Investigation of Artificial Cracks by Scanning SQUID Magnetic Microscope

We have investigated deep defects in structural Al-Ti alloy planar samples used in aeronautical application, by means of eddy current Non-Destructive Evaluation (NDE). The experimental system is a Scanning Magnetic Microscope (SMM) equipped with a high-critical temperature (HTc) dc Superconducting Quantum Interference Device (SQUID) magnetometer characterized by field sensitivity of 20 pT/(Hz)(1/2) and spatial resolution of about 50 mu m. We have detected cracks several millimeters below the surface, keeping relatively high spatial resolution. By mapping the magnetic field distribution, we can localize the sub-surface crack position. The experimental results confirm that this system could be used to detect defects with high resolution for the modeling of fatigue cracks in structures of aeronautical interest.