Residual stresses affect such important materials design properties as fatigue life, fracture strength, onset of yield, and microcracking. Of all the residual stress measuring techniques, neutron diffraction methods are widely accepted as the most general and reliable nondestructive method of quantifying the residual stress tensor. Neutron diffraction methods use the atomic planes of the crystalline grains within the material as very sensitive strain sensors. Analysis techniques permit separation of long range macrostresses and short range or grain-to-grain microstresses.  Crystallographic texture, or the non-random orientation of grains, is also measured for correlation with materials performance. 

In x-ray and neutron diffraction, polycrystalline solid or powdered specimens are placed in a monoenergetic, collimated beam. Appropriately oriented grains diffract the x-rays or neutrons into a detector. By sweeping the angle of incidence and detection, a spectrum of diffraction peaks corresponding to the crystal lattice spacings is produced. The measured lattice spacings are compared with spacings of known compounds to identify the crystalline phases and are used to refine the unit cell parameters. Analysis of unit cell parameters as a function of temperature yields the lattice thermal expansion. Reactions, phase transformation, and crystallization are all studied by high temperature diffraction methods. Crystal structure analysis (e.g. atomic location, thermal motion, site occupancy) utilizes both the line position and intensity.