Development of the magnescope as an instrument for in situ evaluation of steel components of nuclear systems

Abstract

Fatigue damage causes continuous, cumulative microstructural changes in materials and the magnetic properties of steels are sensitive to these microstructural changes. The work therefore focused on the relationship between fatigue damage and the measured magnetic properties of different steels under a variety of fatigue conditions. The project also investigated the feasibility and applicability of magnetic inspection techniques for non-destructive evaluation of fatigue damage. From the results of a series of fatigue tests, conducted on different steels under both low-cycle and high-cycle fatigue conditions, the magnetic properties, such as coercivity, remanence and Barkhausen effect, were found to change systematically with fatigue damage. The magnetic properties showed significant changes, especially during early stage of the fatigue and also at the end of the fatigue lifetime. An approximately linear relationship between the mechanical modulus and magnetic remanence was observed and was explained by a model developed in this study to describe the dynamic changes in magnetic and mechanical properties. The results of this research demonstrated that magnetic measurements are suitable for non-destructive evaluation of fatigue damage in steels such as A533B steel and Cr-Mo steels. The magnetic measurement techniques have been incorporated into instrumentation for in-situ evaluation of steel structures and components.