Auto-calibration principles for two-dimensional residual stress measurements by Barkhausen noise technique

The magnetic Barkhausen Noise (BN) is well suited to evaluate the effects of mechanical stresses of ferromagnetic materials, e.g. the indirect detection of residual stress states. The most common causes for the occurrence of residual stresses are manufacturing processes, such as casting, welding, machining, forming, heat treatment, etc., consecutive repairs and design changes, and installation or assembly and overloads during the operating life of a construction. A significant calibration effort based on a set of reference values and/or test samples is needed for these measurements, which require a great deal of time and material resources. Additionally, it is impossible to determine the stress states of different components (s xx and s yy ) at the surface. Therefore, a new auto-calibration method was developed to analyze two-dimensional stresses. A fixed calibration function based on defined parameters (determined experimentally) was applied. To adjust the auto-calibration function to the experimental reference values by varying functional parameters, a large number of measurement points were used. We present a method that can calculate, based on the multi-dimensional stress state at the measuring point, the stress components s xx and s yy for two perpendicular magnetization directions using the Barkhausen Noise effect.