Measuring Stress Distributions in Ti-6Al-4V Using Synchrotron X-Ray Diffraction
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developed synchrotron X-ray diffraction techniques are changing the manner in which we test the microstructure and, indeed, the micromechanical state within deforming polycrystalline metallic specimens. The combination of rapid collection times and the ability to observe many scattering vectors simultaneously facilitates the performance of thermomechanical processing and performance-like experiments in situ. Experimental techniques have been developed toward this end, to observe both ‘‘bulk’’ populations[1–3] and individual embedded grains.[4–7] The data from such experiments can provide an unparalleled level of detail regarding the evolution of micromechanical states during deformation processes. Perhaps the most important product from these experiments is the increased understanding of grain-scale J.V. BERNIER, Postdoctoral Fellow, is with the Materials Modeling and Simulation Group, Engineering Technologies Division, Lawrence Livermore National Laboratory, Livermore, CA 94550. J.-S. PARK, Graduate Research Assistant, and M.P. MILLER, Professor, are with the Sibley School of Mechanical and Aerospace Engineering, Cornell University, Ithaca, NY 14853. Contact e-mail: [email protected] A.L. PILCHAK, Graduate Research Assistant, is with Department of Materials Science and Engineering, The Ohio State University, Columbus, OH 43210. M.G. GLAVICIC, Senior Materials Fellow, is with Rolls Royce Corporation, Indianapolis, IN 46206-0420. This article is based on a presentation given in the symposium entitled ‘‘Neutron and X-Ray Studies for Probing Materials Behavior’’ which occurred during the TMS Spring meeting in New Orleans, LA, March 9–13, 2008, under the auspices of the National Science Foundation, TMS, the TMS Structural Materials Division, and the TMS Advanced Characterization, Testing, and Simulation Committee. Article published online October 15, 2008 3120—VOLUME 39A, DECEMBER 2008
deformation partitioning. The measured distributions of crystal (lattice) strains and the related stresses describe the micromechanical state and can be employed to understand important phenomena such as crack initiation and phase transformation. At the scale of statistically representative volumes, these distributions are expected to display a nontrivial orientation dependence. Furthermore, the crystal strains/stresses may in general be quite different from the macroscopic quantities; as such, maximizing the number of independent strain measurements is generally necessary, to best quantify the micromechanical state. Motivated by quantitative texture analysis (QTA), our group has developed a synchrotron X-ray diffraction method for measuring lattice strain pole figures (SPFs). The challenge of such quantitative strain analysis (QSA) experiments is to maximize the number of SPFs measured and the amount of data on each. By employing in-situ mechanical loading, sets of SPFs are acquired at various macroscopic stress values.[3] The SPF data from a polycrystalline aggregate are inverted to form a lattice strain distribution function (LSDF), which i
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