Fatigue damage causes nano- and micro-structural changes in metals that ultimately cause structures to fail. While materials characterization techniques can classify this damage at very small scales, measuring such changes while damage is occurring and in large-scale samples remains a challenge. This award supports fundamental research to address these challenges by studying how nonlinear high-frequency waves propagate in metals undergoing fatigue damage. This knowledge will not only improve our understanding of how damage such as fatigue evolves, it will also provide important insight into how high-frequency waves propagate in metals. Because many structures and materials undergo fatigue, it will benefit society by improving the safety and efficiency of structures, such as those used in airframes, transportation systems, and energy infrastructure. This award will also support student education in critical engineering skills at multiple levels, through an integrated K-12 outreach program that incorporates a project-based undergraduate course and graduate student mentors.
The objective of this project is to determine the relationship between nonlinear high-frequency wave propagation and dislocation-based damage at the mesoscale. To do this, nonlinear wave measurement techniques and models will be integrated with digital image correlation, electron backscatter diffraction, and scanning electron microscopy, to characterize cyclic loading of polycrystalline FCC material. Spatial variations in dislocation-based damage will be captured and correlated with nonlinear high-frequency wave measurements and used to predict fatigue damage. A new constitutive relationship will be introduced relating the acoustic nonlinearity parameter measured by ultrasound and accumulated strain that captures dislocation-based damage at the mesoscale measured with digital image correlation. Finally, nonlinear ultrasound will be used to spatially characterize dislocation parameters throughout the fatigue life of samples, and then used to validate or update micromechanical models for fatigue evolution in polycrystalline metal. This fundamental knowledge will uncover how dislocation-based damage manifests at the mesoscale, how this relates to fatigue evolution, as well as how nonlinear high-frequency waves propagate through spatially heterogeneous nonlinear elastic media.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
