CAREER: Kinematics of Stage II Fatigue Crack Propagation

9984633Peralta该实验计划的主要研究目标是找到一种替代方法来预测单相金属材料的疲劳裂纹扩展动力学。将疲劳裂纹扩展的塑性钝化过程定量化，将裂纹尖端的塑性变形运动学与新断裂面的产生联系起来。在具有标准几何形状的样品中疲劳裂纹尖端周围的位移场的演变是通过以下技术的组合来测量的：用于整体场的莫尔干涉法和用于近尖端行为的原子力显微镜（AFM）中的原位测试。负责裂纹前进的应变场的组件被确定和量化的功能所施加的载荷。最初使用单相金属材料的单晶和多晶，以避免可能掩盖塑性变形对裂纹生长动力学的影响的额外损伤机制。通过选择具有高、中、低层错能的材料（Al、Ni和黄铜）来研究滑移模式（波状或平面）的影响。与洛斯阿拉莫斯国家实验室合作，用取向成像显微镜（OIM）研究了多晶体中局部晶体织构产生的各向异性的可能影响。研究员已经建立了与本科生的项目，组装激光干涉仪，图像采集，原位测试和其他数据收集系统在他的第一年在亚利桑那州立大学。本科生参与研究是该计划教育方面的基本组成部分。他们将被引导创建可用于进行研究的工具，并在本科实验室中展示疲劳的原理。此外，目前的本科实验室和材料力学课程将进行修改，并创建新的技术选修课，以增加学生对疲劳和断裂现象的接触，以及对变形和断裂评估的非破坏性技术。这些本科和研究生级别的选修课将提供来自研究计划以及实际工程应用的材料。尽管塑性钝化过程被认为是疲劳裂纹扩展的基本机制，但在韧性材料的公开文献中还没有这方面的信息。收集的数据将用于寻找裂纹扩展和所施加载荷之间的联系，并寻求与线性弹性断裂力学（LEFM）的相关性。*

9984633PeraltaThe main research goal of this experimental program is to find an alternative approach to predict the kinetics of fatigue crack growth in one-phase metallic materials. The plastic blunting process of fatigue crack growth is quantified to relate the kinematics of plastic deformation at the crack tip to the creation of new fracture surface. The evolution of the displacement fields around fatigue crack tips in samples with standard geometries is measured by a combination of techniques: Moire Interferometry for the overall fields and in-situ testing in an Atomic Force Microscope (AFM) for the near-tip behavior. The components of the strain field responsible for crack advance are identified and quantified as functions of the applied loads. Single crystals and polycrystals of one-phase metallic materials are used initially to avoid additional damage mechanisms that could mask the effects of plastic deformation on the crack growth kinetics. The effect of slip mode (wavy or planar) is studied by selecting materials with high, medium and low stacking fault energy (Al, Ni and brass). The possible effect of anisotropy produced by local crystallographic texture in polycrystals is studied by Orientation Imaging Microscopy (OIM) in collaboration with Los Alamos National Laboratory. The investigator has established projects with undergraduate students to assemble the laser interferometer, image acquisition, in-situ testing and other data gathering systems during his first year at ASU. The involvement of undergraduates in the research is a fundamental part of the educational aspect of this program. They will be directed to create tools that can be used to perform research and to demonstrate the principles of fatigue in undergraduate laboratories. In addition, current undergraduate labs and courses in mechanics of materials will be modified and new technical electives created to increase the exposure of the students to fatigue and fracture phenomena as well as to non-destructive techniques for deformation and fracture evaluation. These electives at the undergraduate and graduate levels will offer material derived from the research program as well as practical engineering applications. %%%This information is not yet available in the open literature for ductile materials, despite the acceptance of plastic blunting process as a fundamental mechanism of fatigue crack growth. The data collected will be used to find a connection between the crack advance and the applied loads and correlations with Linear Elastic Fracture Mechanics (LEFM) will be sought.***