Research on defect detection in non-ferromagnetic materials based on an induced magnetic field testing method

Area of Science:

• Materials Science
• Physics
• Engineering

Background:

• Conventional eddy current testing relies on excitation coils, leading to bulky and less accurate detection apparatus.
• There is a need for advanced non-destructive testing (NDT) methods with improved sensitivity and portability.

Purpose of the Study:

• To introduce a novel defect detection method utilizing induced magnetic field measurements.
• To develop a compact and highly accurate sensor system for identifying microdefects.

Main Methods:

• Employing a millimeter-scale permanent magnet as the excitation source.
• Utilizing a high-precision tunnel magnetoresistance sensor to detect magnetic field perturbations.
• Conducting vector analysis through experiments and numerical simulations.
• Interpreting signal characteristics using an equivalent parallel circuit model.

Main Results:

• Successfully detected microdefects as small as 10 μm.
• Demonstrated that smaller defects increase detection difficulty, while higher motion velocity enhances sensitivity but reduces detection depth.
• Identified an optimal lift-off distance of 0.2 mm for detection performance.

Conclusions:

• The proposed method offers a coil-free, compact, and high-precision alternative to traditional eddy current testing.
• The sensor system shows significant potential for practical NDT applications, including fatigue crack detection in high-manganese steel for railway tracks.