Experimental Investigation on the Inspection of Cracks on Threaded Surfaces Using Electromagnetic Thermography

As an important connection type, threaded connections are very easily damaged by cracks on the threaded surfaces during the production and service period, which would lead to mechanical failure. The complicated geometry of threaded connections brings great challenges to conventional non-destructive testing (NDT) methods. Thus, it is important to develop an advanced and suitable NDT technology to detect cracks on threaded surfaces. This study investigates the applicability of electromagnetic thermography (ET) for crack inspection. The inspection principle was examined based on electromagnetic and thermal conduction laws. Experiments were conducted on four bolts with cracks on their threaded surfaces using ET technology. The effectiveness of ET was verified through the analysis of thermograms and temperature responses. In addition, we also study the influence of several key parameters, including excitation coil orientation, excitation coil location, the amplitude of excitation current, and crack size, on the detection results. The findings indicate that ET offers an efficient and practical method for inspecting cracks on threaded surfaces.