Split TMR-eddy current sensor monitoring of fatigue cracks in the inner layers of structures

Abstract

It is difficult to detect the inner fatigue cracks of the multi-layer structure on the aircraft in time, so there are serious safety risks. A split TMR (tunnel magneto resistance)-eddy current sensor is proposed in this work. With more turns of excitation coils to obtain a stronger initial magnetic field, the TMR chips array also increases the monitoring range. Fatigue test shows that the split TMR-eddy current sensor can monitor the expansion of inner layer fatigue cracks from 2 mm to 4 mm deep from the structural surface. For inner cracks of 2 mm depth, the sensor can distinguish cracks of 11 mm and 19 mm by using single frequency excitation mode, and the maximum monitoring sensitivity $S_C$ can reach 7.22 % and 5.42 %, respectively. The inner crack length can be quantified initially.