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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Modeling of the elastic mechanical behavior of thin compliant joints under load for highest-precision applications

Torres Melgarejo, Mario André 16 October 2018 (has links)
For the most demanding measurement tasks in force metrology flexure hinges in compliant mechanisms represent a key component. To enhance the mechanical properties of devices like weighing cells, the ability of precise modeling of flexure hinges is essential. The present scientific work focuses on the modeling of the mechanical behavior of a single flexure hinge subjected to geometric deviations and non-ideal loading conditions as those encountered in weighing cells. The considered hinge has a semi-circular contour and a large width compared to its minimum notch height. This geometry is modeled using the finite element method. Requirements for a trustworthy and efficient computation are elaborated under the consideration of geometric deviations for later parametric studies. Analytical expressions found in the literature are compared to numerical results to prove the validity of their assumptions for thin hinges. The model is used for studying the deviation of the stiffness in non-ideal flexure hinges. Sources of deviation are identified and described by parameters. The range of values for each parameter is chosen on the basis of available manufacturing technology. Influential parameters are identified through a sensitivity analysis. The effect of loading conditions is studied in the context of the application in weighing cells. For the enhancement of the overall sensitivity, the stiffness of the flexure hinges can be reduced. One option, the alteration of the geometry by adding a flexure strip in the center of the semi-circular flexure hinge is studied in comparison to existing analytical equations. The effects of ground tilts for a single loaded flexure hinge are investigated as a foundation for future modeling of a tilt insensitive state of a weighing cell mechanism (autostatic state). By adjusting the vertical position of the center of mass of the lever, the tilt sensitivity can be reduced to zero. An approach to find the position for this state is presented considering the numerical limitations of finite element modeling. Using this approach, the variation of the sought position is evaluated for different values of the design parameters. / Tesis
2

Modeling of the elastic mechanical behavior of thin compliant joints under load for highest-precision applications

Torres Melgarejo, Mario André 16 October 2018 (has links)
For the most demanding measurement tasks in force metrology flexure hinges in compliant mechanisms represent a key component. To enhance the mechanical properties of devices like weighing cells, the ability of precise modeling of flexure hinges is essential. The present scientific work focuses on the modeling of the mechanical behavior of a single flexure hinge subjected to geometric deviations and non-ideal loading conditions as those encountered in weighing cells. The considered hinge has a semi-circular contour and a large width compared to its minimum notch height. This geometry is modeled using the finite element method. Requirements for a trustworthy and efficient computation are elaborated under the consideration of geometric deviations for later parametric studies. Analytical expressions found in the literature are compared to numerical results to prove the validity of their assumptions for thin hinges. The model is used for studying the deviation of the stiffness in non-ideal flexure hinges. Sources of deviation are identified and described by parameters. The range of values for each parameter is chosen on the basis of available manufacturing technology. Influential parameters are identified through a sensitivity analysis. The effect of loading conditions is studied in the context of the application in weighing cells. For the enhancement of the overall sensitivity, the stiffness of the flexure hinges can be reduced. One option, the alteration of the geometry by adding a flexure strip in the center of the semi-circular flexure hinge is studied in comparison to existing analytical equations. The effects of ground tilts for a single loaded flexure hinge are investigated as a foundation for future modeling of a tilt insensitive state of a weighing cell mechanism (autostatic state). By adjusting the vertical position of the center of mass of the lever, the tilt sensitivity can be reduced to zero. An approach to find the position for this state is presented considering the numerical limitations of finite element modeling. Using this approach, the variation of the sought position is evaluated for different values of the design parameters. / Tesis
3

Evaluación del espaciamiento sobre el cordón en las uniones tubulares tipo “K” compuesto de perfiles cuadrados en el cordón y diagonales

Atachahua Pio, James Felix 31 August 2023 (has links)
En los últimos años, el uso de estructuras metálicas con perfiles tubulares ha experimentado un notable aumento debido a su comportamiento estructural y su aspecto estético en las construcciones. Como resultado, se han desarrollado normativas para regular el dimensionamiento y comportamiento de las uniones de este tipo de perfiles estructurales. Los programas de análisis por elementos finitos se han convertido en herramientas poderosas para simular y optimizar el comportamiento de las estructuras. En este trabajo, se presenta un estudio numérico de uniones soldadas tipo K con espaciamiento, utilizando perfiles tubulares de acero de sección cuadrada en las diagonales y el cordón. Se desarrollaron modelos numéricos con un estudio de refinamiento de malla y condiciones de borde para determinar la configuración más eficiente. Los modelos se calibraron utilizando ensayos experimentales de autores citados en la bibliografía, y se llevó a cabo un estudio paramétrico variando el espaciamiento entre las diagonales y el material de los perfiles disponibles en el mercado nacional. Se compararon las tensiones máximas antes de la falla según los criterios establecidos por la normativa. En general, los modelos calibrados mostraron una excelente correlación con los ensayos experimentales, validando el estudio paramétrico de las uniones que permiten identificar configuraciones seguras de uniones tubulares, optimizando el proceso de diseño y evitando costosos ensayos experimentales. Los resultados obtenidos demostraron que las uniones con menor espaciamiento son más resistentes.

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