Física conceptos básicos de la mecánica

Me alegra escribir esta primera lección con el rigor y la precisión de su documento cuyo compromiso es con la información y la formación al estudiante, y por ello debo estar atento y ser exigente en los temas aquí tratados. Esta y las demás lecciones recogen lo más importante en el área de la Física que los profesionales docentes casi nunca han puesto por escrito y al público; sus preparaciones de clase ordenadas, organizadas, y los resultados de sus trabajos, sus propuestas, sus consultas, sus reflexiones. Generalmente poco se considera que la experiencia propia, la experiencia personal es tan trascendental y tan válida como los resultados de una investigación. Este es un nuevo reto que, como sucede con las Lecciones de Matemáticas, dará fruto y excelente resultado, proporcionando los conocimientos y conceptos básicos de Física para fundamentar su estatus académico en la comunidad estudiantil. Así nos sentiremos satisfechos por dar sentido al trabajo realizado reconociendo hacia dónde caminar, en qué profundizar, cómo crear adaptaciones y darles perfil a las aplicaciones, intentando mejorar la relación enseñanza aprendizaje y dar así respuesta a necesidades del entorno. Agradezco a aquellos que deseen aportar sus sugerencias para que en un futuro tengamos un texto mejor para una excelente formación científica de nuestros estudiantes.

Otimização e análise mecânica de pastas geopoliméricas para uso em poços sujeitos à injeção cíclica de vapor

Oil wells subjected to cyclic steam injection present important challenges for the development of well cementing systems, mainly due to tensile stresses caused by thermal gradients during its useful life. Cement sheath failures in wells using conventional high compressive strength systems lead to the use of cement systems that are more flexible and/or ductile, with emphasis on Portland cement systems with latex addition. Recent research efforts have presented geopolymeric systems as alternatives. These cementing systems are based on alkaline activation of amorphous aluminosilicates such as metakaolin or fly ash and display advantageous properties such as high compressive strength, fast setting and thermal stability. Basic geopolymeric formulations can be found in the literature, which meet basic oil industry specifications such as rheology, compressive strength and thickening time. In this work, new geopolymeric formulations were developed, based on metakaolin, potassium silicate, potassium hydroxide, silica fume and mineral fiber, using the state of the art in chemical composition, mixture modeling and additivation to optimize the most relevant properties for oil well cementing. Starting from molar ratios considered ideal in the literature (SiO2/Al2O3 = 3.8 e K2O/Al2O3 = 1.0), a study of dry mixtures was performed,based on the compressive packing model, resulting in an optimal volume of 6% for the added solid material. This material (silica fume and mineral fiber) works both as an additional silica source (in the case of silica fume) and as mechanical reinforcement, especially in the case of mineral fiber, which incremented the tensile strength. The first triaxial mechanical study of this class of materials was performed. For comparison, a mechanical study of conventional latex-based cementing systems was also carried out. Regardless of differences in the failure mode (brittle for geopolymers, ductile for latex-based systems), the superior uniaxial compressive strength (37 MPa for the geopolymeric slurry P5 versus 18 MPa for the conventional slurry P2), similar triaxial behavior (friction angle 21° for P5 and P2) and lower stifness (in the elastic region 5.1 GPa for P5 versus 6.8 GPa for P2) of the geopolymeric systems allowed them to withstand a similar amount of mechanical energy (155 kJ/m3 for P5 versus 208 kJ/m3 for P2), noting that geopolymers work in the elastic regime, without the microcracking present in the case of latex-based systems. Therefore, the geopolymers studied on this work must be designed for application in the elastic region to avoid brittle failure. Finally, the tensile strength of geopolymers is originally poor (1.3 MPa for the geopolymeric slurry P3) due to its brittle structure. However, after additivation with mineral fiber, the tensile strength became equivalent to that of latex-based systems (2.3 MPa for P5 and 2.1 MPa for P2). The technical viability of conventional and proposed formulations was evaluated for the whole well life, including stresses due to cyclic steam injection. This analysis was performed using finite element-based simulation software. It was verified that conventional slurries are viable up to 204ºF (400ºC) and geopolymeric slurries are viable above 500ºF (260ºC)

Análise mecânica e microestrutural das ligas de cobalto-cromo de uso odontológico após sucessivas refundições

The cobalt-chromium alloy is extensively used in the Odontology for the confection of metallic scaffolding in partial removable denture. During the last few years, it has been reported an increasing number of premature imperfections, with a few months of prosthesis use. The manufacture of these components is made in prosthetic laboratories and normally involves recasting, using parts of casting alloy and parts of virgin alloy. Therefore, the objective of the present study was to analyze the mechanical properties of a commercial cobalt-chromium alloy of odontological use after successive recasting, searching information to guide the dental prosthesis laboratories in the correct manipulation of the cobalt-chromium alloy in the process of casting and the possible limits of recasting in the mechanical properties of this material. Seven sample groups were confectioned, each one containing five test bodies, divided in the following way: G1: casting only with virgin alloy; G2: casting with 50% of the alloy of the G1 + 50% of virgin alloy; G3: casting with 50% of the alloy of the G2 + 50% of virgin alloy; G4: casting with 50% of the alloy of the G3 + 50% of virgin alloy; G5: 50% of alloy of the G4 + 50% of virgin alloy; G6: 50% of alloy of the G5 + 50% of virgin alloy and finally the G7, only with recasting alloy. The modifications in the mechanical behavior of the alloy were evaluated. Moreover, it was carried the micro structural characterization of the material by optic and electronic scanning microscopy, and X ray diffraction.and fluorescence looking into the correlatation of the mechanical alterations with structural modifications of the material caused by successive recasting process. Generally the results showed alterations in the fracture energy of the alloy after successive recasting, resulting mainly of the increasing presence of pores and large voids, characteristic of the casting material. Thus, the interpretation of the results showed that the material did not reveal significant differences with respect to the tensile strength or elastic limit, as a function of successive recasting. The elastic modulus increased from the third recasting cycle on, indicating that the material can be recast only twice. The fracture energy of the material decreased, as the number of recasting cycles increased. With respect to the microhardness, the statistical analyses showedno significant differences. Electronic scanning microscopy revealed the presence of imperfections and defects, resulting of the recasting process. X ray diffraction and fluorescence did not show alterations in the composition of the alloy or the formation of crystalline phases between the analyzed groups. The optical micrographs showed an increasing number of voids and porosity as the material was recast. Therefore, the general conclusion of this study is that the successive recasting of of Co-Cr alloys affects the mechanical properties of the material, consequently leading to the failure of the prosthetic work. Based on the results, the best recommendadition is that the use of the material should be limited to two recasting cycles

Fabricación y caracterización físico-mecánica de biocomposites reforzados con fibras naturales. Aplicaciones en el sector náutico.

156 p.

Ing. Aurelio Salvador Fernández González : director de la EIAO que elevó mecánica a facultad

Aurelio Fernández G, fue alumno fundador de la Preparatoria Técnica “Álvaro Obregón” de la que llegó a ser su director luego de titularse en la Escuela Superior de Ingeniería Mecánica y Eléctrica y al tiempo de desarrollar su trayectoria profesional en el Departamento de Laminados de Fundidora Monterrey.

Análise de métodos para aplicação de ventilação natural em projetos de edificações em Natal-RN

Natural ventilation is an efficient bioclimatic strategy, one that provides thermal comfort, healthful and cooling to the edification. However, the disregard for quality environment, the uncertainties involved in the phenomenon and the popularization of artificial climate systems are held as an excuse for those who neglect the benefits of passive cooling. The unfamiliarity with the concept may be lessened if ventilation is observed in every step of the project, especially in the initial phase in which decisions bear a great impact in the construction process. The tools available in order to quantify the impact of projected decisions consist basically of the renovation rate calculations or computer simulations of fluids, commonly dubbed CFD, which stands for Computational Fluid Dynamics , both somewhat apart from the project s execution and unable to adapt for use in parametric studies. Thus, we chose to verify, through computer simulation, the representativeness of the results with a method of simplified air reconditioning rate calculation, as well as making it more compatible with the questions relevant to the first phases of the project s process. The case object consists of a model resulting from the recommendations of the Código de Obras de Natal/ RN, customized according to the NBR 15220. The study has shown the complexity in aggregating a CFD tool to the process and the need for a method capable of generating data at the compatible rate to the flow of ideas and are discarded during the project s development. At the end of our study, we discuss the necessary concessions for the realization of simulations, the applicability and the limitations of both the tools used and the method adopted, as well as the representativeness of the results obtained

Análise de componentes arquitetônicos para potencialização da ventilação natural com ênfase em captadores de vento

The building envelope is the principal mean of interaction between indoors and environment, with direct influence on thermal and energy performance of the building. By intervening in the envelope, with the proposal of specific architectural elements, it is possible to promote the use of passive strategies of conditioning, such as natural ventilation. The cross ventilation is recommended by the NBR 15220-3 as the bioclimatic main strategy for the hot and humid climate of Natal/RN, offering among other benefits, the thermal comfort of occupants. The analysis tools of natural ventilation, on the other hand, cover a variety of techniques, from the simplified calculation methods to computer fluid dynamics, whose limitations are discussed in several papers, but without detailing the problems encountered. In this sense, the present study aims to evaluate the potential of wind catchers, envelope elements used to increase natural ventilation in the building, through CFD simplified simulation. Moreover, it seeks to quantify the limitations encountered during the analysis. For this, the procedure adopted to evaluate the elements implementation and efficiency was the CFD simulation, abbreviation for Computer Fluid Dynamics, with the software DesignBuilder CFD. It was defined a base case, where wind catchers were added with various settings, to compare them with each other and appreciate the differences in flows and air speeds encountered. Initially there has been done sensitivity tests for familiarization with the software and observe simulation patterns, mapping the settings used and simulation time for each case simulated. The results show the limitations encountered during the simulation process, as well as an overview of the efficiency and potential of wind catchers, with the increase of ventilation with the use of catchers, differences in air flow patterns and significant increase in air speeds indoors, besides changes found due to different element geometries. It is considered that the software used can help designers during preliminary analysis in the early stages of design

Componentes actitudinales que impactan en el rendimiento académico de matemáticas en alumnos de cuarto semestre de la Facultad de Ingeniería Mecánica y Eléctrica de la UANL

Esta investigación tiene como propósito determinar cuáles son los componentes de las actitudes que impactan en un mayor rendimiento académico en las matemáticas, se trabajó con los alumnos de cuarto semestre de las carreras de Ingeniero en Aeronáutica (IAE) e Ingeniero en Materiales (IMT) de la Facultad de Ingeniería Mecánica y Eléctrica (FIME) de la UANL. El instrumento elegido para medir las actitudes de los alumnos fue un cuestionario de veinticinco ítems en formato tipo escala Likert, diseñado por Elena Auzmendi (1991) el cual está integrado por cinco dimensiones (utilidad, ansiedad, confianza, agrado y motivación). Para estimar el rendimiento académico de los alumnos en matemáticas se elaboró una prueba con preguntas o problemas con formato de opción múltiple en áreas de Cálculo Diferencial e Integral, Ecuaciones Diferenciales y Álgebra. Además de realizar un análisis de frecuencias, los componentes fueron analizados bajo un modelo de regresión lineal múltiple para el cual se verificaron cada uno de los supuestos básicos con que debe contar toda regresión utilizando el paquete estadístico STATA. Las variables que resultaron ser significativas en el presente estudio fueron las relacionadas al componente emocional o afectivo de las actitudes de los estudiantes, dichas variables son la ansiedad y el agrado, lo que nos hace reflexionar y buscar propuestas para atender estas dos dimensiones qué tanto impacto tienen en el rendimiento académico del estudiantado.

Propuesta de guía metodológica para la evaluación del costo-beneficio de la higiene y seguridad ocupacional dentro de las empresas mecánica automotríz ubicadas en el municipio de Soyapango. Caso ilustrativo.

Toda actividad laboral lleva implícito un riesgo inherente durante su desarrollo, y a medida aumenta este riesgo se genera mayor inseguridad, lo cual muchas veces no es percibido por los propietarios de las empresas causando una serie de problemas laborales. El problema se agudiza al descubrir que la pequeña empresa salvadoreña no cuenta con suficientes recursos para desarrollar estudios especializados que analicen la gravedad de las consecuencias que están afectando su interior, es por ello que la higiene y seguridad ocupacional deben ocupar un lugar importante dentro de la empresa. La finalidad del presente documento es aportar una herramienta práctica que ayude a identificar los riesgos que se presentan en el desarrollo de las labores que se realizan dentro de los talleres de mecánica automotriz, demostrar la gravedad de las consecuencias que pueden ocasionar en la salud de los empleados y la productividad de los mismos y al mismo tiempo permita cuantificar los beneficios derivados de la inversión en higiene y seguridad ocupacional. Mediante la investigación se determinó que la mayoría de los talleres se encuentran en condiciones físicas desfavorables para un mejor desempeño de las actividades de los trabajadores, para realizar la investigación de campo con el fin de determinar los problemas que tienen los talleres de mecánica automotriz se utilizaron fuentes primarias como; encuestas dirigidas tanto a los propietarios o encargados como a los empleados de los talleres del municipio de Soyapango, así como también se hizo uso de la observación directa; además fuentes secundarias como, libros de texto, trabajos de graduación, leyes, revistas e información de Internet. Entre algunas de las principales conclusiones que se determinaron a través de la investigación, se tuvieron: A pesar de la importancia que tiene el ambiente físico, para los propietarios este aspecto no es de gran relevancia. Como se puede apreciar gran parte de los talleres se encuentran en condiciones físicas desfavorables para un mejor desempeño. Entre las enfermedades que más afectan este sector se encuentran las relacionadas con las afecciones en las vías respiratorias, este cuadro se complica debido a las condiciones físicas existentes en los talleres y los factores derivados de las mismas. La gran mayoría de empleados cuenta con alguna medida de protección personal; sin embargo, estas no son siempre utilizadas, ya que el empleado utiliza de manera inadecuada su propio criterio para su uso, reflejo de ello son los accidentes que suceden con mayor frecuencia, entre los cuales están los golpes, cortadas y quemadas leves Con el fin de mejorar las actuales condiciones de higiene y seguridad dentro de los talleres: Se recomienda a los propietarios mejorar las condiciones físicas ambientales de los talleres. Se recomienda hacer conciencia a los empleados a cerca del uso constante del equipo de protección siempre que lo necesiten, por más sencillas que parezcan las actividades laborales a realizar; además se sugiere concentración y seriedad al momento de realizar actividades en las que puedan resultar con alguna lesión.

Estudo da influência da temperatura de brasagem nas uniões zircônia/aço inox 304 utilizando metalização mecânica

Metal-Ceramic (M/C) Zirconia-stainless steel interfaces have been processed through brazing techniques due to the excellent combination of properties such as high temperature stability, high corrosion resistance and good mechanical properties. However, some M/C interfaces show some defects, like porosity and cracks results in the degradation of the interfaces, leading even to its total rupture. Most of time, those defects are associated with an improper brazing parameters selection to the M/C system. In this work, ZrO2 Y-TZP and ZrO2 Mg - PSZ were joint with the stainless steel grade 304 by brazing using a eutectic silver-copper (Ag28Cu) interlayer alloy with different thermal cycles. Ceramic surfaces were previous mechanically metallized with titanium to improve adhesion of the system. The effect of temperature on the M/C interface was studied. SEM-EDS and 3 point flexural bend test were performed to evaluate morphology, chemical composition and mechanical resistance of the M/C interfaces. Lower thermal cycle temperatures produced better results of mechanical resistance, and more regular/ homogeneous reaction layers between braze alloy and metal-ceramic surfaces. Also was proved the AgCu braze alloy activation in situ by titanium

Diseño de una estrategia de mercadeo para la industria metal mecánica de El Salvador fabricante de herramientas manuales. Caso ilustrativo.

El presente trabajo de graduación incluye un estudio en la industria metal mecánica salvadoreña fabricante de herramientas manuales de metal, en especial a una empresa como caso ilustrativo, diseñándose una estrategia de mercadeo que le permita incrementar sus niveles de venta en un mercado competitivo. El desarrollo de la investigación se realizó en el área metropolitana de San Salvador por medio de entrevistas y encuestas dirigidas a las empresas fabricantes, distribuidores y consumidores finales; considerándose como consumidores los talleres de estructuras metálicas por ser los principales demandantes de los productos fabricados por la empresa en estudio; además se obtuvo información de otras fuentes, como: Banco Central de Reserva (BCR), Fundación Salvadoreña para el Desarrollo Económico y Social (FUSADES), Cámara de Comercio de El Salvador, Dirección General de Estadísticas y Censos (DIGESTYC). El análisis de la información recopilada permitió realizar un diagnóstico de la situación competitiva de mercado en que se encuentra la industria y la empresa en particular. Así mismo, se obtuvieron datos de importancia relativos al comportamiento del consumidor y la calificación que da a los productos de la metal mecánica fabricados en El Salvador. En cuanto a la empresa en estudio se determinó que tiene demanda principalmente en los talleres de estructuras metálicas; sin embargo, no existe una lealtad firme de marca; la rivalidad es intensa; los distribuidores ejercen un alto poder de negociación en cuanto a calidad; posee un número limitado de proveedores, lo que propicia un alto poder de negociación; además, existe limitada información acerca de las herramientas que fabrica. Al reconocer la situación de la empresa, se diseña la propuesta, especificándose la misión, visión, objetivos y estrategias para cada una de las variables del mercado, orientadas de manera que se incorporen a un plan de comercialización para cinco años; además, se incluyen presupuestos para dar a conocer el efecto financiero del diseño, el plan de implementación de la propuesta; así como, el control de dicho plan y las recomendaciones respectivas.

Plásticos reforçados a base de tecidos híbridos: efeitos da anisotropia e geometria normativa na caracterização mecânica e da fratura

As most current studies, reinforced plastics have been, in recent years, a viable alternative in building structural elements of medium and large, since the lightness accompanied by high performance possible. The design of hybrid polymer composites (combination of different types of reinforcements) may enable structural applications thereof, facing the most severe service conditions. Within this class of composite materials, reinforced the underlying tissues hybrid high performance are taking space when your application requires high load bearing and high rigidity. The objective of this research work is to study the challenges in designing these fabrics bring these materials as to its mechanical characterization and fracture mechanisms involved. Some parameters associated with the process and / or form of hybridization stand out as influential factors in the final performance of the material such as the presence of anisotropy, so the fabric weave, the process of making the same, normative geometry of the specimens, among others. This sense, four laminates were developed based hybrid reinforcement fabrics involving AS4 carbon fiber, kevlar and glass 49-E as the matrix epoxy vinyl ester resin (DERAKANE 411-350). All laminates were formed each with four layers of reinforcements. Depending on the hybrid fabric, all the influencing factors mentioned above have been studied for laminates. All laminates were manufactured industrially used being the lamination process manual (hand-lay-up). All mechanical characterization and study of the mechanism of fracture (fracture mechanics) was developed for laminates subjected to uniaxial tensile test, bending in three and uniaxial compression. The analysis of fracture mechanisms were held involving the macroscopic, optical microscopy and scanning electron microscopy

Avaliação de uma forrageira para a colheita mecânica do sorgo biomassa.

A oportunidade de utilização do sorgo biomassa como fonte para cogeração de energia nas usinas de cana-de-açúcar, durante o período de descanso desta cultura, permitiu à Embrapa Milho e Sorgo estabelecer um trabalho integrado com a indústria de máquinas para viabilizar a produção extensiva, principalmente na colheita mecânica, com a empresa Case New Holland, de Sorocaba-SP. Este trabalho foi muito importante para resolver um dos gargalos do sistema de produção do sorgo, que vinha utilizando as colhedoras de cana-de-açúcar, com modificações no arranjo das linhas de plantio, e com baixo rendimento. A possibilidade de utilização de uma forrageira, com alta capacidade operacional, entre 140 e 160 t/ha, com o arranjo de plantas normal, sem modificações, indicava ser um grande potencial para testes com o híbrido BRS 716, que vem demonstrando excelentes produtividades de massa verde, entre 120 e 150 t/ha, em um curto período de 150 a 180 dias. Este trabalho apresenta resultados inéditos no mundo, por sermos pioneiros com a cultura do sorgo biomassa, e teve a participação da Usina Santa Vitória, em Santa Vitória-MG, da empresa Energias Renováveis do Brasil - ERB; e da Usina Rio Vermelho, em Dracena-SP, que plantaram grandes áreas para testes dos sistemas de produção, além da Embrapa Meio Ambiente, em Jaguariúna, SP, com uma área de testes, de 5 ha.