[224][225][226][227][228][229][230][231][232][233][234] for X-ray stress analysis for polycrystalline specimens with fibre texture is re-examined. By introducing the symmetry of reciprocal lattices for constituent crystallites, the physical meaning of taking an average of the strains observed by X-ray diffraction and the validity of the approximation used are made clear. By applying the present treatment to a cubic specimen in the m3m point group, hkl Bragg reflections with h 6 ¼ k 6 ¼ l split into doublets owing to the existence of crystallites with two different orientations. The formulae derived for cubic polycrystalline specimens with h111i fibre texture in the biaxial state in the Reuss model are in good agreement with those given previously. This technique is applicable to polycrystalline specimens of any symmetry with fibre texture.

Line splitting or line broadening of an X‐ray Bragg reflection owing to a three‐dimensional or biaxial load on a cubic polycrystalline specimen with 〈111〉 fibre texture has been predicted by Yokoyama & Harada [J. Appl. Cryst. (2009), 42, 185–191] if the specimen is in the symmetry of the Laue class mm. By using a TiN film specimen and a high‐precision four‐circle diffractometer with a laboratory X‐ray source, it is shown that the profile of the 420 reflection is substantially different with and without biaxial load and also depends on the measurement direction, while the profile of the 222 reflection does not change. These results are quantitatively in agreement with the theoretical prediction, although the theory is based on the Reuss model of elasticity.

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