Residual stresses can be measured non-destructively with X-ray diffraction method. X-ray diffraction provides reliable and objective data for quality control assessment.
X-rays have high energy and short wavelength when compared to visible light making them ideal for probing the interplanar distances (=residual stress) in crystalline materials.
Barkhausen noise analysis is a non-destructive method involving the measurement of a noise like signal induced in a ferromagnetic material by an applied magnetic field.
There are two main material characteristics that will directly affect the intensity of the Barkhausen noise signal: hardness and stress.
In ESPI hole drilling method stressed material is removed by drilling a small blind hole in the area of interest and the material around the hole spontaneously finds a new stress equilibrium. This leads to a displacement of the surface near the hole which is traditionally measured using strain gauges. These displacements are measured by using optical interferometry. The measured displacements are then used to calculate stresses which existed in the volume prior to drilling.