Scanning Induction Thermography for Bearing Ring Under AC-DC Composite Magnetization

Abstract

Induction thermography is a promising nondestructive testing technique with the advantages of high efficiency, lift-off tolerance, and defect imaging. To fulfill scanning detection and quantify the defect in bearing rings, this paper proposes scanning eddy current thermography under AC-DC composite magnetization. With DC magnetization, the defect will cause permeability disturbance in the bearing ring surface. Under high-frequency AC magnetization, disturbed permeability will generate a non-uniform thermal response captured by the infrared camera. To investigate the detection principle, a multi-physics coupling simulation model for permeability and thermal distribution in the scanning process is built, involving DC-AC composite magnetization, nonlinear ferromagnetic material, heat generation, heat conduction, and scanning movement. Then, a thermal data post-processing method for scanning imaging and crack quantification is proposed. Finally, the scanning induction thermography system for bearing rings is designed and developed. The experimental results show that the proposed scanning method can quantify bearing ring cracks with depths up to 2.0 mm.