Estimation of changes in the mechanical properties of stainless steel subjected to fatigue loading via electrical resistance monitoring

The paper focuses on experimental study of mechanical and electrical properties of fatigued specimens combined with the analysis of microstructural changes produced by cyclic loading. The specimens have been cut from stainless steel 304 and subjected to cyclic loading (up to 80,000 cycles) at several values of maximal stress σmax. At low values of σmax as well as at the low number of cycles no significant changes in mechanical properties and mild decrease in electrical conductivity (approximately uniform over the specimen) have been observed. The latter can be explained by generation cluster of new dislocations that can be seen in photo images in the form of black dots. As the number of cycles and σmax grow up, reduction in Young’s modulus and in ultimate strength of the specimens takes place. This reduction is accompanied by local decrease in electrical conductivity due to formation of the microcracks. Changes in Young’s modulus and electrical conductivity at high values of σmax (higher than the yield limit) follow the theoretically predicted cross-property connection for microcracked materials. Correlation between strength reduction and maximum value of local resistivity across the specimen has been observed at qualitative level.