Differential ECT Probe Design and Investigation for Detection of Rolling Contact Fatigue Cracks With Different Orientations

Eddy current testing(ECT) is widely applied to detect surface defects on metallic materials. In ECT for cracks on complex curved surfaces, immunity to lift-off and the detection ability of the eddy current probe are critical challenges. In this study, we designed and developed a novel differential transformer ECT probe using AD698 signal conditioning to detect cracks with different orientations in rail treads. It adopts flexible printed circuit board (FPCB) technology for complex curved surfaces. The new ECT probe consists of four-square driver coils and two 8-shaped pick-up coils with antiserial connections that can sense opposite magnetic field changes in different directions. The proposed probe can solve the detection ability and lift-off problem of crack with different orientation on complex curved surfaces. The theoretical analysis which is based on transformer principles, is described in this paper. The detection ability of the new probe at different frequencies was evaluated by numerical simulation. Upon completion, the numerical simulations analyzed the effects of crack with different orientation and lift-off on the detection ability of the proposed probe. The experimental system was built to verify the detection ability of different crack with different orientations and immunity to lift-off by the proposed probe. The results of the simulation and experiment indicated that the proposed probe has a good ability to detect crack with different orientation whereas its performance decreases as crack orientation increasing. The proposed probe can also substantially suppress lift-off noise.