46 research outputs found

    El “humming” en turbinas de gas, causas, efectos, y soluciones industriales actuales

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    En este trabajo se examinan algunas de las características más importantes del “humming”, una inestabilidad de la combustión en turbinas de gas, y se estudian los sistemas de control activos y pasivos, que actuando sobre las causas de este fenómeno, buscan mitigar los efectos nocivos al funcionamiento y componentes de estos equipos. A través del análisis de un modelo fisicomatemático que relaciona oscilaciones acústicas con oscilaciones en la liberación de calor excitadas por perturbaciones de flujo y relación de mezcla, se identifican las causas de las inestabilidades de la combustión. Posteriormente, y tomando como caso de estudio las turbinas de gas para generación de energía, se demuestra la diversidad de problemas ocasionados por estos fenómenos. Para concluir, se analizan las soluciones industriales actuales a estos problemas desde su acción en las variables en juego.Facultad de Ingenierí

    Uniaxial-deformation behavior of ice Ih as described by the TIP4P/Ice and mW water models

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    Using molecular dynamics simulations, we assess the uniaxial deformation response of ice Ih as described by two popular water models, namely, the all-atom TIP4P/Ice potential and the coarse-grained mW model. In particular, we investigate the response to both tensile and compressive uniaxial deformations along the [0001] and [01̄10] crystallographic directions for a series of different temperatures. We classify the respective failure mechanisms and assess their sensitivity to strain rate and cell size. While the TIP4P/Ice model fails by either brittle cleavage under tension at low temperatures or large-scale amorphization/melting, the mW potential behaves in a much more ductile manner, displaying numerous cases in which stress relief involves the nucleation and subsequent activity of lattice dislocations. Indeed, the fact that mW behaves in such a malleable manner even at strain rates that are substantially higher than those applied in typical experiments indicates that the mW description of ice Ih is excessively ductile. One possible contribution to this enhanced malleability is the absence of explicit protons in the mW model, disregarding the fundamental asymmetry of the hydrogen bond that plays an important role in the nucleation and motion of lattice dislocations in ice Ih.Fil: Santos Flórez, Pedro Antonio. Universidade Estadual de Campinas; BrasilFil: Ruestes, Carlos Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza; Argentina. Universidad Nacional de Cuyo. Facultad de Ciencias Exactas y Naturales; ArgentinaFil: de Koning, Maurice. Universidade Estadual de Campinas; Brasi

    Nanoporous refractory metals

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    En la última década se ha incrementado notablemente el interés en estudiar metales nanoporosos. Estos materiales, también denominados espumas metálicas nanoporosas, presentan una alta relación superficie/volumen, que los posiciona en un lugar privilegiado para su uso en procesos de catálisis, y han permitido llevar a cabo desarrollos tales como los denominados "Surface chemistry-powered actuators" y biosensores, con el beneficio adicional de contar con propiedades mecánicas mejoradas por efectos de escala nanométrica. Debido a su estructura, los usos potenciales se extienden a paneles estructurales livianos y dispositivos para absorción de impacto. Todas las aplicaciones mencionadas imponen la necesidad de contar con materiales de alta integridad estructural, motivando el interés en una profunda caracterización de su comportamiento elástico y plástico. El reciente descubrimiento y perfeccionamiento de la técnica de "liquid metal dealloying" ha abierto las puertas a la fabricación de una variedad de metales nanoporosos de altísima relevancia en aplicaciones estructurales, incluyendo metales refractarios nanoporosos de estructuras bcc yhcp. Algunas aplicaciones potenciales de estas estructuras se encuentran en el área de biomateriales, componentes electrónicos y energía nuclear, temáticas de interés para la industria y organismos como el INTI, CNEA, CONAE, MinCyT, Fundación Argentina de Nanotecnología e INVAP S.E. El objetivo de este proyecto es generar nuevos conocimientos sobre el comportamiento mecánico de losmetales refractarios nanoporosos, utilizando un abordaje computacional. Se propone realizar ensayos simulados de compresión de micropilares y nanoindentación sobre tantalio nanoporoso y tungsteno nanoporoso. Los resultados de este proyecto contribuirán a una comprensión más global del comportamiento mecánico de los metales refractarios nanoporosos y a una mejor interpretación de los resultados experimentales, proponiendo nuevas leyes de escalamiento y brindando pautas para un uso racional de estos materiales para su aplicación como materiales en reactores de fusión, bioimplantes, y otros usos emergentes.Interest in nanoporous metals has increased notoriously on the last decade. These materials, also know as nanoporous metallic foams, have a high surface/volume ratio, making them particularly suitable for catalysis applications, and have enabled developments such as "Surface chemistry-powered actuators" and biosensors, with the additional benefit of having improved mechanical properties enabled by nanoscale effects. Due to their structure, potential applications extend to lightweight structural panels and shock-absortion devices. All the aforementioned applications require good mechanical properties, which motivates the interest on a deep characterization of its elastic and plastic behavior. The recent development of "liquid metal dealloying" opened the possibility of manufacturing a variety of nanoporous metals of the hightest technological relevance, including refractory metals. Some potential applications include biomaterials, electronic components and nuclear energy. Areas of interest for industry and organizations such as INTI, CNEA, CONAE, MinCyT, Fundación Argentina de Nanotecnología and INVAP S.E. The objective of this project is to generate new knowledge about the mechanical behavior of nanoporous refractory metals using computational studies. We propose to perform simulations of compression of micropillars as well as nanoindentation on nanoporous tantalum and tungsten. The results of this project will contribute to a better understanding of the mechanical behavior of these materials, to a better interpretation of experimental results, scaling laws and providing guidelines to a rational use of these materials in applications such as fusion reactors, bioimplants, and other emerging uses

    Atomistic Simulation of Nanoindentation of Ice Ih

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    Using molecular dynamics simulations, we study the nanoindentation response of the ice Ih basal surface using two popular water models, namely, the all-atom TIP4P/Ice potential and the coarse-grained mW model. In particular, we consider two markedly different temperatures at which a quasi-liquid layer (QLL) is or is not present. We discuss loading curves, hardness estimates, deformation mechanisms, and residual imprints, considering the effect of the QLL, indenter size, and penetration rate. At very low temperatures, in the absence of a QLL, both potentials produce similar loading curves and deformation mechanisms. Close to the melting temperature, however, important differences were found, including deviations in the QLL thickness and fraction as well as the presence of a competition between pressure-induced melting and recrystallization events. Nevertheless, both potentials exhibit similar deformation mechanisms and steady-state hardness estimates that are consistent with experimental data. In addition to contributing to the discussion regarding the interpretation of experimental AFM loading curves, the present results provide valuable information concerning the simulation of contact problems involving ice and the behavior of these two popular water models under such circumstances.Fil: Santos Flórez, Pedro Antonio. Universidade Estadual de Campinas; BrasilFil: Ruestes, Carlos Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Interdisciplinario de Ciencias Básicas. - Universidad Nacional de Cuyo. Instituto Interdisciplinario de Ciencias Básicas; ArgentinaFil: De Koning, Maurice. Universidade Estadual de Campinas; Brasi

    Nanoindentation tests of heavy-ion-irradiated Au foams - Molecular dynamics simulation

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    Irradiation by light ions may change the mechanical properties of nanofoams. Using molecular-dynamics simulation, we study the effect of irradiating a Au foam (porosity, 50%, and ligament diameter, 3 nm) with heavy ions: here, 10 keV Au ions up to a dose of 4 × 1016 m-2. We demonstrate that in consequence, the ligament morphology changes in the irradiated region, caused by local melting. The changes in mechanical properties are monitored by simulated nanoindentation tests. We find that the foam hardness is only around 1/3 of the hardness of a bulk Au crystal. Irradiation increases the hardness of the foam by around 10% in the central irradiated area. The plastic zone extends to only 1.5 ac, where ac denotes the contact radius; this value is unchanged under irradiation. The hardness increase after irradiation is attributed to two concurring effects. To begin with, irradiation induces melting and annealing of the ligaments, leading to their coarsening and alleviating surface stress, which in turn increases the dislocation nucleation threshold. In addition, irradiation introduces a stacking fault forest that acts as an obstacle to dislocation motion.Fil: Ruestes, Carlos Javier. Universidad Nacional de Cuyo. Facultad de Ciencias Exactas y Naturales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza; ArgentinaFil: Anders, Christian. University Kaiserslautern; AlemaniaFil: Bringa, Eduardo Marcial. Universidad de Mendoza; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza; ArgentinaFil: Urbassek, Herbert M.. University Kaiserslautern; Alemani

    Boosting materials science simulations by high performance computing

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    Ponencia presentada en el XXIII Congreso de Métodos Numéricos y sus Aplicaciones. La Plata, Argentina, del 7 al 10 de noviembre de 2017.Fil: Millán, Emmanuel Nicolás. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina.Fil: Millán, Emmanuel Nicolás. Universidad Nacional de Cuyo. Facultad de Ciencias Exactas y Naturales; Argentina.Fil: Ruestes, Carlos Javier. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina.Fil: Ruestes, Carlos Javier. Universidad Nacional de Cuyo. Facultad de Ciencias Exactas y Naturales; Argentina.Fil: Wolovick, Nicolás. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía, Física y Computación; Argentina.Fil: Bringa, Eduardo Marcial. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina.Fil: Bringa, Eduardo Marcial. Universidad Nacional de Cuyo. Facultad de Ciencias Exactas y Naturales; Argentina.Technology development is often limited by knowledge of materials engineering and manufacturing processes. This scenario spans across scales and disciplines, from aerospace engineering to MicroElectroMechanical Systems (MEMS) and NanoElectroMechanical Systems (NEMS). The mechanical response of materials is dictated by atomic/nanometric scale processes that can be explored by molecular dynamics (MD) simulations. In this work we employ atomistic simulations to prove indentation as a prototypical deformation process showing the advantage of High Performance Computing (HPC) implementations for speeding up research. Selecting the right HPC hardware for executing simulations is a process that usually involves testing different hardware architectures and software configurations. Currently, there are several alternatives, using HPC cluster facilities shared between several researchers, as provided by Universities or Government Institutions, owning a small cluster, acquiring a local workstation with a high-end microprocessor, and using accelerators such as Graphics Processing Units (GPU), Field Programmable Gate Arrays (FPGA), or Intel Many Integrated Cores (MIC). Given this broad set of alternatives, we run several benchmarks using various University HPC clusters, a former TOP500 cluster in a foreign computing center, two high-end workstations and several accelerators. A number of different metrics are proposed to compare the performance and aid in the selection of the best hardware architecture according to the needs and budget of researchers. Amongst several results, we find that the Titan X Pascal GPU has a ∼3 x speedup against 64 AMD Opteron CPU cores.https://cimec.org.ar/ojs/index.php/mc/article/view/5277Fil: Millán, Emmanuel Nicolás. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina.Fil: Millán, Emmanuel Nicolás. Universidad Nacional de Cuyo. Facultad de Ciencias Exactas y Naturales; Argentina.Fil: Ruestes, Carlos Javier. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina.Fil: Ruestes, Carlos Javier. Universidad Nacional de Cuyo. Facultad de Ciencias Exactas y Naturales; Argentina.Fil: Wolovick, Nicolás. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía, Física y Computación; Argentina.Fil: Bringa, Eduardo Marcial. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina.Fil: Bringa, Eduardo Marcial. Universidad Nacional de Cuyo. Facultad de Ciencias Exactas y Naturales; Argentina.Ciencias de la Computació

    Effect of subsurface voids on the nanoindentation of Fe crystals

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    Subsurface voids may strongly affect the response of materials to nanoindentation. We explore these effects for a bcc single-crystalline Fe sample using molecular dynamics simulation. Deformation occurs mainly by nucleation and propagation of dislocations. As dislocations impinge into the voids, these suffer a reduction in volume, consistent with mass transfer mechanisms. Our results show that voids act as highly efficient absorbers of dislocations, effectively limiting the extension of the plastic zone. Surprisingly, mechanical properties are marginally affected by the presence of voids in the range of sizes and spatial distributions tested, except for voids a few nanometers below the surface. Deformation twinning is observed as a transient effect in some cases; however, for voids close enough to the indentation area, no twinning was found.Fil: Hofer, Juan Andres. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; ArgentinaFil: Ruestes, Carlos Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Interdisciplinario de Ciencias Básicas. - Universidad Nacional de Cuyo. Instituto Interdisciplinario de Ciencias Básicas; Argentina. Universidad Nacional de Cuyo. Facultad de Ciencias Exactas y Naturales; ArgentinaFil: Bringa, Eduardo Marcial. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Universidad de Mendoza. Facultad de Ingeniería; Argentina. Universidad Mayor; ChileFil: Urbassek, Herbert M.. University Kaiserslautern; Alemani

    Micro-mechanical response of ultrafine grain and nanocrystalline tantalum

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    In order to investigate the effect of grain boundaries on the mechanical response in the micrometer and submicrometer levels, complementary experiments and molecular dynamics simulations were conducted on a model bcc metal, tantalum. Microscale pillar experiments (diameters of 1 and 2 μm) with a grain size of ~100-200 nm revealed a mechanical response characterized by a yield stress of ~1500 MPa. The hardening of the structure is reflected in the increase in the flow stress to 1700 MPa at a strain of ~0.35. Molecular dynamics simulations were conducted for nanocrystalline tantalum with grain sizes in the range of 20-50 nm and pillar diameters in the same range. The yield stress was approximately 6000 MPa for all specimens and the maximum of the stress-strain curves occurred at a strain of 0.07. Beyond that strain, the material softened because of its inability to store dislocations. The experimental results did not show a significant size dependence of yield stress on pillar diameter (equal to 1 and 2 um), which is attributed to the high ratio between pillar diameter and grain size (~10-20). This behavior is quite different from that in monocrystalline specimens where dislocation 'starvation' leads to a significant size dependence of strength. The ultrafine grains exhibit clear 'pancaking' upon being plastically deformed, with an increase in dislocation density. The plastic deformation is much more localized for the single crystals than for the nanocrystalline specimens, an observation made in both modeling and experiments. In the molecular dynamics simulations, the ratio of pillar diameter (20-50 nm) to grain size was in the range 0.2-2, and a much greater dependence of yield stress to pillar diameter was observed. A critical result from this work is the demonstration that the important parameter in establishing the overall deformation is the ratio between the grain size and pillar diameter; it governs the deformation mode, as well as surface sources and sinks, which are only important when the grain size is of the same order as the pillar diameter.Fil: Yang, Wen. University of California at San Diego; Estados UnidosFil: Ruestes, Carlos Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Interdisciplinario de Ciencias Básicas. - Universidad Nacional de Cuyo. Instituto Interdisciplinario de Ciencias Básicas; ArgentinaFil: Li, Zezhou. University of California at San Diego; Estados UnidosFil: Abad, Oscar Torrents. Leibniz Institute for New Materials; AlemaniaFil: Langdon, Terence G.. University of Southern California; Estados UnidosFil: Heiland, Birgit. Leibniz Institute for New Materials; AlemaniaFil: Koch, Marcus. Leibniz Institute for New Materials; AlemaniaFil: Arzt, Eduard. Leibniz Institute for New Materials; Alemania. Universitat Saarland; AlemaniaFil: Meyers, Marc A.. University of California at San Diego; Estados Unido

    A stochastic discrete slip approach to microplasticity: Application to submicron W pillars

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    A stochastic discrete slip approach is proposed to model plastic deformation in submicron domains. The model is applied to the study of submicron pillar () compression experiments on tungsten (W), a prototypical metal for applications under extreme conditions. Slip events are geometrically resolved in the specimen and considered as eigenstrain fields producing a displacement jump across a slip plane. This novel method includes several aspects of utmost importance to small-scale plasticity, i.e. source truncation effects, surface nucleation effects, starvation effects, slip localization and an inherently stochastic response. Implementation on an FFT-spectral solver results in an efficient computational 3-D framework. Simulations of submicron W pillars () under compression show that the method is capable of capturing salient features of sub-micron scale plasticity. These include the natural competition between pre-existing dislocations and surface nucleation of new dislocations. Our results predict distinctive flow stress power-law dependence exponents as well as a size-dependence of the strain-rate sensitivity exponent. The results are thoroughly compared with experimental literature.Fil: Ruestes, Carlos Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Interdisciplinario de Ciencias Básicas. - Universidad Nacional de Cuyo. Instituto Interdisciplinario de Ciencias Básicas; ArgentinaFil: Segurado, Javier. Universidad Politécnica de Madrid; Españ

    Deformation response of high entropy alloy nanowires

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    This paper reports atomistic simulation studies of tensile and compressive behavior of nanowires of a model quinary high entropy face-centered cubic (FCC) alloy. The simulations employ empirical interatomic potentials and use massively parallel molecular dynamics techniques at the atomistic level to study the deformation mechanisms. The studies consider pristine cylindrical nanowires oriented along various crystallographic directions. The focus is the role that local composition fluctuations in the random alloy plays in the deformation response. The deformation behavior observed for the complex random alloy is compared with a corresponding ‘‘average atom’’ material that has the same average properties but no local compositional fluctuations. In all cases, deformation is governed by dislocations emitted from the free surface. Twinning was also found, depending on the crystallographic orientation and loading mode. We show that for all orientations, the high entropy alloy (HEA) wires show the onset of plasticity at lower stress levels than the average atom material. However, after the onset of plasticity, the HEA presents a higher strength, mostly driven by the fact that the dislocations emitted from the surface do not glide as easily in the random alloy as they do in the average atom material.Fil: Ruestes, Carlos Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Interdisciplinario de Ciencias Básicas. - Universidad Nacional de Cuyo. Instituto Interdisciplinario de Ciencias Básicas; ArgentinaFil: Farkas, Diana. Virginia Tech University; Estados Unido
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