Bauschinger Effect in an Austenitic Steel: Neutron Diffraction and a Multiscale Approach
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ONE of the major issues in materials engineering is to satisfy requirements for the manufacturing of mechanical structures made of damage-resistant alloys. Engineering processes create defects at the surface and / or localized in the mechanical piece. These defects are characterized by cracks, micro-cracks and residual stresses which result in fast or slow damage of the mechanical parts during service. The choice of the alloy allows making the material more or less ductile to resist the various mechanical loadings. A better understanding of the mechanical properties of alloys and the prediction of those properties lead to optimization of manufacturing processes and cost reductions. Understanding the relationships between the microstructure and the mechanical properties is very important for this. Several experimental and theoretical works were done in recent decades to identify and describe realistically the main physical mechanisms observed in metallic materials. Many studies were performed on plasticity mechanisms, as dislocation microstructure, leading to the development of a crystal plasticity approach. Therefore, the homogenization approach was developed to predict the macroscopic behavior by linking the different physical mechanisms to the material behavior. JAMAL FAJOUI, Assistant Professor, DAVID GLOAGUEN, Professor, VINCENT LEGRAND, Assistant Professor, and GUY OUM, Doctor, are with the Universite´ de Nantes, Institut de Recherche en Ge´nie Civil et Me´canique (UMR CNRS 6183), 58, rue Michel Ange, BP 420, 44606 Saint-Nazaire Cedex, France. Contact e-mail: [email protected] JOE KELLEHER and WINFRIED KOCKELMANN, Doctors, are with the ISIS Facility, Science and Technology Facilities Council, Rutherford Appleton Laboratory, Harwell Oxford Didcot, Oxfordshire, OX11 0QX, England. Manuscript submitted July 8, 2015. Article published online February 22, 2016 2024—VOLUME 47A, MAY 2016
This kind of approach aims to deduce the macroscopic properties of materials from the characterization and analysis of their microstructure and their deformation mechanisms. This methodology is based on a combined transition level approach and experimental analysis.[1] Characterizations and mechanical validations (mechanical tests, diffraction analysis…) are performed at the local and macroscopic levels linked to the definition of the representative elementary volume (REV). Thus, it is necessary to define the suitable scale of basic volume (BV) or the element of REV. Therefore, the analysis of activated mechanisms allows the implementation of a multiscale method so as to determine the macroscopic behavior. Depending on the type of studied materials and the intended applications, the considered BV has to be different. For a polycrystalline aggregate, the grain represents the starting scale also called BV. According to its orientation, each grain has a different behavior related to the crystallographic nature of the strain mechanisms. In the monotonic loading cases, polycrystalline approaches such as self-consistent models
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