Atomistic and Microstructural Computational Fatigue Design and Integrated Creep-Fatigue Theory for High-Temperature Alloys

在汽车、飞机、压缩机、泵、涡轮机等承受循环载荷的部件的所有使用故障中，疲劳至少占90%。传统上，工程师和研究人员必须进行测试以确定材料的疲劳性能，这会导致高昂的时间和金钱成本，从而延长机械/结构系统的材料和部件设计的开发周期。最近的研究表明，材料的低周疲劳寿命可以用材料的物理性质来表示，包括Burgers矢量、剪切模量和表面能。高周疲劳本质上是一个微观组织低周疲劳裂纹形核和扩展的过程。在这些认识的启发下，本研究提出了一种计算疲劳设计方法，旨在寻找具有优异抗疲劳性能的新型高温合金。建立了基于微观结构和第一性原理密度泛函理论(DFT)相结合的多晶金属裂纹形核寿命的数值模型，并用该模型预测了从低周疲劳寿命到高强疲劳寿命这一较宽载荷范围内多晶金属的裂纹形核寿命。此外，利用晶内和晶界位错滑动和攀移的变形机制，本文还将提出高温合金的整体理论框架--蠕变-疲劳综合理论(ICFT)。基于第一个基石建立的理论模型包含了所有可能的变形机制，而基于第二个基石的理论模型描述了导致断裂的损伤累积过程，从而定义了疲劳、蠕变和热机械疲劳组合的一般加载条件下的寿命。利用这一理论，一种新材料的开发只需要有限的实验室测试，这样材料在复杂加载条件下的行为就可以与基本的变形机制联系起来。提出的理论和模型一旦建立，将加快材料的开发和应用，以满足21世纪和未来快速增长的技术需求和严格的环境要求。它们还对现有或新设计的机械系统的预后和健康管理具有重要意义，具有准确的寿命预测，在生命周期管理方面节省了大量资金。除了对研究领域的好处外，拟议的研究还规划了高素质人员的培训(HQP)，并认真考虑了公平、多样性和包容性(EDI)。利用这项研究成果设计新材料和维护机械系统以满足燃气轮机行业不断增长的需求所节省的时间和成本肯定会使加拿大的经济和社会受益并做出贡献。

Fatigue accounts for at least 90 percent of all service failures of components subjected to cyclic loading, as experienced by automobiles, aircraft, compressors, pumps, turbines, etc. Traditionally, engineers and researchers have to perform testing to determine a material's fatigue property, which results in high costs in time and money, thus prolonging the development cycle in material and component design for mechanical/structural systems. Recent research has reported that the low cycle fatigue (LCF) life of a material can be formulated in terms of material's physical properties including Burgers vector, shear modulus and surface energy. High cycle fatigue (HCF) is, in essence, a process of microstructural LCF crack nucleation plus crack propagation. Enlightened by these understandings, a computational fatigue design approach is proposed in the present research, aiming to search for new high-temperature alloys with superior fatigue resistance. A microstructure-based numerical model combined with first-principles density functional theory (DFT) will be developed and then used to predict the crack nucleation life of polycrystalline metals for a wide spectrum of loading from LCF to HCF. Furthermore, utilizing the deformation mechanisms involving glide and climb of dislocations within grain interior and along grain boundaries, a holistic theoretical framework - the integrated creep-fatigue theory (ICFT) for high-temperature alloys will also be proposed in the present research. The theoretical model established based on the first cornerstone leads to constitutive laws encompassing all possible deformation mechanisms and that based on the second cornerstone describes the damage accumulation process leading to fracture, and thus defines the life under general loading conditions that involve a combination of fatigue, creep and thermomechanical fatigue. Using this theory, only limited laboratory-testing will be required for a new material development such that material behavior under complicated loading conditions can be linked to the fundamental deformation mechanisms. Once established, the proposed theory and model will speed up material development and application to meet the fast-growing technological demands and stringent environmental requirements in the 21st century and future. They also have a great implication in prognosis and health management of existing or newly designed mechanical systems, with accurate life prediction, offering tremendous savings in life cycle management. In addition to the benefits for the research field, the proposed research has also planned the training of Highly Qualified Personnel (HQP) with serious consideration of Equity, Diversity and Inclusion (EDI). The time and cost saving using this research outcomes to design new materials and maintain mechanical systems to meet continuously increasing requirements for the gas turbine industry will certainly benefit and contribute to the economy and society of Canada.