Nondestructive Analysis of Stress States in Components using Micromagnetic and Ultrasonic Techniques - An Overview

The application of electromagnetic, magneto-elastic techniques is recommended if stresses or stress gradients in surface near layers are of interest. The use of one measuring quantity allows the evaluation of stress states in parts with a controlled microstructure. The combined use of different electro-magnetic and magneto-elastic quantities enables the evaluation of stress states of parts with an inhomogeneous microstructure and characterization of microstructural states in terms of hardness of strength values. Consequently, the main application is to characterize stress and microstructure in mechanically or thermally treated surfaces of technical parts. The set-ups available on the market mainly differ in the measuring quantities used. In all cases, the quantities have to be calibrated using samples with a known microstructural state. The major area of ultrasonic applications covers the analysis of stress states in surface layers of about 5mm of thickness and of stress states in the bulk of large components. The quantitative stress analysis presumes the knowledge of the material dependent elastic properties. Set-ups optizmized of the evaluation of stress states of bolts and screws, of railroad wheels and rails are on the market. Different laboratory prototypes are in use to evaluate stress states of specific components