CAREER: Kinematics of Stage II Fatigue Crack Propagation

这个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中疲劳裂纹扩展的动力学。对疲劳裂纹扩展的塑性钝化过程进行了量化，将裂纹尖端塑性变形的运动学与新断口的产生联系起来。采用云纹干涉技术和原子力显微镜(AFM)原位测试技术相结合的方法，测量了具有标准几何形状的样品中疲劳裂纹尖端周围位移场的演化。确定了导致裂纹扩展的应变场分量，并将其量化为外加载荷的函数。单相金属材料的单晶和多晶最初被用来避免可能掩盖塑性变形对裂纹扩展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)，研究了滑移模式(波状或平面)的影响。利用取向成像显微镜(OIM)与洛斯阿拉莫斯国家实验室合作，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。这位研究人员在亚利桑那州立大学的第一年与本科生建立了组装激光干涉仪、图像采集、现场测试和其他数据收集系统的项目。本科生参与研究是该项目教育方面的一个基本部分。他们将被指导创造工具，可以用来进行研究，并在本科生实验室中演示疲劳的原理。此外，将对现有的材料力学本科实验和课程进行修改，并开设新的技术选修课，以增加学生接触疲劳和断裂现象以及变形和断裂评估的非破坏性技术的机会。这些本科生和研究生级别的选修课将提供来自研究项目的材料以及实际的工程应用。尽管塑性钝化过程被认为是疲劳裂纹扩展的基本机制，但这一信息在延性材料的开放文献中尚不存在。收集的数据将被用来寻找裂纹推进和所施加的载荷之间的联系，并将寻求与线弹性断裂力学(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.***