Electro-mechanic diagnostics of quenched AISI-4140 steel: An in-depth exploration using EMI/EMA techniques

The electromechanical impedance/admittance (EMI/EMA) method is a prominent technique in structural health monitoring. Its primary advantages include being non-destructive, straightforward in application, and cost-effective. This study examined the monitorability of quenching applications using the EMI/EMA method. EMI and EMA measurements were conducted on quenched AISI-4140 steel samples across frequency ranges of 30–80 kHz and 30 kHz–15 MHz. In this study, variations within frequency and amplitude ranges for parameters R min , R max , X , G min , G max , and B were assessed. Notably, in terms of frequency variation, the 30 kHz–80 kHz range showed a prominent variation of 1.26% for R min , R max , and X , while a 2.93% variation was observed in the G max measurements for the 30 kHz–15 MHz range. In terms of amplitude variations, the R min and G min measurements recorded the highest variations at 138.41% and 75.55% respectively. The RMSD values were greater than 1, indicating significant structural changes due to quenching, consistent with expectations in all frequency ranges. The CCDM values approached 1 for the lower frequency range (30–80 kHz), indicating significant structural changes due to quenching, consistent with expectations in this range.