Rotating Current Excitation with TMR sensor for Inspection of Magnetized Steel Fasteners

Rosell, A.; Michigan State University; USA

Su, Z.; Michigan State University; USA
Piero, D.; Michigan State University; USA
Rosell, A.; Michigan State University; USA
Udpa, L.; Michigan State University; USA
Udpa, S.; Michigan State University; USA

ID: ECNDT-0493-2018
Download: PDF
Session: Data Processing - ET
Room: J2
Date: 2018-06-11
Time: 13:50 - 14:10

Detection of fatigue cracks under fasteners poses one of the major challenges in the non-destructive evaluation (NDE) of aging aircraft fleet. Eddy-current (EC) coil with rotating excitation current together with giant magnetoresistive (GMR) sensors has recently emerged as a viable modality for rapid detection of defects in multilayered components. Defects might occur in different directions around the fastener and a rotating current excitation ensures sensitivity to defects of arbitrary orientation.
A major difficulty in defect detection is due to the fact that most cracks originate close to the rivet sites and are hence masked by the dominant signal from steels fasteners. A second issue due to the steel fasteners is that they can be magnetized and this further distorts the field measurements due to strong remanence fields and variability in permeability. In order to address these challenges we have developed an invariance transformation procedure that renders the signal insensitive to variability in relative permeability of rivet material, thereby increasing the detection probability of cracks under fastener head.
Results from simulated and experimental data will be presented to show the enhancement of EC-MR probe.