For precise stress analysis of engineering materials by diffraction methods, lattice spacing of strain-free materials,
d0, must be accurately measured and estimated. Powder diffraction method is a general way of determining the
d0. However, preparation of high quality powder sample is actually difficult in that labor, time, knowledge, and technique are required. In this study, we propose a new easy technique of measuring the sample as original process material instead of the powder diffraction method for estimation of accurate
d0. The
d0 obtained by our technique is estimated from the
dAve which is the average of
d measured while turning the sample material at random. The strain-free lattice constant,
a0, is calculated from
dAve(hkl) of some diffraction planes by the extrapolation method. The
d0(hkl) of each diffraction plane is converted from this
a0. In own method, the
d0(hkl) of the extra super duralumin which have the structure of the texture was measured. To examine the reliability of this new method, the
d0(hkl) obtained by own method was compared with the
d0(hkl) of powder estimated by the general methods which is neutron and X-ray diffraction method. These differences were 8.7×10
-6nm or less. These values become 10MPa or less for the stress. This result confirmed that present method could calculate
d0(hkl) with enough accuracy for the neutron residual stress analysis.
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