On the Micro-Mechanical Property Characterization and Bulk-Volume Behavior Prediction of Additively Manufactured 17-4 PH Stainless Steels

Selective laser melting is an additive manufacturing technology that opens the possibility to manufacture components with complex geometries that are difficult with traditional manufacturing techniques which could benefit engineering applications such as aviation or structural engineering. However, the lack of a reliable universal predictive model for selective laser melting components could impede the full implementation in industrial applications. Therefore, this dissertation investigates the mechanical behavior of selective laser melting 17-4 PH stainless steel under ultra-low cycle fatigue regime and propose a novel micro-mechanical based modeling using statistical and representative volume element. The first phase of this project examined the mechanical behavior of selective laser melting 17-4 PH stainless steel at macro-scale by tensile test and ultra-low cycle fatigue testing (Δ��/2 = 2%, 3% and 4%), and were compared to its wrought counterpart. Results showed that selective laser melting components underperform by 62% and 65%, compared to its wrought counterpart, when subjected to cyclic load with amplitudes of (Δ��/2 = 3% and 4%) respectively. Further examination in the fracture surface revealed the presence of voids within selective laser melting samples. This shows the detrimental effect that fabrication induced defects have over the fatigue life in selective laser melting. Also, Coffin-mason universal slope over predicts the performance of additively manufactured steel by 119% and 213% on strain amplitudes of 3% and 4%. Thus, a predictive model based on micro-mechanical testing is studied. The second part of this project describes a methodology to improve the micro-tensile sample fabrication throughput. This methodology consists in the pre-fabrication of micro-columns by photolithography and wet-etching. During wet-etching, excess of bulk material is removed, reducing the material re-deposition during the focused ion beam milling and easing the maneuverability of the grip by fabricating samples above bulk surface. Possible challenges during testing were commented on along recommendation on how to perform micro-tensile tests. Once the methodology was developed, selective laser melting 17-4 PH stainless steel was characterized via small scale mechanical testing such as nanoindentation, micro-compression and micro-tensile. An elastic modulus of 187.6 GPa was measured using nanoindendation with a Berkovich indenter. From the micro-compression, a yield stress of 759 MPa ± 207 MPa was measured. Also, a strain-hardening behavior was seen. An increase of 47% in the yield stress (1115 MPa) in micro-tensile test was seen, when compared to micro-compression. When micro- and macro- tensile test are compared, micro-tensile specimen shows an ultimate tensile strength of 1359 MPa, ~21% higher than the bulk specimen (1115 MPa). Also, the pronounced strain hardening behavior in macro-specimen was not shown during micro-specimen, suggesting different failure mechanisms. Lastly, this project proposes a framework for a predictive model based on micro-mechanical testing using statistical and representative volume elements. For this, a methodology was suggested, using representative volume element, to up-scale micro-mechanical properties. Then, using statistical volume elements, the effects of voids were studied. Although the model predicts mechanical behavior with low accuracy, suggestions as performing mechanical testing at the meso-scale and combining characterization techniques with micro-mechanical testing were done

On the Micro-Mechanical Property Characterization and Bulk-Volume Behavior Prediction of Additively Manufactured 17-4 PH Stainless Steels

Selective laser melting is an additive manufacturing technology that opens the possibility to manufacture components with complex geometries that are difficult with traditional manufacturing techniques which could benefit engineering applications such as aviation or structural engineering. However, the lack of a reliable universal predictive model for selective laser melting components could impede the full implementation in industrial applications. Therefore, this dissertation investigates the mechanical behavior of selective laser melting 17-4 PH stainless steel under ultra-low cycle fatigue regime and propose a novel micro-mechanical based modeling using statistical and representative volume element. The first phase of this project examined the mechanical behavior of selective laser melting 17-4 PH stainless steel at macro-scale by tensile test and ultra-low cycle fatigue testing (Δ��/2 = 2%, 3% and 4%), and were compared to its wrought counterpart. Results showed that selective laser melting components underperform by 62% and 65%, compared to its wrought counterpart, when subjected to cyclic load with amplitudes of (Δ��/2 = 3% and 4%) respectively. Further examination in the fracture surface revealed the presence of voids within selective laser melting samples. This shows the detrimental effect that fabrication induced defects have over the fatigue life in selective laser melting. Also, Coffin-mason universal slope over predicts the performance of additively manufactured steel by 119% and 213% on strain amplitudes of 3% and 4%. Thus, a predictive model based on micro-mechanical testing is studied. The second part of this project describes a methodology to improve the micro-tensile sample fabrication throughput. This methodology consists in the pre-fabrication of micro-columns by photolithography and wet-etching. During wet-etching, excess of bulk material is removed, reducing the material re-deposition during the focused ion beam milling and easing the maneuverability of the grip by fabricating samples above bulk surface. Possible challenges during testing were commented on along recommendation on how to perform micro-tensile tests. Once the methodology was developed, selective laser melting 17-4 PH stainless steel was characterized via small scale mechanical testing such as nanoindentation, micro-compression and micro-tensile. An elastic modulus of 187.6 GPa was measured using nanoindendation with a Berkovich indenter. From the micro-compression, a yield stress of 759 MPa ± 207 MPa was measured. Also, a strain-hardening behavior was seen. An increase of 47% in the yield stress (1115 MPa) in micro-tensile test was seen, when compared to micro-compression. When micro- and macro- tensile test are compared, micro-tensile specimen shows an ultimate tensile strength of 1359 MPa, ~21% higher than the bulk specimen (1115 MPa). Also, the pronounced strain hardening behavior in macro-specimen was not shown during micro-specimen, suggesting different failure mechanisms. Lastly, this project proposes a framework for a predictive model based on micro-mechanical testing using statistical and representative volume elements. For this, a methodology was suggested, using representative volume element, to up-scale micro-mechanical properties. Then, using statistical volume elements, the effects of voids were studied. Although the model predicts mechanical behavior with low accuracy, suggestions as performing mechanical testing at the meso-scale and combining characterization techniques with micro-mechanical testing were done

Optimisation of flow chemistry: tools and algorithms

The coupling of flow chemistry with automated laboratory equipment has become increasingly common and used to support the efficient manufacturing of chemicals. A variety of reactors and analytical techniques have been used in such configurations for investigating and optimising the processing conditions of different reactions. However, the integrated reactors used thus far have been constrained to single phase mixing, greatly limiting the scope of reactions for such studies. This thesis presents the development and integration of a millilitre-scale CSTR, the fReactor, that is able to process multiphase flows, thus broadening the range of reactions susceptible of being investigated in this way. Following a thorough review of the literature covering the uses of flow chemistry and lab-scale reactor technology, insights on the design of a temperature-controlled version of the fReactor with an accuracy of ±0.3 ºC capable of cutting waiting times 44% when compared to the previous reactor are given. A demonstration of its use is provided for which the product of a multiphasic reaction is analysed automatically under different reaction conditions according to a sampling plan. Metamodeling and cross-validation techniques are applied to these results, where single and multi-objective optimisations are carried out over the response surface models of different metrics to illustrate different trade-offs between them. The use of such techniques allowed reducing the error incurred by the common least squares polynomial fitting by over 12%. Additionally, a demonstration of the fReactor as a tool for synchrotron X-Ray Diffraction is also carried out by means of successfully assessing the change in polymorph caused by solvent switching, this being the first synchrotron experiment using this sort of device. The remainder of the thesis focuses on applying the same metamodeling and cross-validation techniques used previously, in the optimisation of the design of a miniaturised continuous oscillatory baffled reactor. However, rather than using these techniques with physical experimentation, they are used in conjunction with computational fluid dynamics. This reactor shows a better residence time distribution than its CSTR counterparts. Notably, the effect of the introduction of baffle offsetting in a plate design of the reactor is identified as a key parameter in giving a narrow residence time distribution and good mixing. Under this configuration it is possible to reduce the RTD variance by 45% and increase the mixing efficiency by 60% when compared to the best performing opposing baffles geometry

Bidirectional violence: a critical approach to Central American women

The central proposal of this paper is to approximate a theoretical model of women in criminal violence based on some Central American dynamics. Through process tracing, the stages of women as recipients of violence and women as vehicles of violence are raised. Indeed, the relationship between gender and criminality reveals the interaction between two fundamental facets: underground integration and criminal governance in the region. Underground and criminal integrations are found to be much more effective to perform because transaction costs between actors are lower, while, between states, by their own configuration, there are more limitations and robust integration costs due to variables such as sovereignty, politics, economy, and security. Based on the above, it should be mentioned that the reduction of violence against women does not lie in the increase in penalties, but in the effective functioning of justice operators. A reduction of such phenomenon must be based on greater agility of investigations and the strengthening of criminal policy, to minimize the capacity for action and coercion. On the other hand, the effectiveness of the policy seeks to increase persuasion against potential members of criminal networks to desist from their participation

The importance of mobile phone advertising

La publicidad, en su constante búsqueda de vías alternativas para evitar los saturados medios tradicionales, no puede perder de vista las posibilidades que le ofrece el teléfono móvil como medio de comunicación persuasiva. Con objeto de obtener el máximo rendimiento de estas innegables condiciones, hay que conocer cuáles son las líneas de explotación publicitaria que ofrecen mejores opciones para desarrollar acciones eficaces y entender cómo se ejecutan.Advertising, in its constant search for alternative ways to avoid saturated traditional media cannot lose sight of the possibilities offered by mobile phone as a means of persuasive communication. In order to get the most out of these undeniable conditions, we must know which advertising business lines offer better options to develop effective actions and understand how they run

Análisis del consumidor en redes sociales y su percepción de las marcas

The use of social networks has proliferated in recent years. Although it is a very recent phenomenon, there are more and more types of networks used for different purposes. This is a review of the results of different researches carried out around this social phenomenon in Spain. To introduce the context this study retrieves a historical retrospective from the origins of social networks in the US at the end of the last century until today. The analysis begins with the results of the IAB Spain research “Situation on Social Networks 2019”. The main conclusions are compared with those obtained from the research on social networks carried out by Publicis Media to understand consumer habits in this environment “Discovering Social Networks: Map of Consumption and use in Spain 2019”. This followed by a comparative analysis of the results of both research, focusing on Social Network trends and an in-depth study on the most popular social platforms in Spain: Youtube, Facebook, Instagram, WhatsApp, and Twitter. Although social networks are perceived as platforms for young people, there is a very high consumption in the profiles called “perennials”, which respond to a behavioral or attitudinal profile rather than a sociodemographic one. To conclude this reflection there is a focus on advertising in Social Networks, analyzing the perception of users and the behavior of brands as recorded in the “VII Observatory of Brands in Social Networks” published in 2019 by IAB Spain.El uso de las redes sociales ha proliferado en los últimos años. Aunque es un fenómeno social muy reciente cada vez hay más tipologías de redes que se utilizan con distintos fines. En este trabajo se realiza una revisión de los resultados de varias investigaciones realizadas en torno a este fenómeno social y, en particular, su situación en España. Para situar el contexto se recoge una retrospectiva histórica desde sus orígenes en Estados Unidos a finales del siglo pasado hasta la actualidad. El estudio comienza por una referencia sectorial del “Estudio Anual sobre Redes Sociales 2019” realizado por IAB Spain. Estos resultados se comparan con los obtenidos de la investigación sobre redes sociales realizada por Publicis Media para entender los hábitos del consumidor en este entorno “Descubriendo las Redes Sociales: Mapa de Consumo y uso en España 2019”. Se valoran los resultados de ambas investigaciones y se analizan las tendencias en el uso de las Redes Sociales con un estudio en profundidad sobre las plataformas sociales de mayor uso en España: Youtube, Facebook, Instagram, WhatsApp y Twitter. Aunque las redes sociales se perciben como plataformas dirigidas jóvenes, se demostrará cómo hay un consumo muy elevado en los perfiles denominados perenials, que responden a un perfil comportamental o actitudinal más que sociodemográfico. Para finalizar este análisis, se realiza un foco sobre la publicidad en Redes Sociales, analizando la percepción de los usuarios y el comportamiento de las marcas según se recoge en el “VII Observatorio de las Marcas en Redes Sociales” publicado en 2019 por IAB Spain

Nutrición en ancianos físicamente activos

Objetivo: El envejecimiento involucra diversos cambios a nivel fisiológico y funcional. El presente estudio se diseñó con la finalidad de estudiar la actividad realizada por un grupo de ancianos practicantes de Taichi (tai ji quan) para comprobar si son generalmente más activos. Y paralelamente estudiar su alimentación y observar sus posibles diferencias en cuanto a la actividad física y/o el sexo. Método: El trabajo se llevó a cabo con 41 personas (71 años) de las cuales 23 eran mujeres y dentro de ellas: n=11 activas y n=12 sedentarias. Y 18 hombres dentro de ellos: n=9 activos y n=9 sedentarios. Para evaluar su actividad física se realizó el cuestionario IPAQ. Para evaluar su alimentación se utilizó el programa Nutriber y como añadido a la alimentación se les pasó un cuestionario de adherencia a la dieta mediterránea. Resultados: A través del cuestionario IPAQ observamos que los sujetos que practican Taichi son más activos en las actividades de caminar, moderadas y vigorosas que los que no lo practican. En nuestro estudio se observa que para las ingestas de macronutrientes las proteínas se encuentran por encima de las recomendadas, mientras que en el caso de las grasas las ingestas son menores en ambos sexos y sin diferencias según la actividad física. En los micronutrientes las ingestas generalizadas para el Na, K, Ca, Mg, P y Cl son semejantes a las recomendadas, en cambio las ingestas de Zn de las mujeres están por debajo de las recomendadas. Todos los sujetos han presentado para las ingestas de vitaminas valores superiores al recomendado a excepción de la vitamina E con ingestas inferiores. El grupo de estudio presenta de forma general una alta adherencia a la dieta mediterránea siendo este grado de adherencia mayor en los sujetos activos. Conclusiones: Los sujetos que realizan Taichi son a su vez más activos que los que no lo realizan. Estos sujetos considerados activos son los que presentan mejores índices nutricionales así como una mayor adherencia a la dieta mediterránea

Efecto de la práctica del Taichi en las capacidades funcionales de personas mayores = Effect of Taichi practice in elderly funtional abilities

Objetivo: El envejecimiento involucra diversos cambios a nivel fisiológico, proceso que además se caracteriza por la pérdida de las capacidades físicas, con el consiguiente deterioro funcional de las personas mayores. El presente estudio se diseñó con la finalidad de establecer el efecto de una actividad física como el Taichi sobre la capacidad funcional de los ancianos medida a través de la Batería Senior Fitness Test. Método: El trabajo se llevó a cabo con 40 personas (71años) de las cuales 15 eran hombres y 25 mujeres. Ambos grupos además se subdividieron en sedentarios (n=19) y físicamente activos (n=21). Para evaluar la capacidad funcional de los sujetos se les realizó la batería de pruebas que componen el Senior Fitness Test (SFT). El grupo de personas que realizaban ejercicio practicaban Taichi una hora cuatro veces a la semana durante al menos 2 años. Resultados: En nuestro estudio se observa una mayor fuerza del tren superior e inferior en hombres en comparación con mujeres, mientras que la resistencia aeróbica, la agilidad y la flexibilidad es superior en las mujeres. Cuando se comparan sedentarios frente a personas que practican Taichi se observa una mejora en todas las cualidades físicas tanto en hombres como en mujeres. Conclusión: Un programa de Taichi mejora significativamente parámetros relacionados con la resistencia aeróbica, flexibilidad, agilidad y fuerza muscular, siendo cualidades que podrían ayudar a alejar a las personas mayores de la dependencia funcional, mejorando de esta manera su expectativa y calidad de vida

Exportación de conocimiento: Colombia como proveedor de seguridad para la lucha contra el terrorismo y el crimen internacional

El presente artículo pretende arrojar una serie de perspectivas relevantes en materia de seguridad contra el terrorismo y el crimen internacional desde la experiencia colombiana. Este trabajo articula dimensiones estratégicas de manera general, pero se enfoca en las relaciones con África, especialmente con el Cuerno de África. Este documento es una visión panorámica sobre una de las dimensiones en las que Colombia es exportador de conocimiento. En ese orden de ideas, se presentan líneas generales pero estratégicas en la materia, en especial en la lucha contra la piratería

El correo electrónico mediador de intercambios lingüísticos

El presente artículo tiene por objetivo dar a conocer algunos avances de una investigación que se realiza en el marco de una experiencia pedagógica cuya finalidad es el intercambio de mensajes electrónicos entre estudiantes de la Licenciatura en Lenguas Modernas de la Pontificia Universidad Javeriana que aprenden el francés y estudiantes franceses de la universidad de Franche-Comté en Francia que aprenden el español. La implementación de un dispositivo de este tipo es un medio adecuado para que los estudiantes practicando la lengua de aprendizaje (francés – español) mejoren su nivel de competencia comunicativa.This article aims at making known some advances of a research which is being carried out in the framework of a pedagogical experience whose aim is the interchange of e-mails between Colombian students of Modern Languages of Pontificia Universidad Javeriana and French students learning Spanish form Universidad Franche-Comté (France). The implementation of a device of this type is an adequate medium for student to improve his/her communicative level by practicing learning language (French – Spanish)