marrero, José M.
This research work studies the influence of microalloying elements (Ti and V) and the solidification route on the hot ductility behavior of high-manganese TWIP steels. Uniaxial hot tensile tests in the temperature range of 700–1100 °C under a constant strain rate of 10-3 s-1 were carried out. Hot ductility as a function of reduction of area (RA) showed a significant improvement in the V-microalloyed TWIP steel, when compared to a non-microalloyed TWIP steel with a similar composition, in the intermediate temperature range of 800–900 °C. The highest value of 86% RA is attributed to the onset of dynamic recrystallization (DRX)...

15. Modeling of the hot flow behavior of advanced ultra-high strength steels (A-UHSS) microalloyed with boron - Mejía, Ignacio; Altamirano, G.; Bedolla Jacuinde, Arnoldo; Cabrera Marrero, José M.
In this research work, modeling of the hot flow behavior was carried out in a low carbon advanced ultra-high strength steels (A-UHSS) microalloyed with different amounts of boron (14, 33, 82, 126 and 214 ppm). For this purpose, experimental stress–strain data of uniaxial hot-compression tests over a wide range of temperatures (1223, 1273, 1323 and 1373 K (950, 1000, 1050 and 1100 °C)) and strain rates (10-3, 10-2 and 10-1 s-1) were used. The stress–strain relationships as a function of temperature and strain rate were successfully described on the basis of the approach proposed by Estrin, Mecking, and Bergström, together...

16. Texture and fatigue behavior of ultrafine grained copper produced by ECAP - Higuera Cobos, Oscar Fabián; Berríos-Ortiz, Jonathan Antonio; Cabrera Marrero, José M.
Electrolytic Tough Pitch (ETP) and Fire Refined High Conductivity (FRHC) copper samples were severely deformed by equal channel angular pressing (ECAP) and the effect of plastic deformation on the microstructure, texture and fatigue was investigated. The microstructural behavior was determined by analysis of the final texture through Inverse Pole Figures (IPF) and Orientation Distribution Function (ODF) maps, which revealed a marked decrease in the normal grain size of the ECAPed coppers and also the presence of recrystallization processes. The effect of the initial texture on the evolution of the texture after 8 ECAP passes for the two coppers was also...

17. Viabilidad del reaprovechamiento de residuos de PVC provenientes de cables eléctricos: propiedades mecánicas - Franco Urquiza, Edgar Adrian; Maspoch Rulduà, Mª Lluïsa
En este trabajo se han evaluado las propiedades mecánicas de desechos de cloruro de polivinilo (PVC) provenientes de cables eléctricos. El residuo contenía 60% de PVC, 30% de polietileno, 7% de goma y 3% de fracción metálica. La fracción metálica fue separada de forma manual. La recuperación de PVC se realizó mediante el método de flotación. Se prepararon 6 mezclas de PVC con residuo (R). El PVC y las mezclas se ensayaron a tracción, obteniendo una reducción de la resistencia y la ductilidad al incrementar el contenido de residuo. Esta reducción en las propiedades mecánicas se se halla relacionada con la heterogeneidad de los componentes de la mezcla.

18. Collagen-functionalised titanium surfaces for biological sealing of dental implants: Effect of immobilisation process on fibroblasts response - Marín Pareja, Nathalia; Salvagni, Emiliano; Guillem Martí, Jordi; Aparicio Bádenas, Conrado José; Ginebra Molins, Maria Pau
The clinical success of a dental implant requires not only an optimum osseointegration, but also the development of a biological sealing; i.e., a soft tissue seal around the transmucosal part of the implant. A promising approach to improve the biological seal of dental implants is the biomimetic modification of titanium surfaces with proteins or peptides that have specific cell-binding moieties. In this work we investigated the process of immobilising collagen on smooth and rough titanium surfaces and its effect on human dermal fibroblast (HDF) cell response. Titanium samples were activated by either oxygen plasma or acid etching to generate a...

19. Effect of Nb and Mo on the hot ductility behavior of a high-manganese austenitic Fe-21Mn-1.3Al-1.5Si-0.5C TWIP steel - Mejía, Ignacio; Salas Reyes, A.E.; Bedolla Jacuinde, Arnoldo; Calvo Muñoz, Jessica; Cabrera Marrero, José M.
This research work studies the influence of single microalloying elements (Nb and Mo) and the solidification route on the hot ductility behavior of a high-manganese austenitic Twinning Induced Plasticity (TWIP) steel. For this purpose uniaxial hot tensile tests in the temperature range of 700-1100 degrees C under a constant true strain rate (10(-3) s(-1)) were carried out to evaluate the hot ductility as a function of reduction in area (%RA). In general, results revealed a beneficial influence of Nb and Mo additions to TWIP steels on the hot ductility behavior, particularly in the intermediate temperature range of 800-900 degrees C,...

20. Isocyanate toughening of pCBT/organoclay nanocomposites with exfoliated structure and enhanced mechanical properties - Abt, Tobias Martin; Bou Serra, Jordi; Sánchez Soto, Miguel
Cyclic butylene terephthalate (CBT (R)) is an interesting matrix material for the preparation of nanocomposites due to its very low, water-like melt viscosity which favours clay exfoliation. Nevertheless, polymerized CBT (pCBT) is inherently brittle. This paper reports the preparation of isocyanate-toughened nanocomposites made from CBT and organo-modified montmorillonite. The role of the organoclay as reinforcement and the polymeric isocyanate (PMDI) as toughening agent on the properties of pCBT was studied. The organoclay increased the stiffness and strength by up to 20% whereas the PMDI improved the deformation behaviour. However, the PMDI did not affect the degree of clay dispersion or...

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