Publication: Análisis multiescala de tensiones residuales en una aleación de aluminio monofásica policristalina
Loading...
Files
Official URL
Full text at PDC
Publication Date
2015-02-09
Authors
Advisors (or tutors)
Editors
Journal Title
Journal ISSN
Volume Title
Publisher
Universidad Complutense de Madrid
Citations
Exportar
Abstract
Las exigencias actuales a las que se someten a los materiales de altas prestaciones, utilizados especialmente en la industria aeroespacial, aeronáutica y del transporte, requieren un conocimiento exhaustivo de sus propiedades mecánicas. En particular, el conocimiento del estado de tensiones residuales es fundamental para mejorar el comportamiento mecánico del material y su tiempo de vida en servicio en las aplicaciones estructurales para las cuales están diseñados. Las Tensiones Residuales, TR, se generan tanto en la superficie como en el interior del material por el hecho de someterlo a procesos termomecánicos no homogéneos. Son tensiones que están presentes en el material aún en ausencia de una carga externa aplicada. Se dividen en distintas categorías dependiendo de la escala en la que varían. Así, se tienen TR macroscópicas (tipo I), que varían en la escala de las dimensiones de la muestra, y TR microscópicas, que varían en la escala del tamaño de grano (tipo II) o inferior (tipo III). Ambas están íntimamente relacionadas con la microestructura del material y el proceso termomecánico al que se ha sometido, pero su determinación y el efecto en el comportamiento mecánico de los metales es muy diferente. Habitualmente, cuando en el diseño estructural se tienen en cuenta estas tensiones, sólo se atiende a la influencia de las TR macroscópicas ya que hasta la fecha no existen estudios que cuantifiquen la magnitud de las tensiones microscópicas. En este trabajo se pretende aportar un paso en el ámbito de las TR microscópicas tipo II sobre la base de los datos que se obtienen por difracción de radiación de sincrotrón. Para ello se ha establecido un protocolo de separación de tensiones, que permite cuantificar las tensiones. Para el estudio se ha utilizado una aleación monofásica de aluminio y se ha recurrido a modelos existentes y conceptos que ya se emplean en materiales polifásicos o compuestos (con dos o más fases bien diferenciadas que poseen distintas propiedades físico-químicas). Otro de los retos que aborda esta investigación es determinar, mediante el desarrollo de un modelo elastoplástico, una ecuación que permita describir el estado de TR intergranulares, TRI, que son aquellas que se manifiestan entre granos vecinos como consecuencia de soportar esfuerzos o tensiones diferentes. Los principales objetivos de este trabajo son llevar a cabo un análisis multiescala de las TR y correlacionarlo con la microestructura del material. Por otro lado, también se ha estudiado el proceso de relajación de dichas TR con el fin de obtener parámetros cinéticos a través de la correlación entre los fenómenos de relajación de tensiones residuales y los fenómenos de fluencia convencionales. El estudio de TR se ha realizado a partir de medidas de la distancia interplanar obtenidas mediante difracción de radiación sincrotrón en una aleación de aluminio monofásica policristalina.
The present requirements of high-performance materials, in particular in the aeronautical, aerospace and transport sectors, obliges to a deep knowledge of their mechanical properties. In particular, knowledge of the residual stress state of materials is crucial if the improvement of the mechanical performance of materials and service life of components for structural applications is sought. The residual stress, RS, is generated in both the surface as well as in the interior of materials as a result of non-homogeneous thermo-mechanical processes. These are stresses present in the absence of externally applied forces. The can be divided in different categories, depending upon the length scale. The macroscopic residual stress (type I), varies in a scale similar to the sample dimension, whereas the microscopic one varies in the scales of the grain size (type II) or even at a lower scale (type III). Both are intimately related with the microstructure and the thermo-mechanical process underwent by the material. However, the way to determine these stresses and their effect on the mechanical behavior is quite different. Typically, only the macroscopic residual stress state is taken into consideration during the design of structural components. This is because the exact magnitude of the microscopic one is not yet known. The present study is aimed at investigating the type II microscopic residual stress taking advantage of x-ray diffraction data supplied by a synchrotron source. For this purpose, a protocol that separates the macroscopic and the microscopic residual stress is proposed. In this way the magnitude of the macroscopic and microscopic residual stress can be calculated. For this study, current models and concepts presently used in the study of residual stresses in composite materials are used and applied to a monolithic commercial aluminum alloy, 2014. Further challenge of the present investigation refers to the study of inter-granular stresses, or the stresses generated between neighbor grains undergoing different stresses. In summary, the main objective of the present investigation is the multi-scale analysis of the RS state and its correlation with the materials microstructure. In addition, also the study of the stress relaxation process, in connection with conventional creep kinetics parameters, has been carried out. The RS study has been conducted on the basis of lattice spacing measurements obtained by synchrotron x-ray diffraction in a commercial aluminum alloy, as above stated.
The present requirements of high-performance materials, in particular in the aeronautical, aerospace and transport sectors, obliges to a deep knowledge of their mechanical properties. In particular, knowledge of the residual stress state of materials is crucial if the improvement of the mechanical performance of materials and service life of components for structural applications is sought. The residual stress, RS, is generated in both the surface as well as in the interior of materials as a result of non-homogeneous thermo-mechanical processes. These are stresses present in the absence of externally applied forces. The can be divided in different categories, depending upon the length scale. The macroscopic residual stress (type I), varies in a scale similar to the sample dimension, whereas the microscopic one varies in the scales of the grain size (type II) or even at a lower scale (type III). Both are intimately related with the microstructure and the thermo-mechanical process underwent by the material. However, the way to determine these stresses and their effect on the mechanical behavior is quite different. Typically, only the macroscopic residual stress state is taken into consideration during the design of structural components. This is because the exact magnitude of the microscopic one is not yet known. The present study is aimed at investigating the type II microscopic residual stress taking advantage of x-ray diffraction data supplied by a synchrotron source. For this purpose, a protocol that separates the macroscopic and the microscopic residual stress is proposed. In this way the magnitude of the macroscopic and microscopic residual stress can be calculated. For this study, current models and concepts presently used in the study of residual stresses in composite materials are used and applied to a monolithic commercial aluminum alloy, 2014. Further challenge of the present investigation refers to the study of inter-granular stresses, or the stresses generated between neighbor grains undergoing different stresses. In summary, the main objective of the present investigation is the multi-scale analysis of the RS state and its correlation with the materials microstructure. In addition, also the study of the stress relaxation process, in connection with conventional creep kinetics parameters, has been carried out. The RS study has been conducted on the basis of lattice spacing measurements obtained by synchrotron x-ray diffraction in a commercial aluminum alloy, as above stated.
Description
Tesis inédita de la Universidad Complutense de Madrid, Facultad de Ciencias Físicas, Departamento de Física de Materiales, leída el 16-12-2015