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观力学状态的演变。在这些测试中，将在循环加载期间测量晶格应变，并将开发一种方法，用于在许多不同的晶格平面族的广阔的X射线散射方向上获得应变。这些数据对于开发称为数字材料的模拟环境至关重要通过与X射线检测技术前沿的研究人员（康奈尔大学的Sol Gruner教授小组）合作，将进行一组独特的高时间分辨率原位实验，这些实验将具有微秒级的曝光。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”，这将在金属颗粒的尺寸尺度上创建与演变的机械状态的“真实的时间”链接-正是我们开始理解微裂纹萌生所需要的。该项目将开始通过检查模型铁/铜合金-理想的这项研究，由于他们的相互不溶性和明显的属性差异，但最终将集中在几个铝/铍合金-这也是几乎不溶。此外，这些材料的衰减长度比Fe/Cu小得多，因此更厚的样品（对于循环实验至关重要）和更低的X射线能量将是可能的。这个项目的教育目标是使机械工程师能够在材料工程竞技场中运用他们的设计训练。这个项目还将大大扩展大多数工程专业学生拥有的传统实验曲目。从事这个项目的学生将学会把同步加速器光束线这样的设施看作是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造Al/Be样品。将产生几种相分数的合金。实验计划是材料表示系统的一个方面，被称为康奈尔数字材料。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.