CAREER: Kinematics of Stage II Fatigue Crack Propagation

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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.***