  A novel original method of determination of stresses and critical resolved
shear stresses (CRSSs) using neutron diffraction was proposed. In this method,
based on the crystallite group method, the lattice strains were measured in
different directions and using different reflections hkl during uniaxial
deformation of magnesium alloy AZ31. The advantage of this method is that the
stresses for groups of grains having similar orientations can be determined
directly from measurement without any models used for data interpretation. The
obtained results are unambiguous and do not depend on the models assumptions as
in previous works. Moreover, it was possible for the first time to determine
the uncertainty of the measured CRSS values and local stresses at groups of
grains. The used methodology allowed for the determination of stress
partitioning between grains having different orientations and for an
explanation of the anisotropic mechanical behaviour of the strongly textured
alloy. Finally, the CRSS values allowed for the validation of the type of
intergranular interaction assumed in the elastic-plastic self-consistent model
and for a significant reduction of the number of unknown parameters when the
model is adjusted to the experimental data.
