Optimization of phase transformation for the development of fatigue resistant materials

开发具有改进抗疲劳性能的材料及其表征方法是一个不断发展的研究领域，因为它可以在不影响安全性的情况下优化工程部件。提高金属抗疲劳性能的一种原始方法是优化裂纹扩展过程中相变的效益。文献调查表明，在某些特定条件下，相变可使疲劳强度提高50%。相变的主要好处是消耗机械能和产生闭合裂纹尖端的残余压应力。另一方面，循环载荷作用下的相变是复杂的，其效率受环境、微观结构、加载条件等参数的影响。更好地理解裂纹尖端相变的热力学和动力学及其对裂纹扩展机制的影响，将有助于开发具有更高抗疲劳性能的先进材料。这些都是我的发现基金项目的目标。

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.