Automated Electrical Resistance Data Acquisition for Fatigue Deformation Detection Using a Keithley 6221 and LabVIEW

Metals are widely used in various types of structural applications, such as in the automotive, aerospace and construction industries. However, their service life is limited due to the various loads they experience during operation. Specifically, cyclic loading can lead to early fatigue failure of these structures. Therefore, early detection of fatigue deformation is essential to prevent catastrophic failures. In this study, an automated electrical resistance data acquisition system was developed using LabVIEW to obtain measurements from a Keithley 6221 current source for fatigue damage detection. The results showed an increase in electrical resistivity after the application of cyclic loading. It was observed that electrical resistivity increased after each set of loading cycles, with an average increase of 7.38% a stress level of 260 MPa (high cycle fatigue), and a 6.5% increase after the application of 25,000 cycles at 165 MPa (low cycle fatigue). Scanning Transmission Electron Microscopy (S/TEM) was used for microstuctural investigation as a proof of concept for the high-cycle-fatigue sample interrupted after 25,000 cycles to analyse the modification in dislocation structures, as well as the qualitative increment in the dislocation density with respect to the initial microstructural state of the as-machined sample. Such a modification in dislocation structures as well as increment in dislocation density corroborates the findings proposed by electrical resistivity measurement. The results demonstrated that electrical resistivity measurement provides a promising non-destructive approach for the early detection of fatigue damage in metallic materials.