A Methodology for Designing Fatigue Resistant Materials

该研究项目围绕着一套新颖的原位机械加载/同步加速器x射线衍射实验，旨在了解多相金属合金中与微裂纹萌生相关的微力学状态的演变。在这些测试中，晶格应变将在循环加载期间进行测量，并将开发一种方法，用于在许多不同晶格平面家族的大量x射线散射方向上获得应变。这些数据对于被称为数字材料的模拟环境的发展至关重要。通过与研究x射线探测技术前沿的研究人员（康奈尔大学索尔·格鲁纳教授的小组）的合作，将进行一套独特的高度时间分辨的原位实验，这些实验将以微秒的顺序进行曝光。通过在几千个循环中的几个循环中进行曝光，将有可能在循环加载期间产生晶格应变“快照”，这将创建一个与金属颗粒尺寸尺度上不断变化的机械状态的“实时”链接——这正是我们开始理解微裂纹萌生所需要的。该项目将首先检查模型铁/铜合金——由于它们相互不溶性和明显的性能差异，这是本研究的理想选择，但最终将集中在几种铝/铍合金上——它们实际上也不溶性。此外，这些材料的衰减长度比Fe/Cu小得多，因此更厚的样品（对循环实验至关重要）和更低的x射线能量将是可能的。该项目的教育目标是使机械工程师能够在材料工程领域运用他们的设计培训。这个项目也将极大地扩展大多数工科学生所拥有的传统实验曲目。在这个项目中工作的学生将学会将同步加速器束流线等设施视为进行标准表征实验的地方。Brush Wellman公司和洛斯阿拉莫斯国家实验室将与康奈尔大学合作制作人工智能/Be样本。将生产几种相分数的合金。实验程序是被称为康奈尔数字材料的材料表示系统的一个方面。该项目将启动数字材料表示的创建，旨在加速抗疲劳材料的设计和实施。

This research project is centered around novel sets of in-situ mechanical loading / synchrotron x-ray diffraction experiments aimed at understanding evolving micromechanical states associated with microcrack initiation in multiphase metallic alloys. In these tests, lattice strains will be measured during cyclic loading and a methodology will be developed for attaining strains over a vast expanse of x-ray scattering directions for many different families of lattice planes. These data are crucial to the development of a simulation environment referred to as the Digital Material Through a collaboration with researchers working at the forefront of x-ray detection technology (Professor Sol Gruner's group at Cornell), a unique set of highly time resolved in-situ experiments will be conducted that will have exposures on the order of microseconds. By taking exposures over several cycles out of several thousand cycles, it will be possible to produce lattice strain "snapshots" during cyclic loading, which will create a "real time" link to the evolving mechanical state on the size scale of a metallic grain - exactly what we need to begin to understand microcrack initiation. The project will begin by examining model iron / copper alloys - ideal for this study due to their mutual insolubility and distinct property differences, but will eventually center on several Aluminum/Beryllium alloys - which are also virtually insoluble. In addition, the attenuation lengths for these materials are much smaller than the Fe/Cu so a thicker specimen - crucial for cyclic experiments - and lower x-ray energies will be possible. The educational goals of this project are based on enabling mechanical engineers to employ their design training within the materials engineering arena. This project will also greatly expand the conventional experimental repertoire that most engineering students possess. The students working on this project will learn to think of facilities like synchrotron beam lines as a place to conduct standard characterization experiments. The Brush Wellman company and Los Alamos National labs will partner with Cornell in the fabrication of the Al/Be specimens. Alloys at several phase fractions will be produced. The experimental program is one aspect of the material representation system referred to as the Cornell Digital Material. This project will initiate the creation of a Digital Material representation aimed at accelerating the design and implementation of fatigue resistant materials.