Micromagnetic testing at Fraunhofer IZFP: Highlights and experiences of more than 3 decades of research
In the late 70ies Fraunhofer IZFP started research on micromagnetic methods, in order to develop microstructure sensitive NDT techniques for the German reactor safety research programme. Researches of IZFP investigated magnetic and acoustic Barkhausen noise analysis, incremental permeability, analysis of upper harmonics in tangential magnetic field and dynamic magnetostriction. Soon after these first investigations, researches of IZFP have recognized, that it is beneficial to combine the information content from several methods and measuring parameters. For this purpose a "combined" micromagnetic testing instrument was developed. This was the birth of the 3MA principle - the Micromagnetic Multi-parametric Microstructure and stress Analysis. Since that time, 3MA has gone through a remarkable development. Several equipment variants and a wide range of sensors have been developed, ranging from magnetic microscopes with µm resolution up to large inspection systems for in-line strip steel inspection. 3MA is versatile, this has been proved by a huge amount of reported applications. These range from fundamental studies of material's microstructure, properties and conditions to serial or even process-integrated testing of industrially produced parts in regards to hardness, residual stress, grinding burns and many more.