Análisis multiescala de tensiones residuales en una aleación de aluminio monofásica policristalina

Abstract

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.