Optimization of phase transformation for the development of fatigue resistant materials

具有更好的抗疲劳性能的材料及其表征方法的开发是一个日益增长的研究领域，因为它允许在不损害安全性的情况下对工程部件进行优化。提高金属疲劳抗力的一个原始方法是优化裂纹扩展过程中相变的益处。文献综述表明，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并产生闭合裂纹尖端的压缩残余应力。另一方面，循环载荷作用下的相变是复杂的，其效率受环境、显微组织、加载条件等多个参数的影响。更好地理解1)裂纹尖端相变的热力学和动力学，以及2)它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。这些都是我的发现资助计划的目标。 在头五年结束时，我开发的知识和实验结果将很容易扩展到工程应用中，例如疲劳关键应用(例如水轮机转轮和起落架)的钢的优化以及避免灾难性故障的机械和环境条件的控制。这对我目前正在与之合作的许多本地和全球行业(例如魁北克水电、阿尔斯通、Velan和Héroux Devtek)具有重要意义。我的研究项目的社会作用是为减少燃料消耗和温室气体排放做出贡献，因为开发的材料将用于设计更轻的产品。 提出的研究方案是独一无二的，因为它寻求对各种环境中循环载荷下裂纹尖端的相变进行深入的了解和控制。在这个主题上发表的工作非常有限，因为这种相变通常用于改善材料在单调应力下的延性和韧性。我的研究计划的特殊性取决于我对量化和理解疲劳损伤机制及其与材料微观结构的关系的兴趣。在机械和材料工程领域，这种应对多学科挑战的详细研究还没有进行过。 我的团队拥有执行拟议工作所需的技能和知识，因为我们自2006年以来一直致力于金属材料的疲劳行为，自2001年以来一直致力于失效分析。我们开发了各种先进的实验和分析策略来测量、观察和了解金属，更具体地说是钢和铝合金的疲劳失效机制。在魁北克省，我被我的同行和行业合作伙伴认为是在这个主题上实验最多的研究人员之一。 最后，我提出的研究计划将有助于培训4名高素质的工程师和5名实习生，他们将获得物理冶金、失效分析和断裂力学方面的技能和知识。这类背景在魁北克很受欢迎，特别是航空航天、运输和能源行业。不幸的是，在过去的五年里，魁北克发现了这种类型的培训，特别是在2008年蒙特利尔理工学院材料科学本科课程关闭的情况下。在本科阶段失去这种专业形成的影响，给我对知识的贡献和我的培训计划的原创性带来了额外的价值。

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.