Detection and Characterization of Defects by the Electric Current Perturbation Method

The electric current perturbation (ECPl method of nondestructive evaluation is a powerful technique for detection and characterization of very small defects in nonferromagnetic material. It consists of establishing a current flow in the material to be inspected and then measuring current perturbations caused by nonconducting defects such as fatigue cracks. The current perturbation is sensed by a non-contacting magnetometer probe which detects the associated magnetic field perturbation. Recent findings from ECP investigations are reviewed in this paper. First, analytical modeling and experimental results show that single and multiple, closely spaced slots can be characterized from their unique ECP signatures; second, ECP inspection results from tiebolt holes in TF-33 gas turbine ·engine disks demonstrate the capability to characterize very small (0.305 mm long by 0.137 mm deep), tightly-closed, service-induced fatigue cracks; and third, preliminary results of an ECP experiment on a two layer fastener configuration show that radial slots in fastener holes can be detected in the second layer with the fastener installed