Patent ID: 6874369

Claim:
A stress measurement method using X-ray diffraction, comprising the steps of: (a) preparing a c-axis-oriented specimen of a tetragonal polycrystal as a specimen to be measured; (b) defining, as a specimen coordinate system, a coordinate axis P 3 perpendicular to a surface of the specimen and two coordinate axes P 1 and P 2 orthogonal to each other within the specimen surface, and arranging an X-ray optical system including an X-ray source and an X-ray detector within a plane including the coordinate axes P 1 and P 3 ; (c) selecting one set of Miller indices (hkl) of the specimen, and arranging the X-ray source and the X-ray detector to be symmetrical with a normal to a crystal plane with said one set of Miller indices (hkl), the normal to the crystal plane being inclined from a normal to the specimen surface at an angle of ψ, so that a diffracted X-ray from the crystal plane with said one set of Miller indices (hkl) can be detected with a diffraction angle θ 0 (diffraction angle in a non-strain state); (d) irradiating the specimen with an X-ray, detecting the diffracted X-ray therefrom with the X-ray detector, adjusting the X-ray optical system to find out the diffraction angle θ at which the diffracted X-ray exhibits a maximum intensity, and determining the diffraction angle θ as a measurement value; (e) determining a strain through the use of the diffraction angle θ 0 in the non-strain state and the diffraction angle θ measured; (f) selecting another set of Miller indices (hkl) of the specimen, repeating the above-described steps (c) to (e), and determining a strain with respect to said another set of Miller indices (hkl); (g) arranging the X-ray optical system including the X-ray source and the X-ray detector within a plane which is derived by rotation of the plane including the coordinate axes P 1 and P 3 around the coordinate axis P 3 through an angle of φ=45°; (h) repeating the above-described steps (c) to (f); (i) arranging the X-ray optical system including the X-ray source and the X-ray detector within a plane which is derived by rotation of the plane including the coordinate axes P 1 and P 3 around the coordinate axis P 3 through an angle of φ=90°; (j) repeating the above-described steps (c) to (f); and (k) determining a stress σ 11 in a direction of the coordinate axis P 1 , a stress σ 22 in a direction of the coordinate axis P 2 and a shearing stress σ 12 between the coordinate axes P 1 and P 2 based on the strain ε (φ=0°) determined in the above-described step (f), the strain ε (φ=45°) determined in the above-described step (h), the strain ε (φ=90°) determined in the above-described step (j) and sin 2 ψ through the use of stress calculation formulae determined under the conditions of a plane stress state and a symmetry 4/mmm.