Forward Model Based Strain Analysis in Highly Deformed Metallic Systems Using Electron Back-Scatter Diffraction Patterns

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NON-TECHNICAL SUMMARYThe use of metals and alloys in engineering applications requires a thorough understanding of how these materials will behave when they are subjected to stresses that cause them to deform. Although the deformations can sometimes be visible to the naked eye, the actual deformation processes take place at very small length scales, which necessitates the use of electron microscopes operated at high magnification. This research will develop a new experimental technique to measure these deformations with high accuracy. Such detailed measurements will contribute to our understanding of how materials deform, and, ultimately, this will impact how metals and alloys can be used safely in structural applications throughout society. All techniques developed in this program will be made available to the community through publications and in the form of open source code. The PI will also explore the possibility of generating free college-level text books via a crowd-sourcing approach; this "OpenChapters" project will combine individual chapters written by multiple authors into customizable on-demand text books that will be freely available to college students as well as to society at large.TECHNICAL SUMMARYModern engineering materials often have a complex multi-phase microstructure that makes it difficult to accurately predict how they will behave under the influence of an applied stress. Many aspects of the deformation behavior of a material are still poorly understood. The extraction of lattice strains from deformed polycrystalline samples is a difficult undertaking that requires renewed attention due to the availability of new detector systems, in particular for electron back-scattered diffraction (EBSD), the tool of choice for the proposed program. The PI and his group will employ a physics-based model for the prediction of EBSD patterns and incorporate a new capability to include the deformation tensor in the pattern generation algorithm. In combination with a recently developed indexing algorithm, a new approach will be developed to determine the deformation tensor components by matching complete simulated EBSD patterns against their experimental versions, with an anticipated strain resolution of better than 0.0001 over large sample areas. This program has the potential to advance our understanding of micro- and nano-scale mechanisms of deformation in modern engineering materials as well as in lower symmetry geological samples. The combination of sensitive EBSD detectors with a modified indexing scheme will lay the foundation for the routine determination of strain fields by full-pattern matching of EBSD data. The algorithms will be made available to the community in peer-reviewed publications and as open source code. On the educational side, the OpenChapters project will address the rapidly rising cost of text books by creating an open source mechanism for the generation of free text books by a crowd-sourcing approach.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.