Residual stress is considered the “fingerprint” of metal components and their technological history.
They are used both for research and for the optimization of the processes both as control of the processes themselves and for a better guarantee of repeatability and constancy of the processes in time.
XRD (X Ray Diffraction)
The XRD (X Ray Diffraction) technique, uses the diffraction of x rays on metals. It is a versatile, non-destructive analytical technique by means of which it is possible to study the structural characteristics of metals. Metals are made up of crystals whose atoms occupy well established positions in the reticular structure. An x ray beam is projected onto the surface of the component, the beam penetrates for a few micrometers into the metal, hits the atoms of the lattice which is “reflected” with characteristics that depend on the tensional condition of the metal itself. Through a mathematical elaboration, we obtain the residue tension ration that is present on the surface of the component.
BHD (Blind Hole Drilling)
The BHD (Blind Hole Drilling) technique uses a strain gauge rosette at the center of which we make a calibrated hole. After the hole, the residual stress that are present on the material relax. The strain gauges of the rosette get the deformations provoked by the relaxation that, re-elaborated, are translated into residue tensions through the theory of elasticity. It is a mini-destructive technique that makes a little hole about 2mm in diameter and 1-2 mm in depth. The strength of the BHD is that it can be applied to any kind of material, not necessarily metal ones. It can be used in synergy with XRD to obtain residue tension profiles with very deep exploration levels.