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oai:www.ideals.illinois.edu:2142/50624 2023-07-11 col_2142_5131 col_2142_14787 com_2142_5130 com_2142_9630 com_2142_234

Beaudoin, Armand J. Chatterjee, Kamalika 2014-09-16T17:24:28Z 2014-09-16T17:24:28Z 2014-08 2014-09-16 2014-08 A new approach for lattice strain determination is proposed for analysis of three dimensional x-ray diffraction (3DXRD) data. Our objective is to establish a correspondence between lattice strain and change of diffraction spot position in $\omega$ ($\omega$ is the rotation angle about the loading axis for 3DXRD experiment), using far-field configuration. The final goal is to apply the same concept to extract subgrain level strain from near-field data (near-field has less resolution in 2$\theta$. $\theta$ is the scattering angle for diffraction). The method is developed using the far-field 3DXRD data obtained from an \textit{in-situ} experiment of a Ti-7Al alloy sample. The experiment is conducted at beamline- 1 ID of the Advanced Photon Source at Argonne National Laboratory. A high-resolution monochromator is used to get high strain resolution. The specimen is subjected to combined bending and uniaxial tensile loads up to yield at highest local stress points.  Far-field images are collected in two ways- (a) at each $0.5^o$ rotation about the loading axis from $-180^o$ to $180^o$ (coarse scan),(b) at each $0.05^o$ rotation about the loading axis from $-180^o$ to $0^o$ (fine scan). A near-field data collection is carried out simultaneously. A study of the stress gradient developed in the Ti-7Al sample is performed using lattice strain determination algorithm taking care of the grain precession. A map of grain orientation in the cross-section of the sample is determined through use of the near-field technique. A state of bending with superposed tension is revealed through correlation of the near-field grain map with the far-field strain and center of mass (COM) result. Lattice strain induced changes of $\omega$ are found for all scattering vectors of individual grains. It is plotted against the final $\omega$ positions of the scattering vectors. Such plots are generated for every individual grain indexed by \textit{GrainSpotter}. The theoretically determined values of change of $\omega$ ($\Delta\omega_{model}$) follow a sinusoidal pattern when plotted against the final $\omega$ positions (the effect of grain precession on lattice strain is taken care of in the theoretical calculations). The experimentally found values of change of $\omega$ ($\Delta\omega_{meas}$ or $\Delta\omega_{log}$) may or may not show the similar coorespondence depending on the lattice orientation and lattice strain. The magnitude of the $\Delta\omega_{model}$ is found to be lower than the magnitude of the $\Delta\omega_{meas}$ or $\Delta\omega_{log}$. The fine scan proves to be more informative than the coarse scan for study of shift of $\omega$ position of a diffraction spot with change of load. Item withdrawn by Laura Spradlin (lspradl2@illinois.edu) on 2014-07-18T16:33:59Z Item was in collections: University of Illinois Theses & Dissertations (ID: 1) No. of bitstreams: 1 Chatterjee_Kamalika.pdf: 16339065 bytes, checksum: 9f4d8ad2edc123d6c938068bc0f57938 (MD5) Made available in DSpace on 2014-09-16T17:24:28Z (GMT). No. of bitstreams: 2 Kamalika_Chatterjee.pdf: 16338423 bytes, checksum: f0ee2962884a547563a65d8ef7092d88 (MD5) license.txt: 4069 bytes, checksum: 3ed5376a096ad88d538b75f990e25c37 (MD5) http://hdl.handle.net/2142/50624 en Copyright 2014 Kamalika Chatterjee x-ray diffraction far-field near-field high resolution monochromator lattice strain center of mass grain map diffraction spot position bending trend Determination of grain-level strain and proposing a new method of strain determination for three dimensional x-ray diffraction (3DXRD) text Mechanical Sci & Engineering 1917 Mechanical Engineering 0133 University of Illinois at Urbana-Champaign Thesis M.S. MS:Mechanical Engineerng -UIUC 10KS0133MS