Basic stress-strain principles of elasticity theory are related to elastic strains that could occur in metals and alloys. The equated relationships are expressed as a function of the diffraction line shift that occurs because of a variation in the spacing d of the atomic planes in a crystalline material that is due to applied or residual stress. This fractional change in d is a strain from which stress can be calculated and which can be determined by the change of angular position of a diffracted x-ray beam.
