A Critical Evaluation of the Norelco High Angle X-Ray Spectrometer for Elastic Strain Measurements

Abstract

The theory of measuring elastic strains in metals with an x‐ray spectrometer is discussed and comparison is made with the x‐ray back‐reflection film method. It is shown that the accuracy attained in the determination of the surface biaxial stress sum from measurements on sharp diffraction lines with the spectrometer is equally as good as, or better than, that attained with the usual film techniques. An example is given of the determination of the biaxial stress sum with the spectrometer in a steel hardened to Rockwell C55. It was not possible to make the same determination photographically. The effect of elastic anisotropy on x‐ray stress determinations is briefly discussed. It is shown that the error in the determination of the stress sum due to an improper choice of elastic constants is less than that due to the normal experimental errors. An example is given of an x‐ray determination of Poisson's ratio in different crystallographic directions in a FS8742 steel.