Stress determination in metals

If a piece of metal is strained, the unit cell dimensions will be altered slightly. Because the magnitude of the cone angle of a diffraction cone is a function of the d-spacing, any small change in the d-spacing can be observed as a corresponding change in the $\theta$ angle of the diffracted cone. Thus, accurate measurement of stress can be obtained by measuring the differences in $\theta$ angles from powder (pin-hole) photographs of the specimen made before and after straining.

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