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The Determination of Single Crystal Elastic Moduli From Powder Diffraction Experiments. Thomas Gnäupel-Herold^1,2, Paul C. Brand¹ and Henry J. Prask¹, ¹National Institute of Standards and Technology, Center for Neutron Research, Gaithersburg, MD 20899 USA, ²University of Maryland, Department of Materials and Nuclear Engineering, College Park, MD 20742-2115 USA

A wide area of material science is concerned with the elastic properties of crystalline materials. While the description of the elastic constants is often sufficient in terms of the isotropic Young's modulus E and Poisson's ratio [nu], there is also a variety of cases in which the anisotropic properties of crystal elasticity are of interest. The most common method for the determination of the single-crystal stiffnesses c_ijkl is ultrasonic resonance, which is, however, limited to single crystals of sufficient size. Very recently a completely new approach has been developed [1] which utilizes the diffraction elastic constants for the subsequent calculation of the single crystal elastic constants. The concept of the measurable, hkl dependent diffraction elastic constants describes the fact that diffraction methods on polycrystalline aggregates select a group of suitably oriented crystallites out of the polycrystal, so that information of partia

In particular, the theory is based upon an appropriately defined function, which allows for the calculation of the diffraction elastic constants from an estimated set of c_ijkl. This estimate is then refined in a LS process which fits the calculated diffraction elastic constants to the measured ones, and the c_ijkl are the free parameters of the LS process. Utilizing neutron diffraction this approach has been succesfully applied to a number of materials, some of which allowed the comparison to results obtained by other methods.

[1] Gnäupel-Herold, T., Brand, P. C., Prask, H. J., (1998). to be submitted to J. Appl. Cryst.