Modeling of microstructure evolution of Ti6Al4V for Additive Manufacturing

AM processes are characterized by complex thermal cycles that have a deep influence on the microstructural transformations of the deposited alloy. In this work, a general model for the prediction of microstructure evolution during solid state transformations of Ti6Al4V is presented. Several formulations have been developed and employed for modeling phase transformations in other manufacturing processes and, particularly, in casting. The proposed model is mainly based on the combination and modification of some of these existing formulations, leading to a new overall model specifically dedicated to AM. The accuracy and suitability of the integrated model is enhanced, introducing new dedicated features. In fact the model is designed to deal with fast cooling and re-heating cycles typical of AM processes because: (a) it is able to consider incomplete transformations and varying initial content of phases and (b) it can take into account simultaneous transformations.The model is implemented in COMET, an in-house Finite Element (FE)-based framework for the solution of thermo-mechanical engineering problems. The validation of the microstructural model is performed by comparing the simulation results with the data available in the literature. The sensitivity of the model to the variation of material parameters is also discussed

A phenomenological model for the solidification of eutectic and hypoeutectic alloys including recalescence and undercooling

In this work, a novel phenomenological model is proposed to study the liquid-to-solid phase change of eutectic and hypoeutectic alloy compositions. The objective is to enhance the prediction capabilities of the solidification models based on a-priori definition of the solid fraction as a function of the temperature field. However, the use of models defined at the metallurgical level is avoided to minimize the number of material parameters required. This is of great industrial interest because, on the one hand, the classical models are not able to predict recalescence and undercooling phenomena, and, on the other hand, the complexity as well as the experimental campaign necessary to feed most of the microstructure models available in the literature make their calibration difficult and very dependent on the chemical composition and the treatment of the melt. Contrarily, the proposed model allows for an easy calibration by means of few parameters. These parameters can be easily extracted from the temperature curves recorded at the hot spot of the quick cup test, typically used in the differential thermal analysis (DTA) for the quality control of the melt just before pouring. The accuracy of the numerical results is assessed by matching the temperature curves obtained via DTA of eutectic and hypoeutectic alloys. Moreover, the model is validated in more complex casting experiments where the temperature is measured at different thermocouple locations and the metallurgical features such as grain size and nucleation density are obtained from an exhaustive micrography campaign. The remarkable agreement with the experimental evidence validates the predicting capabilities of the proposed model.Peer ReviewedPostprint (author's final draft

Estudio epidemiológico sobre la prevalencia de uso de medicinas alternativas y complementarias por la población general y un grupo de médicos y estudiantes de medicina de la Comunidad de Madrid

Gómez Gascón, Tomás, codir.La medicina complementaria y alternativa (CAM) tiene un uso creciente en los países occidentales durante los últimos 20 años, con cifras en población general entre el 30 y el 90%. En España no hay estudios de población sobre el uso de estas terapias en la población general, aunque algunos estudios sobre pacientes y otros factores indirectos indican una alta utilización. Objetivos. Estimar la prevalencia de utilización de CAM y productos alternativos por la población general y un grupo de médicos de plantilla, médicos residentes y estudiantes de Medicina de la Comunidad de Madrid, así como conocer sus características socioculturales, los problemas de salud y razones que motivaron el uso, el gasto estimado por paciente y sus opiniones acerca de las CAM. Material y métodos: Estudio transversal de prevalencia mediante encuesta autoadministrada a cuatro muestras aleatorias significativas: una de población general perteneciente a las once áreas de Atención Primaria de Madrid (n=897), otra de médicos de plantilla (n=324) y residentes (n=111) de dos hospitales y áreas de Atención Primaria, y la última de estudiantes de dos facultades y hospitales universitarios (n=45). Resultados. Se recibieron 288 cuestionarios de población general (porcentaje de respuesta del 14,4%), 165 de médicos de plantilla (51%), 96 de residentes (86,5%) y 45 estudiantes (100%), El 66% de la población general había consumido productos alternativos y un 56,3% habían utilizado CAM en alguna ocasión, fundamentalmente terapias de relajación y de masaje, por problemas músculo-esqueléticos y de salud mental. Más del 75% tuvo percepción de mejoría y alto grado de satisfacción. La principal razón por la que acudieron a CAM fue la búsqueda de mejoría no alcanzada con la medicina convencional. El consejo de familiares o conocidos fue el principal medio por el que conocieron las terapias, y más de la mitad habían gastado menos de 50 euros mensuales en terapias y productos. Más del 80% opinó que las CAM deberían incluirse en el sistema sanitario público y los profesionales sanitarios recibir formación en ellas. En el análisis multivariado ser mujer, pertenecer al Área 5 de Atención Primaria y haber visitado a sanitarios convencionales más de 9 veces en el último año fueron los factores independientes asociados al uso de CAM. Un 42,1% de los no usuarios de CAM había consumido productos alterntativos y el 83,5% acudiría a CAM en caso de necesidad. Respecto a los médicos y estudiantes, habían consumido productos alternativos entre el 25 y el 45%, y acudido a CAM entre el 16 y el 36%, por las mismas patologías y a las mismas terapias que la población general, y su percepción de mejoría y grado de satisfacción fueron elevados aunque en menor grado que la población general. El gasto mensual en CAM y el medio por el que conocieron las terapias fueron los mismos que la población general. Entre el 48% y el 85% opinaron que las CAM debían incluirse en el sistema sanitario público y los profesionales sanitarios debían formarse en ellas. Entre los no usuarios de CAM, entre un 40% y un 73% habían consumido productos alternativos y del 68% al 76% declararon que acudirían a CAM si lo necesitaran en algún momento de su vida. Al comparar las cuatros subpoblaciones, la población general acudía a CAM entre 2 y 4 veces más que el resto, y a más terapias, y consumía productos alternativos entre 2 y 3 veces más. Conclusiones. El consumo de CAM y productos alternativos entre la población general es elevado, y mayor que entre los médicos y estudiantes. En todos ellos el nivel de satisfacción con las CAM es elevado y un alto porcentaje considera adecuado incluirlas dentro del sistema sanitario público y en la formación de los profesionales sanitarios

A Phenomenological Model for the Solidification of Eutectic and Hypoeutectic Alloys Including Recalescence and Undercooling

In this work, a novel phenomenological model is proposed to study the liquid-to-solid phase change of eutectic and hypoeutectic alloy compositions. The objective is to enhance the prediction capabilities of the solidification models based on a-priori definition of the solid fraction as a function of the temperature field. However, the use of models defined at the metallurgical level is avoided to minimize the number of material parameters required. This is of great industrial interest because, on the one hand, the classical models are not able to predict recalescence and undercooling phenomena, and, on the other hand, the complexity as well as the experimental campaign necessary to feed most of the microstructure models available in the literature make their calibration difficult and very dependent on the chemical composition and the treatment of the melt. Contrarily, the proposed model allows for an easy calibration by means of few parameters. These parameters can be easily extracted from the temperature curves recorded at the hot spot of the quick cup test, typically used in the differential thermal analysis (DTA) for the quality control of the melt just before pouring. The accuracy of the numerical results is assessed by matching the temperature curves obtained via DTA of eutectic and hypoeutectic alloys. Moreover, the model is validated in more complex casting experiments where the temperature is measured at different thermocouple locations and the metallurgical features such as grain size and nucleation density are obtained from an exhaustive micrography campaign. The remarkable agreement with the experimental evidence validates the predicting capabilities of the proposed model

Numerical modelling of heat transfer and experimental validation in Powder-Bed Fusion with the Virtual Domain Approximation

Among metal additive manufacturing technologies, powder-bed fusion features very thin layers and rapid solidification rates, leading to long build jobs and a highly localized process. Many efforts are being devoted to accelerate simulation times for practical industrial applications. The new approach suggested here, the virtual domain approximation, is a physics-based rationale for spatial reduction of the domain in the thermal finite-element analysis at the part scale. Computational experiments address, among others, validation against a large physical experiment of 17.5 $\mathrm{[cm^3]}$ of deposited volume in 647 layers. For fast and automatic parameter estimation at such level of complexity, a high-performance computing framework is employed. It couples FEMPAR-AM, a specialized parallel finite-element software, with Dakota, for the parametric exploration. Compared to previous state-of-the-art, this formulation provides higher accuracy at the same computational cost. This sets the path to a fully virtualized model, considering an upwards-moving domain covering the last printed layers

Modeling of microstructure evolution of Ti6Al4V for additive manufacturing

AM processes are characterized by complex thermal cycles that have a deep influence on the microstructural transformations of the deposited alloy. In this work, a general model for the prediction of microstructure evolution during solid state transformations of Ti6Al4V is presented. Several formulations have been developed and employed for modeling phase transformations in other manufacturing processes and, particularly, in casting. The proposed model is mainly based on the combination and modification of some of these existing formulations, leading to a new overall model specifically dedicated to AM. The accuracy and suitability of the integrated model is enhanced, introducing new dedicated features. In fact the model is designed to deal with fast cooling and re-heating cycles typical of AM processes because: (a) it is able to consider incomplete transformations and varying initial content of phases and (b) it can take into account simultaneous transformations.The model is implemented in COMET, an in-house Finite Element (FE)-based framework for the solution of thermo-mechanical engineering problems. The validation of the microstructural model is performed by comparing the simulation results with the data available in the literature. The sensitivity of the model to the variation of material parameters is also discussed.Peer ReviewedPostprint (published version

Numerical modelling and experimental validation in Selective Laser Melting

In this work a finite-element framework for the numerical simulation of the heat transfer analysis of additive manufacturing processes by powder-bed technologies, such as Selective Laser Melting, is presented. These kind of technologies allow for a layer-by-layer metal deposition process to cost-effectively create, directly from a CAD model, complex functional parts such as turbine blades, fuel injectors, heat exchangers, medical implants, among others. The numerical model proposed accounts for different heat dissipation mechanisms through the surrounding environment and is supplemented by a finite-element activation strategy, based on the born-dead elements technique, to follow the growth of the geometry driven by the metal deposition process, in such a way that the same scanning pattern sent to the numerical control system of the AM machine is used. An experimental campaign has been carried out at the Monash Centre for Additive Manufacturing using an EOSINT-M280 machine where it was possible to fabricate different benchmark geometries, as well as to record the temperature measurements at different thermocouple locations. The experiment consisted in the simultaneous printing of two walls with a total deposition volume of 107 cm3 in 992 layers and about 33,500 s build time. A large number of numerical simulations have been carried out to calibrate the thermal FE framework in terms of the thermophysical properties of both solid and powder materials and suitable boundary conditions. Furthermore, the large size of the experiment motivated the investigation of two different model reduction strategies: exclusion of the powder-bed from the computational domain and simplified scanning strategies. All these methods are analysed in terms of accuracy, computational effort and suitable application

Ibero-American consensus on learning outcomes for the acquisition of competencies by medical students through clinical simulation.

post-print389 K

Riesgos y beneficios de la investigación científica

Toda investigación biomédica con participantes humanos debe ser revisada a priori por un comité reconocido de ética en investigación. El propósito del ensayo persiguió conocer y reflexionar sobre los riesgos y beneficios de la investigación, para que las investigaciones propuestas beneficien directamente a los participantes, a su comunidad local o a la sociedad en su conjunto

Covarianzas de las secciones eficaces homogeneizadas en dos grupos de energía para cálculos de difusión

Para la realización del ejercicio I-3 del benchmark de UAM se han utilizado diferentes modulos del sistema SCALE para la generación de secciones eficaces macroscópicas homogenizadas en dos grupos de energía. Se ha llevado a cabo un análisis de las matrices de covarianzas y correlaciones entre diferentes tipos de elementos combustibles y entre diferentes configuraciones