Buscamos un candidato para una tesis en mecánica de los materiales en nuestro laboratorio, el Grupo de Física de los Materiales (http://gpm.labos.univ-rouen.fr/) en Rouen, Francia, con inicio en octubre del 2013. Se trata de un estudio del comportamiento mecánico en fatiga de materiales metálicos en relación con la micro-estructura. El trabajo sera experimental y consistirá en realizar ensayos mecánicos y observación micro-estrucurales mediante la microscopia electrónica de transmisión (la descripción completa de la tesis esta al final). La tesis esta financiada con una beca de la región Haute-Normandie con un salario bruto de unos 1600 € mensuales.
El candidato deberá tener buenos conocimientos en propriedades mecánicas, metalurgia y ciencia de materiales así como un buen nivel de Ingles para las comunicaciones científicas. Las personas interesadas deberán enviar un curriculum y las notas obtenidas en el diploma universitario a los contactos siguientes:
Clément Keller (firstname.lastname@example.org) y Lakhdar Taleb (email@example.com)
descripción de la tesis:
Title : Understanding of the origin of the thermo-mechanical memory effect on the cyclic mechanical behavior of metallic materials with different stacking fault energies.
Metallic components in aerospace, automotive or energy production applications are generally submitted to cyclic mechanical loadings. The investigation of the mechanical behavior during cyclic loadings of metallic materials has been hence the subject of many studies in the past to understand the deformation mechanisms and correctly predict the lifetime of metallic components. However, many aspects of the cyclical behavior are still unclear, in particular the memory effect of the mechanical behavior. When a metallic sample is subjected to a first thermo-mechanical loading (strain amplitude and temperature), the mechanical behavior during a second loading of lower amplitude will depend, under given conditions, on the characteristics of the first loading. This memory effect of the first high-amplitude loading seems to depend on the stacking fault energy of the material, on the strain amplitude (for cyclic or monotone loading), on the temperature and on the loading path. The existence of this memory effect generally reduces the lifetime of the materials and the understanding of its mechanisms is essential for a correct prediction of the mechanical behavior of metallic parts for industrial purpose.
The objective of this thesis is to continue the work initiated in our team on this subject and thus to contribute to the understanding of the memory effect on the mechanical behavior of metallic alloys subjected to cyclic loadings. Through the use of three f.c.c.materials with different stacking fault energies (Cu, austenitic stainless steel 316L and Ni20Cr) ensuring different deformation mechanisms, the purpose is to analyze the mechanisms of the memory effect during the transition between several mechanical loadings of different amplitudes.
To this aim, two experimental studies will be performed. The first one is linked to the investigation of the evolution of the back-stress and effective stress during cyclic loading for different pre-hardening conditions (tensile or cyclic) in order to identify, for each material, the stress component responsible for the memory effect. The second one, based on the use of transmission electron microscopy, is focused on the evolution of the dislocation structures during the transition between two mechanical loadings of different strain amplitudes. The goal of this second part is to characterize the structures of dislocations responsible for the memory effect. Both experimental studies are complementary and should help us to correctly understand the origin of the memory effect and to draw influence maps based on the stacking fault energy and pre-loadings.
This subject is a continuation of the work developed in the research team in mechanics of materials (ERMECA) of the Material Physics Group (CNRS - University - INSA Rouen) on the experimental and numerical analysis of the cyclic mechanical behavior of alloys. The investigations of the team are based on an advanced mechanical testing system for the analysis of the mechanical behavior and on the electron microscopy platform of the laboratory (SEM EBSD and TEM) for the microstructural analysis.
The candidate will be responsible for the mechanical behavior analysis and for the microstructural observations (TEM / SEM). The candidate should have a taste for experimental work and skills in mechanics and material science. A good English level is required for written and oral communications.