UPCommons - E-prints UPC Universitat Politècnica de Catalunya
(51.501 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 276
1.
Novel polycarbonate-graphene nanocomposite foams prepared by CO2 dissolution - Gedler, Gabriel; Sousa Pais Antunes, Marcelo de; Redondo Realinho, Vera Cristina de; Velasco Perero, José Ignacio
Polycarbonate foams reinforced with 0,5 wt% of graphene were obtained by firstly melt-mixing the polycarbonate and graphene in an internal mixer, compression-moulding the melt-compounded grinded material and lastly dissolving CO2 inside a high pressure vessel. The CO2 desorption behaviour in the unfilled polycarbonate and nanocomposite was studied in terms of the CO2 saturation concentration and desorption diffusion coefficient, with the graphene-filled nanocomposite displaying a higher CO2 loss rate when compared to the neat polycarbonate. The cellular structure of the foams was found to be highly dependent on the saturation/foaming temperature, with smaller cell sizes being obtained with decreasing the temperature....
2.
Influence of foaming process on the structure-properties relationship of foamed LDPE/silica nanocomposites - Saiz Arroyo, Cristina; Rodríguez Pérez, Miguel Ángel; Velasco Perero, José Ignacio; Saja, José Antonio de
In this paper LDPE/silica nanocomposites are foamed by two different processes. First one is the pressure quench method which is based on the use of a physical blowing agent and second one is the improved compression moulding technique. As the latter process uses a chemical blowing agent, both types of foamed nanocomposites will provide very useful information about the relationship between foaming process-microstructure and macroscopic properties. Results have revealed how silica nanoparticles are able to act as nucleating sites during foaming step in both processes; however, the optimum amount of particles strongly depends on the foaming route. Thermal and mechanical...
3.
Multifunctional nanocomposite foams based on polypropylene with carbon nanofillers - Sousa Pais Antunes, Marcelo de; Gedler, Gabriel; Velasco Perero, José Ignacio
This work considers the preparation and characterization of polypropylene foams with
variable concentrations of graphene and carbon nanofibres, focussing on the influence
of the foaming process and the nanofillers on the microstructural and dynamic-mechanical-
thermal properties of the foams. Great differences were found in terms of foam
morphology depending on the type of foaming process, with foams prepared by physical
foaming showing a vertically deformed cell structure, while chemical foams presented
an isotropic-like cellular structure. The addition of graphene resulted in foams with
higher cell densities and more uniform cellular structures when compared to the ones
with nanofibres. All these considerations are of extreme importance, as some of
the...
4.
Friction coefficients and wear rates of different orthodontic archwires in artificial saliva - Alfonso, M.V.; Espinar, Eduardo; Llamas, José María; Rupérez de Gracia, Elisa; Manero Planella, José María; Barrera, J.M; Solano, E.; Gil Mur, Francisco Javier
The aim of this paper is to analyze the influence
of the nature of the orthodontic archwires on the friction
coefficient and wear rate against materials used commonly as
brackets (Ti–6Al–4V and 316L Stainless Steel). The mate-
rials selected as orthodontic archwires were ASI304 stainless
steel, NiTi, Ti, TiMo and NiTiCu. The array archwire’s
materials selected presented very similar roughness but
different hardness. Materials were chosen from lower and
higher hardness degrees than that of the brackets. Wear tests
were carried out at in artificial saliva at 37
C. Results show a
linear relationship between the hardness of the materials and
the friction coefficients. The material that showed lower
wear rate was the...
5.
Biphasic calcium sulfate dihydrate/iron-modified alpha-tricalcium phosphate bone cement for spinal applications : in vitro study - Vlad, María Daniela; Valle Mendoza, Luis Javier del; Poeata, I.; López López, José; Torres Cámara, Ricardo; Barraco Serra, Marc; Fernández Aguado, Enrique
In this study, the cytocompatibility of new ‘iron-modified/alpha-tricalcium phosphate
(IM/α-TCP) and calcium sulfate dihydrate (CSD)’ bone cement (IM/α-TCP/CSD-BC)
intended for spinal applications has been approached. The objective was to investigate by direct-contact osteoblast-like cell cultures (from 1 to 14 days) the in vitro cell adhesion, proliferation, morphology and cytoskeleton organization of MG-63 cells seeded onto the new cements. The results were as follows: (a) quantitative MTT-assay and scanning electron microscopy (SEM) showed that cell adhesion, proliferation and viability were not affected with time by the presence of iron in the cements; (b) double immunofluorescent labeling of F-actin and α-tubulin showed a dynamic...
6.
Osteogenic biphasic calcium sulphate dihydrate/iron-modified alpha-tricalcium phosphate bone cement for spinal applications : in vivo study - Vlad, María Daniela; Sindilar, E.V.; Mariñoso, Maria Lluïsa; Poeata, I.; Torres Cámara, Ricardo; López López, José; Barraco Serra, Marc; Fernández Aguado, Enrique
In this study, the biocompatibility and the osteogenic features of a new iron-modified α-tricalcium phosphate (IM/α-TCP) and calcium sulphate dihydrate (CSD) biphasic cement (IM/α-TCP/CSD-BC) have been investigated in terms of the in vivo cement resorption, bone tissue formation and host tissue response on sheep animal model. Histological evaluation performed on undecalcified cement–bone specimens assessed the in vivo behaviour. It has been shown that the new IM/α-TCP/CSD-BC has the ability to produce firm bone binding in vivo (i.e. bioactivity). Qualitative histology proved cement biocompatibility, osteoconduction and favourable resorption, mainly through a macrophage-mediated mechanism. The results showed that the new cements have...
7.
Structure-property evaluation of trisilanolphenyl POSS®/polysulfone composites as a guide to POSS melt blending - Milliman, Henry; Sánchez Soto, Miguel; Arostegui, Asier; Schiraldi, David A.
A series of polysulfone/phenyl trisilanol
POSS nanocomposites were produced by melt blending by
twin screw batch mixing. These materials were then injec-
tion molded, and their thermal, mechanical, and morpho-
logical properties were tested. The tensile properties of
polysulfone were moderately compromised by the addition
of phenyl TPOSS, because of the formation of large (
1
l
m)
voided POSS aggregates. These domains however did cause
the improvement of the impact resistance of the composites
as described by the mechanism of crack pinning and bow-
ing. Flexural properties remained essentially unchanged,
which is attributed to the formation of an aggregate free-
skin layer, which formed in the injection molded parts. Thermal behavior of the composites...
8.
High-resolution PLA-based composite scaffolds via 3-D printing technology - Serra, Tiziano; Planell Estany, Josep Anton; Navarro Toro, Melba Eugenia
Fabrication of new biodegradable scaffolds that guide and stimulate tissue regeneration is still a major issue in tissue engineering approaches. Scaffolds that possess adequate biodegradability, pore size, interconnectivity, bioactivity and mechanical properties in accordance with the injured tissue are required. This work aimed to develop and characterize three-dimensional (3-D) scaffolds that fulfill the aforementioned requirements. For this, a nozzle-based rapid prototyping system was used to combine polylactic acid and a bioactive CaP glass to fabricate 3-D biodegradable scaffolds with two patterns (orthogonal and displaced double layer). Scanning electron microscopy and micro-computer tomography showed that 3-D scaffolds had completely interconnected porosity,...
9.
Modular polylactic acid microparticle-based scaffolds prepared via microfluidic emulsion/solvent displacement process: Fabrication, characterization, and in vitro mesenchymal stem cells interaction study - Salerno, Aurelio; Levato, R.; Mateos Timoneda, Miguel Angel; Engel López, Elisabeth; Netti, Paolo Antonio; Planell Estany, Josep Anton
The present study reports a novel approach for the
design and fabrication of polylactic acid (PLA) microparticle-
based scaffolds with microstructural properties suitable for
bone and cartilage regeneration. Macroporous PLA scaffolds
with controlled shape were fabricated by means of a semicon-
tinuous process involving (1) microfluidic emulsification of a
PLA/ethyl lactate solution (5% w/v) in a span 80/paraffin oil so-
lution (3% v/v) followed by (2) particles coagulation/assembly
in an acetone/water solution for the development of a continu-
ous matrix. Porous scaffolds prepared from particles with
monomodal or bimodal size distribution, overall porosity
ranges from 93 to 96%, interparticles porosity from 41 to 54%,
and static compression moduli from 0.3 to 1.4...
11.
The role of notch sharpening on the J-fracture toughness of thermoplastic polymers - Salazar, Alicia; Rodríguez, Jesús; Martínez Benasat, Antonio
The effect of the notch sharpening on the fracture toughness obtained under Elastic–Plastic Fracture Mechanics (EPFMs) approach has been analyzed in two different types of thermoplastic polymers, a semicrystalline multi-phase ethylene–propylene block copolymer and an amorphous polycarbonate. The samples for fracture characterization were sharpened using a steel razor blade and the femtosecond laser ablation technique. Both notching techniques gave rise to the very same size of crack tip radii, 1–2 μm. For all the materials under study, the fracture toughness values of the specimens sharpened through femtosecond laser ablation were lower than those measured on samples sharpened using a steel...
13.
Hot deformation activation energy (QHW) of austenitic Fe-22Mn-1.5Al-1.5Si-0.4C TWIP steels microalloyed with Nb, V, and Ti - Reyes Calderón, F.; Mejía Granados, Ignacio; Cabrera Marrero, José M.
The activation energy for hot deformation (
Q
HW
) of high-Mn microalloyed TWIP steels was determined
from experimental uniaxial hot compression curves. The presence of microalloying elements such as
Nb, V, and Ti, increases the
Q
HW
value from 366 in the non-microalloyed one to 446 kJ/mol in the
V-microalloyed TWIP steel. This change represents an increase from 16% up to 22% of
Q
HW
values.
14.
Effect of microalloying elements (Nb, V and Ti) on the hot flow behavior of high-Mn austenitic twinning induced plasticity (TWIP) steel - Reyes Calderón, F.; Mejía Granados, Ignacio; Boulaajaj, A.; Cabrera Marrero, José M.
This research work studies the effect of microalloying elements such as Nb, V and Ti on the hot flow
behavior of high-Mn austenitic TWIP steel. For this purpose, isothermal uniaxial hot compression tests
were carried out at three temperatures (900, 1000 and 1100
1
C) and four constant strain rates (10
1
,
10
2
,10
3
and 10
4
s
1
). Experimental results revealed that hot flow curves of microalloyed TWIP
steels show single peak curves for all test conditions. Results are discussed in terms of the peak stress
(
s
p
) and peak strain (
e
p
) and its dependence on the strain rate (
_
e
) and temperature. The addition of
microalloying elements such as Nb, V and Ti in...
15.
Determination of the critical parameters for the onset of dynamic recrystallization (DRX) in advanced ultrahigh strength steels (A-UHSS) microalloyed with boron - Altamirano Guerrero, Gerardo; Mejía Granados, Ignacio; Cabrera Marrero, José M.
In this research work, the double differentiation mathematical method was used to identify more accurately the criti-
cal stress
ሺ
ߪ
)
and critical strain
ሺ
ߝ
)
associated with the onset of dynamic recrystallization (DRX), which is based on
changes of the strain hardening rate
)ߝ߲/ߪ߲ ൌ ߠሺ
as a function of the flow stress (Poliak and Jonas method, simplified by
Najafizadeh and Jonas). For this purpose, a low carbon advanced ultra-high strength steel (A-UHSS) microalloyed with
different amounts of boron (14, 33, 82, 126 and 214 ppm) was deformed by uniaxial hot-compression tests at high tempe-
ratures
1100 ݀݊ܽ ሺ950,1000,1050
°
)ܥ
and constant true strain rates
ሺ
10
ିଷ
,10
ିଶ
10 ݀݊ܽ
ିଵ
ݏ
ିଵ
)
. Results indicate that
both
ߪ
and
ߝ
increase with decreasing deformation temperature and in
creasing...
16.
Influence of the injection-molding parameters on the cellular structure and thermo-mechanical properties of ethylene-propylene block copolymer foams - Gómez Gómez, Jaime Francisco; Arencón Osuna, David; Sánchez Soto, Miguel; Martínez Benasat, Antonio
Microcellular injection-molding technology is capable of
producing lightweight polymeric products. The foam morphology is determined
by the injection-molding parameters, and it has been observed that depending on
the parameter variations, the cell structure may exhibit substantial morphological
differences through the entire section along the melt flow direction of the injected part. The effects of varying injection-molding parameters on foam morphology
and thermal mechanical properties of a multiphase ethylene-propylene block
copolymer (EPBC) were tested on 5-mm plaque specimens using a constant
temperature profile. It has been found that injection speed does not have a
significant effect on the thermal-mechanical properties of the foam, whereas shot
volume and mold temperature do...
17.
On the onset of dynamic recrystallization in steels - Varela Castro, Gonzalo; Cabrera Marrero, José M.; Prado Pozuelo, José Manuel
The knowledge of the flow behavior of metallic all
oys subjected to hot forming
operations is of particular interest for designers
and engineers in the practice of industrial forming
processes simulations (i.e. rolling mill). Nowadays
dynamic recrystallization (DRX) is recognized
as one of the most relevant and meaningful mechanis
ms available for the control of microstructure.
This mechanism occurs during hot forming operations
over a wide range of metals and alloys and it
is known to be as a powerful tool which can be used
to the control of the microstructure and
properties of alloys. Therefore is important to kno
w, particularly in low stacking fault energy (SFE)
materials, the precise time for which...
18.
Equal channel angular pressing of Cu-Al bimetallic rods - Llorca Isern, Nuria; Escobar, Ana Maria; Roca, Antoni; Cabrera Marrero, José M.
Coextrusion and corolling are the major processes
to produce bimetallic rods, tubes and
wires, the objective being to perform clad metals,
bimetallic joints or seals. The aim of the present
work is to produce bimetallic rods showing an ultra
fine grained microstructure with enhanced
properties. Bimetallic Cu-Al rods were deformed by
equal channel angular pressing (ECAP) in
order to study their microstructure. ECAP is an int
eresting process for producing bulk materials
with refined microstructure and, consequently, chan
ges in physical, chemical and mechanical
properties can be observed. Higher shear strength a
nd dimensional stability are among the
advantages of this process. A comparative experimen
tal study of pure commercial copper with
cylindrical inner aluminium rods...
19.
Comportamiento termomecánico de un acero microaleado al Nb-V - Cartaya, E. A.; Varela, G.; Cabrera Marrero, José M.; Prado Pozuelo, José Manuel
Empleando ensayos de compresión simple en ca-
liente y relajación de tensiones después de la de
-
formación en un dilatómetro modelo DIL805T, se
obtuvieron las curvas de fluencia y relajación de
dos aceros, el primero de ellos al C – Mn y otro HS-
LA con idéntica composición química base, micro-
aleado con Nb – V.
Los ensayos de compresión simple fueron efectua-
dos a temperaturas en el rango austenítico, desde
900 – 1.200 ºC y velocidades de deformación de
0.001, 0.01, 0.1, 1 y 10 s
-
1
. Se obtuvieron las curvas de
fluencia para las diferentes condiciones, permitien-
do el estudio del efecto de los elementos microale-
antes sobre la recristalización dinámica y...
20.
Tomography of indentation cracks in feldspathic dental porcelain on zirconia - Rueda Arango, Astrid Oasis; Seuba, Jordi; Anglada Gomila, Marcos Juan; Jiménez Piqué, Emilio
Objectives
The objective of this work is to study the crack produced by spherical and sharp indentation on veneering feldspathic dental porcelain in order to understand the morphology of the cracks in the surface and beneath the indentation using a tomographic technique. The geometry of cracks produced under contact loading are directly related to the structural integrity and reliability of dental prosthesis.
Methods
Monotonic Hertzian contact loading and nanoindentation tests were performed on feldspathic porcelain (VITA-VM9) coatings. Residual imprints and the cracks produced by the indentations were characterized by 3-dimensional reconstruction using focused ion beam tomography.
Results
Under nanoindentation, the propagating crack deflects due to...
1.
