CAREER: Quantitative Understanding of the Effects of Micro- and Macro-texture on Fatigue Crack Initiation and Early Growth in high Performance Alloys

技术：这个职业项目解决了晶界对短疲劳裂纹扩展的阻力，以及晶体组织和晶粒结构对高性能合金疲劳性能的影响。目前已有的模型在计算短疲劳裂纹扩展时，都没有考虑到微观组织的三维效应，因此其成功程度有限。这项研究是建立在PI最近成功地确定晶界裂纹平面挠度的扭转和倾斜分量作为控制跨界短裂纹扩展行为的关键因素的基础上的。为了揭示裂纹面挠度与裂纹扩展阻力之间的定量关系，本研究将对带有细缺口的单晶合金进行独特设计的疲劳实验。在具有不同织构的新一代高强度铝合金中，利用电子背散射衍射技术详细研究织构对疲劳性能的影响。通过考虑晶界与裂纹之间的三维相互作用以及合金织构的影响，从所有这些实验中获得的数据将用于建立一个三维模型来量化短疲劳裂纹的扩展行为。预计该项目的结果将1)量化晶界对短疲劳裂纹扩展的阻力，2)确定最佳织构，从而获得更平衡的力学性能，特别是疲劳性能，以及3)开发3D模型以更好地模拟短裂纹扩展，从而改进关键工程部件的寿命预测方法。非技术：定量理解短疲劳裂纹与晶界的相互作用对于设计更安全的工程结构（如飞机和航天器）以及更可持续地使用材料至关重要。在这个项目中，研究工作将融入PI的教学活动中，研究结果也将用于推动材料教育。我们将开设一门新的晶体织构课程，目的是为了弥补织构领域广泛的研究与不足的教育之间的差距。目前，在美国很少有大学开设这样的课程。除了研究生，本科生也将通过参与这个项目的实验和理论活动来进行纹理理论和研究方面的训练。作为该项目的外展活动，PI还将开发一个关于纹理的在线自学课程，以促进PI大学以外的纹理教育，并帮助培训材料工业的技术人员关于纹理和金属材料加工过程中控制纹理的重要性。我们将积极寻求有关这些课程的反馈，并将其用于进一步提高这些课程的有效性。

TECHNICAL: This CAREER project addresses the resistance of grain boundaries to short fatigue crack growth and the effects of crystallographic texture and grain structure on the fatigue properties in high performance alloys. Currently, none of the existing models are able to take into account the 3-dimensional effects of microstructure in calculating short fatigue crack growth, and, therefore, their success is limited. This research is built on the PI's recent success in identifying the twist and tilt components of crack plane deflection at grain boundaries as the key factors that control the growth behavior of short cracks across the boundaries. In this research, a uniquely designed fatigue experiment on a single crystal alloy with a fine notch will be carried out in order to reveal the quantitative relation between crack plane deflection and the resistance to crack growth. The effects of texture on the fatigue properties will also be studied in details with electron backscatter diffraction in new generation high strength aluminum alloys that have different textures. The data obtained from all these experiments will be used to develop a 3-d model to quantify the growth behavior of short fatigue cracks by taking into account 3-d interaction between grain boundaries and the crack, and the effects of texture in the alloys. It is anticipated that the results derived from this project will 1) quantify the resistance of grain boundaries to short fatigue crack growth, 2) identify the optimum texture that leads to the more balanced mechanical properties, especially the fatigue properties, and 3) develop a 3D model for better simulation of short crack growth hence improving the methodology for life prediction of key engineering components. NON-TECHNICAL: Quantitative understanding of the interaction of a short fatigue crack with grain boundaries is critical to design of safer engineering structures such as airplanes and spacecrafts, and for more sustainable use of materials. In this project, the research work will be integrated into the PI's teaching activities, and the findings from this research project will also be utilized to promote materials education. A new course on crystallographic texture aimed at upper level undergraduate students and beginning graduate students will be developed to bridge the gap between extensive research and insufficient education in the field of texture. Currently, few universities offer such as a course in the U.S. In addition to graduate students, undergraduate students will also be trained in texture theory and research by participating in experimental and theoretical activities in this project. As an outreach activity in this project, the PI will also develop an on-line self-study course on texture in order to promote education on texture beyond the PI's university and help to train the technical personnel in materials industry about texture and the importance of its control during processing of metallic materials. Feedback about these courses will be actively sought and used to further improve the effectiveness of these courses.