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

技术：这项职业计划致力于研究晶界对短疲劳裂纹扩展的抵抗力，以及晶体织构和晶粒结构对高性能合金疲劳性能的影响。目前，在计算疲劳短裂纹扩展时，现有的模型都不能考虑微观组织的三维效应，因而其成功程度有限。这项研究建立在PI最近成功地确定了晶界裂纹面偏转的扭曲和倾斜分量作为控制跨晶界短裂纹扩展行为的关键因素的基础上。为了揭示裂纹平面偏转与裂纹扩展阻力之间的定量关系，本研究将对一种具有细微缺口的单晶合金进行独特设计的疲劳试验。用电子背散射衍射法详细研究了织构对不同织构的新一代高强铝合金疲劳性能的影响。所有这些实验得到的数据将被用来建立一个三维模型，通过考虑晶界和裂纹之间的三维相互作用以及合金中织构的影响来量化疲劳短裂纹的扩展行为。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)确定导致更平衡的力学性能，特别是疲劳性能的最佳织构，以及3)开发一个更好地模拟短裂纹扩展的3D模型，从而改进关键工程部件的寿命预测方法。非技术性：定量了解疲劳短裂纹与晶界的相互作用对于设计更安全的工程结构(如飞机和宇宙飞船)以及更可持续地使用材料至关重要。在这个项目中，研究工作将融入到PI的教学活动中，并将利用这个研究项目的成果来促进材料教育。将开发一门针对高水平本科生和初级研究生的晶体织构新课程，以弥合织构领域广泛研究和教育不足之间的差距。目前，美国很少有大学开设这样的课程。除了研究生，本科生还将通过参与该项目的实验和理论活动来接受纹理理论和研究方面的培训。作为这个项目的一项外展活动，国际织构协会还将开发一个关于织构的在线自学课程，以促进国际织构大学以外的关于织构的教育，并帮助培训材料行业的技术人员关于织构及其在金属材料加工过程中控制织构的重要性。我们会积极征询市民对这些课程的意见，并加以利用，以进一步提高这些课程的成效。

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.