Journals
Authors:
Bikuna-Izagirre, M.; Aldazabal, J; Extramiana, L.; et al.
Journal:
ACS BIOMATERIALS SCIENCE & ENGINEERING
ISSN:
2373-9878
Year:
2023
Vol.:
9
N°:
11
pp.
6333 - 6344
Primary open-angle glaucoma is characterized by the progressive degeneration of the optic nerve, with the high intraocular pressure (IOP) being one of the main risk factors. The human trabecular meshwork (HTM), specifically the juxtacanalicular tissue (JCT), is responsible for placing resistance to the aqueous humor (AH) outflow and the resulting IOP control. Currently, the lack of a proper in vitro JCT model and the complexity of three-dimensional models impede advances in understanding the relationship between AH outflow and HTM degeneration. Therefore, we design an in vitro JCT model using a polycaprolactone (PCL) nanofibrous scaffold, which supports cells to recapitulate the functional JCT morphology and allow the study of outflow physiology. Mechanical and morphological characterizations of the electrospun membranes were performed, and human trabecular meshwork cells were seeded over the scaffolds. The engineered JCT was characterized by scanning electron microscopy, quantitative real-time polymerase chain reaction, and immunochemistry assays staining HTM cell markers and proteins. A pressure-sensitive perfusion system was constructed and used for the investigation of the outflow facility of the polymeric scaffold treated with dexamethasone (a glucocorticoid) and netarsudil (a novel IOP lowering the rho inhibitor). Cells in the in vitro model exhibited an HTM-like morphology, expression of myocilin, fibronectin, and collagen IV, genetic expression, outflow characteristics, and drug responsiveness. Altogether, the present work develops an in vitro JCT model to better understand HTM cell biology and the relationship between the AH outflow and the HTM and allow further drug screening of pharmacological agents that affect the trabecular outflow facility.
Authors:
Paredes, J; Cortizo-Lacalle, D.; Imaz, A.; et al.
Journal:
SCIENTIFIC REPORTS
ISSN:
2045-2322
Year:
2022
Vol.:
12
N°:
1
pp.
3898
Mechanical characterization supposes a key step in the development of cultured meat to help mimicking the sensorial properties of already existing commercial products based on traditional meat. This work presents two well stablished methods that can help studying cultured meat mechanical characteristics: texture profile analysis (double compression test) and rheology. These techniques provide data about the elastic and viscous behaviour of the samples but also values about other texture characteristics such as springiness, cohesiveness, chewiness and resilience. In this work, we present a comparison of cultured meat-based samples with commercial of the shelf common meat products (sausage, turkey and chicken breast). Results show that both Young¿s and Shear modulus in the cultured meat samples can be compared to commercial products in order to understand its properties. The texture characteristics for the cultured meat studied, show values within the range of commercial products. These results demonstrate the applicability of this methodology for the adjustment of mechanical properties of cultured meat products
Journal:
BIOMACROMOLECULES
ISSN:
1525-7797
Year:
2022
Vol.:
23
N°:
11
pp.
4629 - 4644
The co-administration of glial cell line-derived neurotrophic factor (GDNF) and mesenchymal stem cells (MSCs) in hydrogels (HGs) has emerged as a powerful strategy to enhance the efficient integration of transplanted cells in Parkinson's disease (PD). This strategy could be improved by controlling the cellular microenvironment and biomolecule release and better mimicking the complex properties of the brain tissue. Here, we develop and characterize a drug delivery system for brain repair where MSCs and GDNF are included in a nanoparticle-modified supramolecular guest-host HA HG. In this system, the nanoparticles act as both carriers for the GDNF and active physical crosslinkers of the HG. The multifunctional HG is mechanically compatible with brain tissue and easily injectable. It also protects GDNF from degradation and achieves its controlled release over time. The cytocompatibility studies show that the developed biomaterial provides a friendly environment for MSCs and presents good compatibility with PC12 cells. Finally, using RNA-sequencing (RNA-seq), we investigated how the three-dimensional (3D) environment, provided by the nanostructured HG, impacted the encapsulated cells. The transcriptome analysis supports the beneficial effect of including MSCs in the nanoreinforced HG. An enhancement in the anti-inflammatory effect of MSCs was observed, as well as a differentiation of the MSCs toward a neuron-like cell type. In summary, the suitable strength, excellent self healing properties, good biocompatibility, and ability to boost MSC regenerative potential make this nanoreinforced HG a good candidate for drug and cell administration to the brain.
Authors:
Chiesa-Estomba, C. M.; Hernaez-Moya, R.; Rodino, C.; et al.
Journal:
CARTILAGE
ISSN:
1947-6035
Year:
2022
Vol.:
13
N°:
4
pp.
105 - 118
Objective The surgical management of nasal septal defects due to perforations, malformations, congenital cartilage absence, traumatic defects, or tumors would benefit from availability of optimally matured septal cartilage substitutes. Here, we aimed to improve in vitro maturation of 3-dimensional (3D)-printed, cell-laden polycaprolactone (PCL)-based scaffolds and test their in vivo performance in a rabbit auricular cartilage model. Design Rabbit auricular chondrocytes were isolated, cultured, and seeded on 3D-printed PCL scaffolds. The scaffolds were cultured for 21 days in vitro under standard culture media and normoxia or in prochondrogenic and hypoxia conditions, respectively. Cell-laden scaffolds (as well as acellular controls) were implanted into perichondrium pockets of New Zealand white rabbit ears (N = 5 per group) and followed up for 12 weeks. At study end point, the tissue-engineered scaffolds were extracted and tested by histological, immunohistochemical, mechanical, and biochemical assays. Results Scaffolds previously matured in vitro under prochondrogenic hypoxic conditions showed superior mechanical properties as well as improved patterns of cartilage matrix deposition, chondrogenic gene expression (COL1A1, COL2A1, ACAN, SOX9, COL10A1), and proteoglycan production in vivo, compared with scaffolds cultured in standard conditions. Conclusions In vitro maturation of engineered cartilage scaffolds under prochondrogenic conditions that better mimic the in vivo environment may be beneficial to improve functional properties of the engineered grafts. The proposed maturation strategy may also be of use for other tissue-engineered constructs and may ultimately impact survival and integration of the grafts in the damaged tissue microenvironment.
Journal:
POLYMERS
ISSN:
2073-4360
Year:
2022
Vol.:
14
N°:
7
pp.
1311
The electrospinning of hybrid polymers is a versatile fabrication technique which takes advantage of the biological properties of natural polymers and the mechanical properties of synthetic polymers. However, the literature is scarce when it comes to comparisons of blends regarding coatings and the improvements offered thereby in terms of cellular performance. To address this, in the present study, nanofibrous electrospun scaffolds of polycaprolactone (PCL), their coating and their blend with gelatin were compared. The morphology of nanofibrous scaffolds was analyzed under field emission scanning electron microscopy (FE-SEM), indicating the influence of the presence of gelatin. The scaffolds were mechanically tested with tensile tests; PCL and PCL gelatin coated scaffolds showed higher elastic moduli than PCL/gelatin meshes. Viability of mouse embryonic fibroblasts (MEF) was evaluated by MTT assay, and cell proliferation on the scaffold was confirmed by fluorescence staining. The positive results of the MTT assay and cell growth indicated that the scaffolds of PCL/gelatin excelled in comparison to other scaffolds, and may serve as good candidates for tissue engineering applications.
Authors:
Garate, U.; Mardaras, E.; González, R.; et al.
Journal:
METALS
ISSN:
2075-4701
Year:
2022
Vol.:
12
N°:
6
pp.
1047
A multilayer laser-deposited lining of AISI 316L stainless steel makes a regular structural steel surface corrosion resistant in physiological media. Despite the application of single-layer stainless-steel linings being economically beneficial and allowing thinner surface modifications, dilution effects that modify the pitting resistance of the coating must be accounted for. In order to study the feasibility of employing single-layer coatings instead of multilayer coatings for corrosion protection in physiological media, a polarization testing back-to-back comparison was performed between laser-deposited AISI 316L monolayers on 42CrMo4 quenched and tempered steel and cold-rolled AISI 316L sheet in Dulbecco's Phosphate Buffer Solution at 36 degrees C. A higher dispersion in pitting resistance, ranging from 800 mV to 1200 mV, was found on the coated samples, whereas the cold-rolled material was more stable in the 1200 mV range. The resulting differences in corrosion rates and pitting potentials open the discussion on whether the chemical composition deviations on AISI 316L dilution layers are acceptable in terms of surface functionality in medical devices.
Journal:
REVISTA ESPAÑOLA DE MECÁNICA DE LA FRACTURA
ISSN:
2792-4246
Year:
2021
Vol.:
2
pp.
15 - 19
La determinación de la carga capaz de soportar un hueso se puede medir experimentalmente, en principio, mediante un ensayo de tracción convencional. Sin embargo, y dada la compleja geometría del hueso, así como las dificultades para su fijación en una máquina de tracción hace muy difícil la medida directa de la tensión de rotura mismo. Estas dificultades hacen que sea frecuente la determinación de las propiedades de dichos materiales mediante ensayos de flexión en 3 puntos.
Para determinar las propiedades mecánicas de los huesos mediante ensayos de flexión requiere del conocimiento no solo de los registros carga-desplazamiento obtenidos durante los ensayos sino también de la geometría de estos. En este trabajo se ha propone un método para determinar las propiedades mecánicas de huesos combinando ensayos mecánicos con técnicas de micro-tomografía computarizada. En este trabajo se ha realizado un ensayo bio-mecánico sobre un fémur de ratón del cual se conocía previamente su geometría. Dado el carácter frágil del hueso se ha supuesto un comportamiento elástico-lineal del mismo hasta el fallo. Una vez realizado el ensayo se ha determinado, a partir de la carga máxima alcanzada, la tensión máxima real que ha soportado empleando tanto las teorías clásicas de resistencia de materiales de vigas como técnicas de elementos finitos.
Como resultado de este trabajo se muestra la comparación entre los resultados obtenidos mediante la teoría de vigas, fácil de aplicar, y los modelos de elem
Authors:
Artola, G. (Autor de correspondencia); Aldazabal, J
Journal:
REVISTA DE METALURGIA
ISSN:
0034-8570
Year:
2021
Vol.:
57
N°:
3
pp.
e198
Different hydrogen-induced cracking patterns have been observed on two construction steels belonging to the same strength grade for mooring offshore structures, when tested in a Slow Strain Rate Tensile test (SSRT) condition. A scenario is hypothesized, in which this behaviour arises from differences in hydrogen trapping capacity between the two steels. A novel finite difference modelling approach is proposed to assess the plausibility of this hypothesis. The model is designed to resemble the effect of the diffusible and the trapped hydrogen in the nucleation and growth of cracks during SSRT, and consequently in life service. The effect of different hydrogen trapping capacities has been simulated employing the proposed stress-diffusion-strength model. A higher content in traps led to fewer cracks; while the absence of traps led to a higher number of cracks. These results fit with the hypothesis, as variations in trapping capacity lead to variations in the number of cracks.
Journal:
JOURNAL OF BONE AND MINERAL RESEARCH
ISSN:
0884-0431
Year:
2021
Vol.:
36
N°:
11
pp.
2203 - 2213
The remodeling of the extracellular matrix is a central function in endochondral ossification and bone homeostasis. During secondary fracture healing, vascular invasion and bone growth requires the removal of the cartilage intermediate and the coordinate action of the collagenase matrix metalloproteinase (MMP)-13, produced by hypertrophic chondrocytes, and the gelatinase MMP-9, produced by cells of hematopoietic lineage. Interfering with these MMP activities results in impaired fracture healing characterized by cartilage accumulation and delayed vascularization. MMP-10, Stromelysin 2, a matrix metalloproteinase with high homology to MMP-3 (Stromelysin 1), presents a wide range of putative substrates identified in vitro, but its targets and functions in vivo and especially during fracture healing and bone homeostasis are not well defined. Here, we investigated the role of MMP-10 through bone regeneration in C57BL/6 mice. During secondary fracture healing, MMP-10 is expressed by hematopoietic cells and its maximum expression peak is associated with cartilage resorption at 14 days post fracture (dpf). In accordance with this expression pattern, when Mmp10 is globally silenced, we observed an impaired fracture-healing phenotype at 14 dpf, characterized by delayed cartilage resorption and TRAP-positive cell accumulation. This phenotype can be rescued by a non-competitive transplant of wild-type bone marrow, indicating that MMP-10 functions are required only in cells of hematopoietic linage. In addition, we found that this phenotype is a consequence of reduced gelatinase activity and the lack of proMMP-9 processing in macrophages. Our data provide evidence of the in vivo function of MMP-10 during endochondral ossification and defines the macrophages as the lead cell population in cartilage removal and vascular invasion. (c) 2021 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).
Authors:
Stephens, M.; López-Linares, K.; Aldazabal, J; et al.
Journal:
SCIENTIFIC DATA
ISSN:
2052-4463
Year:
2021
Vol.:
8
N°:
1
pp.
240
The development of new effective and safer therapies for osteoporosis, in addition to improved diagnostic and prevention strategies, represents a serious need in the scientific community. Micro-CT image-based analyses in association with biomechanical testing have become pivotal tools in identifying osteoporosis in animal models by assessment of bone microarchitecture and resistance, as well as bone strength. Here, we describe a dataset of micro-CT scans and reconstructions of 15 whole femurs and biomechanical tests on contralateral femurs from C57BL/6JOlaHsd ovariectomized (OVX), resembling human post-menopausal osteoporosis, and sham operated (sham) female mice. Data provided for each mouse include: the acquisition images (.tiff), the reconstructed images (.bmp) and an.xls file containing the maximum attenuations for each reconstructed image. Biomechanical data include an.xls file with the recorded load-displacement, a movie with the filmed test and an.xls file collecting all biomechanical results.
Journal:
METALS
ISSN:
2075-4701
Year:
2020
Vol.:
10
N°:
12
pp.
1613
When steel components fail in service due to the intervention of hydrogen assisted cracking, discussion of the root cause arises. The failure is frequently blamed on component design, working conditions, the manufacturing process, or the raw material. This work studies the influence of quench and tempering and hot-dip galvanizing on the hydrogen embrittlement behavior of a high strength steel. Slow strain rate tensile testing has been employed to assess this influence. Two sets of specimens have been tested, both in air and immersed in synthetic seawater, at three process steps: in the delivery condition of the raw material, after heat treatment and after heat treatment plus hot-dip galvanizing. One of the specimen sets has been tested without further manipulation and the other set has been tested after applying a hydrogen effusion treatment. The outcome, for this case study, is that fracture risk issues only arise due to hydrogen re-embrittlement in wet service.
Journal:
METALS
ISSN:
2075-4701
Year:
2020
Vol.:
10
N°:
12
pp.
1649
Volume changes accompanying the plastic deformation at 300 K of nanocrystalline samples of alpha-Fe with a columnar grain structure possessing a < 1 (1) over bar0 > random fiber texture has been obtained from molecular dynamics (MD) simulations. The samples were strained in tension along the common axial direction of the columnar grains. After removal of the elastic volume change, the evolution of plastic volume strain was obtained. Small but non-negligible volume dilations or contractions are observed depending on size (samples of very small grain size show volume contraction). The rate of volume change is high during the first 10% plastic deformation and continues at a low pace thereafter; the first 10% deformation represents a transient in the stress-strain behavior too. The complex behavior observed is reasonably explained by the superposition of contributions from different plastically-induced structural changes to the mass density change: Mainly from changes of grain size, grain boundary structure, dislocation density and density of point-defects. The results are of interest for the development of crystal plasticity theories not restricted by the volume conserving assumption.
Journal:
INTERNATIONAL JOURNAL OF REFRACTORY METALS AND HARD MATERIALS
ISSN:
0958-0611
Year:
2018
Vol.:
70
pp.
45 - 55
Six suppliers from several countries were asked to furnish parallelepiped 10 × 30 × 80 mm3 samples of commercial purity tungsten machined from rolled plates in view of selecting a provider of tungsten bricks for the target of the European neutron spallation source, ESS, under construction in Lund (Sweden). Sample surfaces were to be ground and free from visible defects or oxidation. The material should be rolled after sintering. A minimum room temperature tensile strength of 600 MPa was specified. The samples were submitted to different blind mechanical tests, measurement of physical properties and structural observations in order to assess their suitability for the application. We present here a summary of their main measured properties. The dispersion of results is noteworthy; the exercise allowed to sort-out technically eligible candidates for the application.
Authors:
Artola, G. (Autor de correspondencia); Fernandez-Calvo, A. I.; Arredondo, A. ; et al.
Journal:
METALS
ISSN:
2075-4701
Hydrogen embrittlement susceptibility ratios calculated from slow strain rate tensile tests have been employed to study the response of three high-strength mooring steels in cold and warm synthetic seawater. The selected nominal testing temperatures have been 3 degrees C and 23 degrees C in order to resemble sea sites of offshore platform installation interest, such as the North Sea and the Gulf of Mexico, respectively. Three scenarios have been studied for each temperature: free corrosion, cathodic protection and overprotection. An improvement on the hydrogen embrittlement tendency of the steels has been observed when working in cold conditions. This provides a new insight on the relevance of the seawater temperature as a characteristic to be taken into account for mooring line design in terms of hydrogen embrittlement assessment.
Journal:
METALS
ISSN:
2075-4701
In general, the thermal cutting processes of steel plates are considered to have an influence on microstructures and residual stress distribution, which determines the mechanical properties and performance of cut edges. They also affect the quality of the surface cut edges, which further complicates the problem, because in most cases the surface is subjected to the largest stresses. This paper studies the influence of plasma cutting processes on the mechanical behavior of the cut edges of steel and presents the characterization results of straight plasma arc cut edges of steel plate grade S460M, 15 mm thick. The cutting conditions used are the standard ones for industrial plasma cutting. The metallography of CHAZ (Cut Heat Affected Zones) and hardness profiles versus distance from plasma cut edge surface are tested; the mechanical behavior of different CHAZ layers under the cut edge surface were obtained by testing of instrumented mini-tensile 300 mu m thick specimens. Also, the residual stress distribution in the CHAZ was measured by X-ray diffraction. The results for the mechanical properties, microstructure, hardness, and residual stresses are finally compared and discussed. This work concludes that the CHAZ resulting from the plasma cutting process is narrow (about 700 mu m) and homogeneous in plate thickness.
Journal:
MECCANICA
ISSN:
0025-6455
Year:
2016
Vol.:
51
N°:
2
pp.
401 - 413
The tensile elongation of an < 011 > oriented columnar nanocrystalline pure iron structure at a temperature of 300 K has been simulated by molecular dynamics (MD). The simulated sample contains 4.3 x 10(6) atoms and has been subject to free elongation along the < 011 > axis common to the grains. Periodic boundary conditions have been assumed. The grains are randomly oriented around their common < 011 > and the size of their cross section is about 10 nm. The stress-strain curve has been calculated up to 0.5 true strain. After elastic deformation and heterogeneous dislocation nucleation from the grain boundaries, it shows a peak stress of 8 GPa followed by a remarkably stable steady state with a flow stress of 5.15 GPa, where neither the crystallographic texture nor the grain structure show any important change despite the large plastic deformation imparted. Upon a strain reversal, a pronounced Bauschinger effect is then observed (-3.3 GPa compressive yield stress), followed by a hardening transient until the absolute level of the flow stress in compression reaches near the same value it had in tension when the unloading took place. The results of the MD simulation are discussed by comparison with experimental values of the strength and structural evolution of heavily drawn iron wires available in the bibliography.
Authors:
Andres, D.; Garcia, T.; Cicero, S.; et al.
Journal:
MATERIALS CHARACTERIZATION
ISSN:
1044-5803
Year:
2016
Vol.:
119
pp.
55 - 64
Thermal cutting processes introduce changes in the heat affected zone (HAZ), which can lead to a significant reduction of the service life of components. In order to assess their influence, different cutting processes have been analysed on a structural steel. The characterization of the reduced volumes of HAZ posed a major challenge, since conventional techniques require greater pieces of material. Alternative miniature techniques had to be applied, such as Small Punch tests and microhardness measurements, from which the material tensile properties and fracture toughness values have been obtained. Results show that oxyfuel HAZ exhibit minor alterations of the material, while plasma cutting seems to improve the material tensile properties and fracture toughness. Besides, the suitability and accuracy of the Small Punch technique for similar applications can be derived from this work, turning it into a promising candidate to perform integrity assessments of actual components. (C) 2016 Elsevier Inc All rights reserved.
Authors:
Cicero, S.; Garcia, T.; Alvarez, J.; et al.
Journal:
INTERNATIONAL JOURNAL OF FATIGUE
ISSN:
0142-1123
Year:
2016
Vol.:
87
pp.
50 - 58
When the fatigue behaviour of structural components containing holes is analysed, Eurocode 3 only considers the fatigue performance of drilled holes, limiting the use of thermal cutting processes to produce, for example, bolt holes. This paper studies the fatigue performance of structural steel plates containing thermally cut holes. The research covers three thermal cutting methods: the traditional one (oxy-fuel cutting) and two more modern processes (plasma and laser cutting). An experimental program composed of 150 fatigue specimens has been completed, combining four steels (S355M, 5460M, S690Q and S890Q), the three thermal cutting methods and two different thicknesses (15 mm and 25 mm). The S-N results obtained have been used to estimate the corresponding Eurocode 3 FAT classes, which have finally been validated by comparing them to additional experimental data found in the literature. (C) 2016 Elsevier Ltd. All rights reserved.
Authors:
Cicero, S. (Autor de correspondencia); García, T.; Alvarez; J.A.; et al.
Journal:
PROCEDIA ENGINEERING
ISSN:
1877-7058
Year:
2016
Vol.:
160
pp.
246 - 253
This paper evaluates the effect of different thermal cutting methods on the fatigue life of high strength steel S890Q. The investigation covers flame, plasma and laser cutting methodologies, and specimens with rectangular sections and cut straight edges. The experimental program is composed of 30 specimens that were conducted to failure by applying fatigue cycles with a stress ratio (R) of 0.1 in a high frequency testing machine. The resultant best-fit S-N curves have been compared, revealing a better performance for laser cut straight edges. Moreover, the corresponding Eurocode 3 FAT class has been derived for each of the three cutting methods, resulting in FAT160 in all cases. This suggests that the use Eurocode 3 FAT125, which is the fatigue class currently provided for flame cut straight edges, is an overconservative assumption for thermally cut straight edges in steel S890Q, regardless of the thermal cutting technique being used (flame, laser or plasma).
Authors:
Cicero, S.; Garcia, T.; Alvarez, J.; et al.
Journal:
ENGINEERING STRUCTURES
ISSN:
0141-0296
Year:
2016
Vol.:
111
pp.
152 - 161
Thermal cutting is commonly used in engineering practice to obtain the final shape of structural components, and includes oxy-fuel, plasma and laser cut technologies. The characteristics of the cut surface and the material transformations caused by these cutting methods determine the corresponding fatigue behaviour. However, in the case of thermally cut straight edges, design codes, including the Eurocode 3, provide fatigue design curves for oxy-fuel cuts, whereas emergent technologies such as plasma and laser cutting are not associated to any design curve, limiting their use in many engineering applications. This paper analyses the effect of oxy-fuel cutting, plasma cutting and laser cutting on the fatigue behaviour of cut straight edges performed on structural steels S355M, S460M, S690Q and S890Q An experimental programme composed of 150 fatigue specimens has been completed, combining the four steels, the three thermal cutting methods and two different thicknesses (15 mm and 25 mm). The obtained S-N results have been used to estimate the corresponding Eurocode 3 FAT classes, which have been finally validated by comparing them to numerous experimental data found in the literature. (C) 2015 Elsevier Ltd. All rights reserved.
Authors:
Capdevila, C.; Aranda, M.; Rementeria, R.; et al.
Journal:
ACTA MATERIALIA
ISSN:
1359-6454
Year:
2016
Vol.:
107
pp.
27 - 37
The strengthening mechanism observed during ageing at temperatures of 435 and 475 degrees C in the oxide dispersion strengthened (ODS) Fe-Cr-Al-Ti system has been investigated. Atom probe tomography (APT) and high-resolution transmission electron microscopy (HRTEM) analyses determined that the alloy undergoes simultaneous precipitation of Cr-rich (alpha' phase) and nanoscale precipitation of TiAl-rich intermetallic particles (beta' phase). APT indicated that the composition of the intermetallic beta' phase is Fe2AlTi0.6Cr0.4, and the evolving composition of alpha' phase with ageing time was also determined. The results obtained from HRTEM analyses allow us to confirm that the beta' precipitates exhibit a cubic structure and hence their crystallography is related to the Heusler-type Fe2AlTi (L2(1)) structure. The strengthening could be explained on the basis of two hardening effects that occur simultaneously: the first is due to the alpha-alpha' phase separation through the modulus effect, and the second mechanism is due to the interaction of nanoscale beta' particles with dislocations. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Journal:
PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES
ISSN:
1364-503X
An assessment is made here of the role played by the micropolar continuum theory on the cracked Brazilian disc test used for determining rock fracture toughness. By analytically solving the corresponding mixed boundary-value problems and employing singular-perturbation arguments, we provide closed-form expressions for the energy release rate and the corresponding stress-intensity factors for both mode I and mode II loading. These theoretical results are augmented by a set of fracture toughness experiments on both sandstone and marble rocks. It is further shown that the morphology of the fracturing process in our centrally pre-cracked circular samples correlates very well with discrete element simulations.
Authors:
Garcia, T.; Cicero, S.; Ibañéz, F.T.; et al.
Journal:
PROCEDIA ENGINEERING
ISSN:
1877-7058
Year:
2015
Vol.:
133
pp.
590 - 602
Current fatigue codes only consider the fatigue performance of drilled and punched holes, limiting the use of thermal cutting processes to produce bolt holes. This paper studies the fatigue performance of structural steel S460 M plates containing thermally cut bolt holes. The research covers three thermal cutting methods: the traditional one (oxy-fuel cutting) and two more modern processes (plasma and laser cutting). Specimen geometry is defined by a rectangular cross section with a cut hole in the middle. All the specimens were conducted to failure by applying fatigue cycles, the stress ratio (R) being 0.1. The corresponding S-N curve and fatigue limit were obtained for each cutting method. Fatigue results have been compared with previous researches on fatigue performance of drilled and punched holes, and with the predictions provided by current fatigue standards, analyzing the possibility to extrapolate their S-N curves, focused on drilled and punched holes, to thermally cut holes.
Authors:
Pimentel, G.; Capdevila, C.; Bartolome, M.; et al.
Journal:
REVISTA DE METALURGIA
ISSN:
0034-8570
Year:
2012
Vol.:
48
N°:
4
pp.
303 - 316
Technologies and means for developing biomass plant with higher energy conversion efficiencies are essential in order to implement the commitment to renewable biomass energy generation. Advanced, indirect Combined Cycle Gas Turbine (CCGT) systems offer overall biomass energy conversion efficiencies of 45 % and above, compared with the 35 % efficiency of conventional biomass steam plant. However to attain this efficiency in CCGT operation it will be necessary to develop a heat exchanger capable of gas operating temperatures and pressures of around 1100 degrees C and 15-30 bar, respectively, for entry heating the gas turbine working fluid. ODS ferritic steels is the kind of advance material to deal with this challenge, however work to optimize the coarse grain microstructure to improve creep hoop strength needs to be done. In this sense, this paper reports the recrystallisation behaviour of PM 2000 oxide dispersion strengthened ferritic alloy which was cold deformed after hot-rolling and extrusion. The results can be interpreted if it is assumed that anything which makes the microstructure heterogeneous, stimulates recrystallisation. In this sense, larger strain gradients lead to more refined and more isotropic grain structures. The combination of these results with finite element modeling are used to interpret the role of residual shear stresses on the development of recrystallized grain structure.
Journal:
MATHEMATICS AND COMPUTERS IN SIMULATION
ISSN:
0378-4754
Year:
2011
Vol.:
81
N°:
11
pp.
2564 - 2580
Liquid-phase sintering (LPS) is a consolidation process for metallic and ceramic powders. At given temperature conditions, the process occurs with constant amount of liquid phase. However, the evolution of solid-particle shape is observed, namely, the rounding of particles and the growth of big particles at the expense of the small ones, which is known as Ostwald ripening. In this work, we propose a Monte Carlo (MC) model to simulate the microstructural evolution during LPS. The model considers the change of state of the discretising elements, namely voxels, of the system. The microstructural evolution proceeds accounting for both the geometrical characteristics of the particles, such as the number of solid neighbours, and the amount of solute contained in or surrounding a randomly chosen voxel. This has been implemented in terms of two probability distribution functions (PDFs). The diffusion of solute has also been considered by means of the implementation of a three-dimensional finite-difference algorithm. The diffusional MC model that we present is able to reproduce the Ostwald ripening behaviour and, in particular, results match the case in which the process is limited by the diffusion of the solute in the liquid phase. (C) 2011 IMACS. Published by Elsevier B.V. All rights reserved.
Journal:
JOURNAL OF PHYSICS: CONFERENCE SERIES (PRINT)
ISSN:
1742-6588
Year:
2010
Vol.:
252
N°:
1
pp.
012004
Scaffolds are porous biocompatible materials with suitable microarchitectures that are designed to allow for cell adhesion, growth and proliferation. They are used in combination with cells in regenerative medicine to promote tissue regeneration by means of a controlled deposition of natural extracellular matrix by the hosted cells therein. This healing process is in many cases accompanied by scaffold degradation up to its total disappearance when the scaffold is made of a biodegradable material.
This work presents a computational model that simulates the degradation of scaffolds. The model works with three-dimensional microstructures, which have been previously discretised into small cubic homogeneous elements, called voxels. The model simulates the evolution of the degradation of the scaffold using a Monte Carlo algorithm, which takes into account the curvature of the surface of the fibres.
The simulation results obtained in this study are in good agreement with empirical degradation measurements performed by mass loss on scaffolds after exposure to an etching alkaline solution.
Journal:
MATHEMATICS AND COMPUTERS IN SIMULATION
ISSN:
0378-4754
Year:
2010
Vol.:
80
N°:
7
pp.
1469 - 1486
Liquid-phase sintering (LPS) is an industrial process used to consolidate materials composed of two different kinds of metallic and/or ceramic powders. At constant temperature, the amount of the present liquid-phase is constant However, the shape of particles of solid phase changes over time In general, the rounding of particles and the growth of big particles at the expense of the small ones are observed This process is known as Ostwald ripening. In this work, we propose a Monte Carlo (MC) model to simulate the microstructural evolution during LPS The discretizing elements of the system. namely the voxels. change state between solid and liquid. according to previously defined melting and solidification probability distribution functions (PDFs) The generated PDFs take into account the geometrical characteristics of the system particles in terms of number of solid neighbours that surround a randomly chosen voxel The geometrical MC model that we present is able to reproduce the Ostwald ripening behaviour and, in particular, matches the case in which the process occurs limited by the attachment/detachment of the solid phase to/from the surface of the particle (C) 2009 IMACS Published by Elsevier B V All rights reserved.
Journal:
PHILOSOPHICAL MAGAZINE
ISSN:
1478-6435
Year:
2010
Vol.:
90
N°:
27-28
pp.
3743 - 3756
We present molecular dynamics (MD) simulations of the shear-coupled migration (SCM) behaviour of symmetrical tilt boundaries perturbed by the presence of nano-cracks or nano-precipitates lying on the boundary plane. The simulations have been performed for copper bicrystals at room temperature (300 K). The tilt boundary gets pinned by the crack tip or precipitates; shear-coupled migration occurs only ahead of the pinning points. Bulging of the tilt boundary reduces the shear stress on the boundary surface near the pinning points. In the case of cracks, the local deviation of the boundary from the crack plane close to the crack tip hinders mode II crack propagation; in fact, crack healing is observed in some cases. The applied stress grows until depinning of the boundary takes place by SCM bulging or by the combined action of SCM with another deformation mechanism (emission of dislocations from the pinning point vicinity, grain boundary sliding).
