Quantification of 3-D Effects of Microstructure on Fatigue Crack Initiation and Early Growth in Planar Slip Alloys

技术总结：本研究项目的PI建议开发一种基于微观结构的模型，以量化平面滑移合金（如AA 2026、2524和2099 Al合金）中的疲劳裂纹萌生和早期生长，首先，通过确定短疲劳裂纹抗性与裂纹平面偏转的扭转分量之间的定量关系，跨越颗粒-基体界面或晶界，其次，通过计算从颗粒开始的微裂纹的生长速率，并考虑这些合金中三维的驱动力和阻力。聚焦离子束将被用来制造一个微缺口具有一个受控的扭转角与主滑移面在粗晶粒的合金，并使一系列的横截面的断裂颗粒在疲劳后的样品表面。将从作为扭转角的函数的测得的裂纹扩展速率数据中提取对来自缺口的微裂纹扩展的阻力。在PI的晶体学模型中引入阻力和驱动力将使得能够在三维中量化来自合金表面中的颗粒的微裂纹的生长行为。使用该模型将允许识别合金中最佳高周疲劳性能所需的微观结构和织构。该模型也将有助于阐明微观裂纹扩展行为之间的差异在合金表面上观察到的机制。非技术摘要：该项目预计将导致改善铝合金的疲劳性能，这可能会对航空航天和汽车工业产生重大影响。在这方面，拟议的研究有可能产生更广泛的社会影响。 合金工业作为一个整体也将受益于所开发的方法，因为确定理想的微观结构和纹理，导致高性能合金的最佳抗疲劳性将推进合金设计。此外，该研究项目将有助于为铝，汽车和航空航天行业培养训练有素的年轻技术毕业生。PI将通过开发两个与项目研究结果相关的项目，将研究工作融入他的教学活动中，用于他的材料科学和工程课程。本科生也将参与创建三维动画模型的裂纹增长跨越晶界，三维微观结构和X射线衍射。这些模型将与最新研究结果一起在网站上公布，供公众查阅。PI还将在矿物，金属材料学会年会上组织一系列关于金属材料疲劳损伤的研讨会，以便在研究界成员和合金行业的工程师中有效传播研究成果。

TECHNICAL SUMMARY:The PI of this research project proposes to develop a microstructure-based model to quantify fatigue crack initiation and early growth in a planar slip alloy, such as AA2026, 2524, and 2099 Al alloys, first, by identifying the quantitative relationship between short fatigue crack resistance and the twist component of crack plane deflection across either the particle-matrix interface or grain boundaries and, second, by calculating the growth rate of a micro-crack initiating from a particle and taking into account both the driving force and resistance in three dimensions in these alloys. A focused ion beam will be employed to fabricate a micro-notch having a controlled twist angle with the primary slip plane in a coarse grain of the alloy and to make serial cross-sections of fractured particles found in the sample surface after fatigue. The resistance to micro-crack growth from the notch will be extracted from measured crack growth rate data as a function of the twist angle. Incorporation of both the resistance and driving force in the PI's crystallographic model will enable quantification in three dimensions of the growth behavior of the micro-crack from a particle in the surface of the alloys. Using this model will allow identification of the desirable microstructure and texture for optimum high-cycle fatigue properties in the alloys. The model will also help to elucidate the mechanism for the observed differences in micro-crack growth behavior among different particles on a surface in the alloys.NON-TECHNICAL SUMMARY:This project is expected to result in improved fatigue properties in aluminum alloys, which may have significant impact on the aerospace and automotive industries. In this regard, the proposed research has potential for wider societal impacts. The alloy industry as a whole will also benefit from the methodology to be developed, as identification of the desirable microstructure and texture that lead to optimum fatigue resistance in high-performance alloys will advance alloy design. Further, this research project will help to develop well-trained young technical graduates for the aluminum, automotive, and aerospace industries. The PI will integrate the research work into his teaching activities by developing two projects, related to project findings, for use in his materials science and engineering courses. Undergraduate students will also participate by creating three-dimensional animation models of crack growth across grain boundaries, three-dimensional microstructure, and X-ray diffraction. These models will be made available on a website, together with the latest research results, for access by the public. The PI will also organize a symposium series on fatigue damage in metallic materials at The Mineral, Metals & Materials Society annual meetings to disseminate effectively research findings among members of the research community and engineers from the alloy industry.