Even though most metals exhibit isotropic properties on a macroscopic scale, they are inherently anisotropic on the mesoscale – or grain size scale – due to elastic and plastic anisotropy in the single crystal properties. The elastic anisotropy is given by the single crystal elastic constants and the plastic anisotropy is dictated by the available plastic deformation modes, e.g. slip and twinning systems. Neutron diffraction offers a unique ability to directly measure the anisotropic behavior of crystalline materials. As all diffraction techniques, it relies on measuring lattice plane distances in the grains, and thereby allows for measurement of elastic lattice strains. The great advantage of neutron diffraction – compared to conventional X-ray diffraction – is the large penetration depth of neutron that enable true bulk measurements through centimeters of materials such as aluminum and steel. The diffraction technique is phase and orientation specific which makes it ideal to investigate the anisotropic behavior of materials and composites. However, the specificity of the technique also makes it non-trivial to convert the measured data into a macroscopic response, and the use of polycrystal deformation models to has proven a useful tool in analyzing the data. At the same time the neutron diffraction measurements are ideal for validating the polycrystal deformation models as it enables direct comparison of elastic strains on the grain level, which is the basis of the models. Examples of measurements and model predictions will be given.
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