Optimization of phase transformation for the development of fatigue resistant materials

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The development of materials with improved fatigue resistance and their characterization methods is a growing field of research as it allows the optimization of engineering components without compromising safety. One original way to improve the fatigue resistance of metals is to optimize the benefits of phase transformation during the propagation of cracks. The survey of literature reveals that phase transformation can increase fatigue strength by 50% in some specific conditions. The main benefits of phase transformation are to consume mechanical energy and to produce compressive residual stresses closing the crack tip. On the other hand, phase transformation under cyclic loads is complex and its efficiency is influenced by several parameters such as the environment, the microstructure, the loading conditions. A better understanding of 1) the thermodynamic and kinetic of phase transformation at crack tip, and 2) its effect on the crack propagation mechanisms, could lead to the development of advanced materials with improved fatigue resistance. These are the objectives of my discovery grant program.* *At completion of the first five years, the knowledge and experimental results I will have developed will easily be extended to engineering applications such as the optimization of steels for fatigue critical applications (e.g. hydraulic turbine runners and landing gears) and the control of mechanical and environmental conditions to avoid catastrophic failures. This is of significant importance for many local and global industries with whom I am currently collaborating (e.g. Hydro-Quebec, Alstom, Velan and Héroux Devtek). The societal role of my research program is to contribute to the reduction of fuel consumption and green house emissions as the developed materials will be used to design lighter products. **The proposed research program is unique as it seeks a deep understanding and control of phase transformation at crack tip, under cyclic loads in a variety of environments. Very limited work on this topic has been published as such phase transformations are conventionally used to improve the ductility and toughness of materials under monotonic stresses. The specificity of my research programs relies on the interest I have toward the quantification and understanding of fatigue damage mechanisms and their relation to the material microstructure. Such a detail research tackling multidisciplinary challenges, in mechanical and material engineering, has not been performed yet.**My team has the skills and knowledge necessary to perform the proposed work as we have been working on the fatigue behavior of metallic materials since 2006 and on failure analysis since 2001. We have developed a variety of advanced experimental and analytical strategies to measure, observe and understand fatigue failure mechanisms in metals and more specifically in steels and aluminum alloys. In the province of Quebec, I am considered by my peers and by industrial partners one of the most experimented researcher on the topic. **Finally, the research program I propose will contribute to the training of 4 highly qualified engineers and 5 interns that will acquire skills and knowledge in physical metallurgy, failure analysis and fracture mechanic. This type of background is prized in Quebec, especially by the aerospace, transport and energy industries. This type of training has unfortunately been uncovered in Quebec during the last five years especially with the closure, in 2008, of the material science undergraduate program of Ecole Polytechnique de Montreal. The impact of loosing this specialized formation at the undergraduate level is giving a plus value to my contribution to knowledge and to the originality of my training program.