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UPCommons - E-prints UPC Universitat Politècnica de Catalunya (59.763 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 341

1. Thermal stability and fire behaviour of flame retardant high density rigid foams based on hydromagnesite-filled polypropylene composites - Redondo Realinho, Vera Cristina de; Haurie Ibarra, Laia; Sousa Pais Antunes, Marcelo de; Velasco Perero, José Ignacio
The present work deals with the development of new rigid polypropylene composite foams filled with high amounts of flame-retardant systems based on synthetic hydromagnesite, a basic magnesium carbonate obtained from an industrial by-product. A partially-interconnected cellular structure with a cell size around 100 μm was obtained for the hydromagnesite-filled PP foams. A 40% reduction of this cell size was observed when a small amount of a combination of montmorillonite and graphene layered nanoparticles was added to the hydromagnesite. The combination of hydromagnesite with an intumescent additive (ammonium polyphosphate) and layered nanoparticles led to improved thermal stability. In particular, the intumescent...

2. Nanoindentation of nanocolumnar TiO2 thin films with single and stacked zig-zag layers - Jiménez Piqué, Emilio; Gonzalez Garcia, Lola; Rico, Victor J.; Rodriguez Gonzalez-Elipe, Agustin
This paper reports a systematic analysis of the mechanical properties of nanocolumnar TiO2 thin films prepared by evaporation at a glancing geometry. A systematic study of the mechanical properties is carried out by comparing the hardness and the Young's modulus determined by nanoindentation for thin films prepared at different deposition angles and characterized by a tilted nanocolumnar structure and others where the nanocolumns are perpendicular to the substrate or are arranged as zig-zag stacked layers. A correlation between mechanical properties and glazing angle geometry is proposed. Differences in the results are discussed in view of the cross section images obtained...

3. Deformation mechanisms induced under high cycle fatigue tests in a metastable 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...

4. Analysis of the misfit of dental implant-supported prostheses made with three manufacturing processes - Fernández Yagüe, Marc-Antoni; Delgado Garoña, Luis María; Molmeneu Trias, Meritxell; García, David; Rodríguez Rius, Daniel
The microgap between implant components has been associated with complications such as screw loosening or adverse biologic responses.

5. Fracture toughness reliability in polycarbonate: notch sharpening effects - Salazar, Alicia; Rodríguez, Jesús; Martínez Benasat, Antonio
The effect of the notch sharpening on the fracture toughness obtained under linear elastic fracture mechanics has been analyzed in an amorphous polycarbonate. The samples for fracture characterization were sharpened via the traditional contact steel razor blade technique and the noncontact femtosecond laser ablation technique. The values of the fracture toughness of the specimens sharpened through femtosecond laser ablation were lower than those measured on samples sharpened using a steel razor blade. Moreover, the former was in plane strain state, but the latter did not verify the size criterion. The damage produced ahead of the crack tip through plastic deformation...

6. Effect of the thermoforming process variables on the sheet friction coefficient - Morales, Rosa Amalia; Candal Pazos, Maria Virginia; Santana Pérez, Orlando Onofre; Gordillo Aubert, Antonio; Salazar, Rubén
The objective of this work was to obtain, through a simple experimental assembly, the real influence of the friction and process conditions in the assisted thermoforming process. The use of simulation tools to optimize this process requires the knowledge of the sheet-plug system friction coefficient [μ], the used temperature and velocity conditions, and due to that, the software does not have a wide database. For this, the users suppose μ with the previous known difference between the simulated and the experimental data. For this reason, the obtaining of μ may allow to achieve more accurate simulations. In this work, a...

7. Improvement of mechanical properties on metastable stainless steels by reversion heat treatments - Mateo García, Antonio Manuel; Zapata, A.; Fargas Ribas, Gemma
AISI 301LN is a metastable austenitic stainless steel that offers an excellent combination of high strength and ductility. This stainless grade is currently used in applications where severe forming operations are required, such as automotive bodies. When these metastable steels are plastically deformed at room temperature, for example by cold rolling, austenite transforms to martensite and, as a result, yield strength increases but ductility is reduced. Grain refinement is the only method that allows improving strength and ductility simultaneously. Several researchers have demonstrated that fine grain AISI 301LN can be obtained by heat treatment after cold rolling. This heat treatment is called reversion because it provokes the reversion of...

8. Martensitic transformation during fatigue testing of an AISI 301LN stainless steel - Mateo García, Antonio Manuel; Fargas Ribas, Gemma
The plastic deformation accumulated during fatigue testing can induce the transformation of austenite to martensite in metastable austenitic stainless steels. To analyze this issue, a metastable austenitic stainless steel grade AISI 301 LN was studied in two different conditions, i.e. annealed and cold rolled. In the first case, the steel was fully austenitic, whereas cold rolled material had almost 30% of martensite. High cycle fatigue tests at a stress ratio of 0.8 were carried out on flat specimens from both steel conditions. Several characterization techniques, including optical microscopy, X-ray diffraction (XRD) and electron back scattered diffraction (EBSD), were used to...

9. Effect of temperature on the orthodontic clinical applications of NiTi closed-coil springs - Espinar, Eduardo; Llamas Carreras, Jose Maria; Barrera Mora, Jose Maria; Ábalos, C.; Gil Mur, Francisco Javier
NiTi spring coils were used to obtain large deformation under a constant force. The device consists on a NiTi coil spring, superelastic at body temperature, in order to have a stress plateau during the austenitic retransformation during the unloading. The temperature variations induced changes in the spring force. Objectives: The aim of this study is to investigate the effect of the temperature variations in the spring forces and corrosion behaviour simulating the ingestion hot/cold drinks and food. Study D esign: The springs were subjected to a tensile force using universal testing machine MTS-Adamel (100 N load cell). All tests were performed in artificial saliva maintained at different temperatures....

10. Efecto del tratamiento de anodizado en las propiedades de la aleación EN-AC46500 conformada en estado semisólido - Baile Puig, Maria Teresa; Picas Barrachina, Josep Anton; Menargues Muñoz, Sergi; Martín Fuentes, Enrique
En este trabajo se ha estudiado el efecto del tratamiento de anodizado en las propiedades superficiales de componentes AlSi conformados en estado semisólido. Los componentes fueron conformados mediante una máquina de inyección a alta presión y una estación Idra de Semi Solid Rheocasting (SSR), empleando una aleación de segunda fusión EN AC- 46500. Las muestras se trataron térmicamente con el objetivo de modificar la forma y la distribución del silicio eutéctico, y posteriormente fueron granalladas para obtener distintas rugosidades. Finalmente, los componentes fueron anodizados con el propósito de mejorar sus propiedades tribológicas y la resistencia a la corrosión. Para ello, se llevaron a cabo antes y después del proceso de anodizado, ensayos de desgaste con...

11. Depth-sensing indentation applied to polymers: A comparison between standard methods of analysis in relation to the nature of the materials - Giró Paloma, Jessica; Roa Rovira, Joan Josep; Díez Pascual, Ana Maria; Rayón Encinas, Emilio; Flores Aguilar-Amat, Araceli; Martínez López, Monica; Chimenos Ribera, Josep M.; Fernández Renna, Ana Ines
Mechanical data (hardness and elastic modulus) from instrumented indentation testing are often extracted assuming linear elasticity in the initial portion of the unloading. The method is nowadays widely accepted as a convenient tool to interpret depth-sensing data, however it is a matter of controversy when applied to polymer materials due to their time- dependent behavior. More recently, Loubet and co-workers applied continuous stiffness measurements (CSM), consisting of superimposing a small oscillation to the quasi-static component of loading, to the study of the mechanical properties of polymers and proposed a new model to account for the apparent increase in the contact area detected at the first stages of contact....

12. NiTi superelastic orthodontic wires with variable stress obtained by ageing treatments - Gil Mur, Francisco Javier; Cenizo, M.; Espinar, Eduardo; Rodríguez Contreras, Alejandra María; Rupérez de Gracia, Elisa; Manero Planella, José María
A new strategy to obtain NiTi orthodontic archwires with variable correcting stresses in different segments is presented. Different heat treatments are applied in selected segments, which produce variations in the superelastic properties. These allow to modulate the correcting stresses to the requirements of the specific teeth. This method avoids laser welding, which is associated with corrosion and brittleness problems. The aim of this study is to analyze the effect of the heat treatment by zones on transformation temperatures, and stresses in NiTi orthodontic archwires with identical chemical composition. A reduction of the Ti content is observed, in the matrix of...

13. Injectable collagen/alpha-tricalcium phosphate cement: collagen-mineral phase interactions and cell response - Perez Antoñanzas, Roman; Ginebra Molins, Maria Pau
A bone inspired material was obtained by incorporating collagen in the liquid phase of an a -trical- cium phosphate cement, either in solubilized or in fibrilized form. This material was able to set in situ, giving rise to a calcium deficient hydroxyapatite (CDHA)/collagen com- posite. The morphology and distribution of collagen in the composite was shown to be strongly affected by the col- lagen pre-treatment. The interactions between collagen and the inorganic phase were assessed by FTIR. A red shift of the amide I band was indicative of calcium chelation by the collagen carbonyl groups. The rate of CDHA formation was not affected when diluted collagen solutions (1 mg/ml) were used, whereas injectability improved....

14. Hydrothermal ageing of cracked of 3Y-TZP - García Marro, Fernando; Mestra Rodríguez, Álvaro Miguel; Anglada Gomila, Marcos Juan
En la circona dopada con 3% molar de itria, el vapor de agua puede inducir la transformación de la fase tetragonal a monoclínica en la superficie. Dicha transformación se ex tiende hacia el interior acompañada por la aparición de microfisuras, lo que induce una pérdida de la integridad es tructural. Este fenómeno de degradación a baja temperatura (LTD) es una clara desventaja para la utilización del material en atmósferas húmedas. Sin embargo, el efecto del agua sobre grietas de indentación no ha sido estudiado. Este trabajo estudia la influencia de LTD en la resistencia mecánica de dichas grietas. Los resultados muestran sorprendentemente un incremento de la resistencia mecánica...

15. Daño por contacto hertziano en un nanocompuesto Ce-TZP/Al2O3 - García Marro, Fernando; Mestra Rodríguez, Álvaro Miguel; Anglada Gomila, Marcos Juan
El material compuesto Ce-TZP/Al 2 O 3 es una cerámica nanoestructurada con granos de alúmina y circona tetragonal estabilizada con ceria. Actualmente, este tipo de compuestos están siendo desarrollados con el objetivo de sustituir a la circona dopada con 3% molar de itria de grado biomédico. En este trabajo, se ha estudiado el comportamiento de este compuesto bajo contacto monotónico apli cado mediante indentación esférica. Me diante espectroscopia micro-Raman se ha puesto en evidencia el cambio de fase local inducido por acción de las tensiones en la huella residual. Esto indica que el mecanismo de transformación de fase es máximo en los bordes de la huella, que corresponde a la zona donde...

16. Decoration of indentation cracks in 3Y-TZP by hydrothermal ageing - García Marro, Fernando; Camposilvan, Erik; Mestra Rodríguez, Álvaro Miguel; Anglada Gomila, Marcos Juan
Las grietas de indentación en cerámicas son frecuen temente utilizadas no sólo para estimar semi-empíri camente la tenacidad a fractura K IC , sino también cómo método para crear grietas aguda s superficiales y semielípticas a partir de las cuales analizar la tenacidad de fractura. Para ello es necesario conocer la forma exacta de la grieta inicial, así como en el momento de fractura inestable. A menudo dicha ident ificación no es obvia debido a un pobre contraste v isual de las superficies fracturadas. La circona estabilizada co n 3% molar de itria (3Y-TZP) es una cerámica biocom patible con buenas propiedades mecánicas que la hacen interesan te para su utilización en prótesis dentales y cabez as femorales. Adicionalmente, la...

17. Determination of the intrinsic fracture toughness from COD analysis of indentation cracks in spark plasma sintered 3Y-TZP reinforced with MWCNT - García Marro, Fernando; Chintapalli, Ravi Kiran; Mestra Rodríguez, Álvaro Miguel; Anglada Gomila, Marcos Juan
Postprint (published version)

18. Graphene-induced crystallinity of bisphenol A polycarbonate in the presence of supercritical carbon dioxide - Gedler, Gabriel; Sousa Pais Antunes, Marcelo de; Velasco Perero, José Ignacio
Changes in the crystallinity of polycarbonate (PC) induced by the simultaneous presence of 0.5 wt% graphene nanoplatelets (GnP) and supercritical carbon dioxide (sc-CO2) were examined by means of Raman spectroscopy, WAXS, SAXS and DSC. Composites were prepared by melt-mixing, compression-molding and dissolving sc-CO2 at high pressure and temperature. It was found that dissolved CO2 induced the formation of an ordered non-crystalline phase in PC during slow cooling under pressure. A fast depressurization and cooling did not cause such an effect in the resultant foams. GnP induced a higher crystallinity in PC, especially when combined with sc-CO2, even during fast depressurization...

19. Graphene-induced crystallinity of bisphenol A polycarbonate in the presence of supercritical carbon dioxide - Gedler, Gabriel; Sousa Pais Antunes, Marcelo de; Velasco Perero, José Ignacio
Changes in the crystallinity of polycarbonate (PC) induced by the simultaneous presence of 0.5 wt% graphene nanoplatelets (GnP) and supercritical carbon dioxide (sc-CO2) were examined by means of Raman spectroscopy, WAXS, SAXS and DSC. Composites were prepared by melt-mixing, compression-molding and dissolving sc-CO2 at high pressure and temperature. It was found that dissolved CO2 induced the formation of an ordered non-crystalline phase in PC during slow cooling under pressure. A fast depressurization and cooling did not cause such an effect in the resultant foams. GnP induced a higher crystallinity in PC, especially when combined with sc-CO2, even during fast depressurization...

20. Contact damage in artificially aged 3Y-TZP - Armas Sancho, Zamir de; Mestra Rodríguez, Álvaro Miguel; Jiménez Piqué, Emilio; Anglada Gomila, Marcos Juan
Tetragonal zirconia polycrystals doped with 3% mol of yttria (3Y - TZP) are increasingly employed as implants in the human body, because they are biocompatible and have relatively high strength and fracture toughness. These properties are related to the small submicrometer grain size and to the operation of a toughening mechanism around cracks which is referred to as phase tra nsformation toughening. Another important feature of 3Y - TZP is the phenomenon of low temperature degradation (LTD) that takes place in contact with water at temperatures in an interval around 250 ºC. Water activates t - m transformation at the surface and pr ogresses inside the body producing a t - m surface transformed layer. As a result, roughness and microcracking are produced in...

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