Stress measurement method using X-ray diffraction

A stress measurement method using X-ray diffraction, said method comprising:

• (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 P3 perpendicular to a surface of the specimen and two coordinate axes P1 and P2 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 such that a coordinate axis L3 of a laboratory coordinate system based on the X-ray optical system is within a plane including the coordinate axes P1 and P3;
• (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 about 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) is detectable with a diffraction angle θ0 (diffraction angle in a non-strain state);
• (d) irradiating the specimen with an X-ray, detecting a diffracted X-ray therefrom with the X-ray detector, adjusting the X-ray optical system to determine a 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 based on the diffraction angle θ0 in the non-strain state and the measured diffraction angle θ;
• (f) repeating steps (c) to (e) in which another set of Miller indices (hkl) is selected in step (c), and determining a strain with respect to said another set of Miller indices (hkl);
• (g) arranging said coordinate axis L3 of the laboratory coordinate system within a plane which is derived by rotating the plane including the coordinate axes P1 and P3 around the coordinate axis P3 through an angle of φ=45′;
• (h) repeating steps (c) to (f);
• (i) arranging said coordinate axis L3 of the laboratory coordinate system within a plane which is derived by rotating the plane including the coordinate axes P1 and P3 around the coordinate axis P3 through an angle of φ=90°;
• (j) repeating steps (c) to (f);
• and
• (k) determining a stress σ11 in a direction of the coordinate axis P1, a stress σ22 in a direction of the coordinate axis P2 and a shearing stress σ12 between the coordinate axes P1 and P2 based on a strain ε(φ=0°) determined in step (f), a strain ε(φ=45°) determined in step (h), a strain ε(φ=90°) determined in step (j) and sin2ψ based on stress calculation formulae determined under conditions of a plane stress state and a symmetry 4/mmm.