Evaluation of changes in microstructure and mechanical performance of metals via electrical resistivity measurements

This work focuses on experimental study of cross-property connections that link up effective linear elastic and electrical conductive properties of heterogeneous materials. Such connections are especially useful when one property (electrical conductivity) is easier to measure than the other (elastic constants). Also, take advantages from the easy of measure electrical resistance to study the microstructural changes, and then compare results with different methods like microscopy and other published methods. Mechanical and electrical properties of different specimens under both fatigue and quasi-static loading were investigated, combined with the analysis of microstructural changes produced by such loading. Two different types of metals (stainless steel 304 and Titanium CP-2) have been cut from sheets and then subjected to two different type of loading: cyclic loading (up to 80000 cycles) at several values of maximal stress sigmamax and then quasi-static loading. At low values of sigmamax 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 sigmamax grow up, reduction in Young's modulus and in ultimate strength of the specimens take 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 sigma max. (higher than the yield limit) follow the theoretically predicted cross-property connection for microcracked materials. Qualitative correlation between strength reduction and maximum value of local resistivity across the specimen has been observed at qualitative level.