This paper develops a high-sensitivity flexible eddy current array (HS-FECA) sensor for crack monitoring of welded structures under varying environment. Firstly, effects of stress, temperature and crack on output signals of the traditional flexible eddy current array (FECA) sensor were investigated by experiments that show both stress and temperature have great influences on the crack monitoring performance of the sensor. A 3-D finite element model was established using Comsol AC/DC module to analyze the perturbation effects of crack on eddy currents and output signals of the sensor, which showed perturbation effect of cracks on eddy currents is reduced by the current loop when crack propagates. Then, the HS-FECA sensor was proposed to boost the sensitivity to cracks. Simulation results show that perturbation effect of cracks on eddy currents excited by the HS-FECA sensor gradually grows stronger when the crack propagates, resulting in much higher sensitivity to cracks. Experimental result further shows that the sensitivity of the new sensor is at least 19 times that of the original one. In addition, both stress and temperature variations have little effect on signals of the new sensor.

This paper investigates effects of temperature variation on output signal of rosette eddy current array (RECA) sensor and proposes a new RECA sensor with temperature compensation capability for quantitative monitoring crack of bolt-jointed structures. A temperature simulation experiment shows that temperature variation has a great influence on output signal AR of RECA sensor as crack does and even results in false alarm when environment temperature changes. Temperature-compensated RECA (TC-RECA) sensor using the new output signal ΔC considering impacts of conductivity and lift-off is developed to eliminate impacts of temperature variation on monitoring process. Then, the relation between crack length and output signal ΔC is obtained by an online monitoring experiment, which shows TC-RECA sensor can quantitatively monitor crack with an accuracy of 1 mm. Then, a temperature simulation experiment is performed to verify the sensor’s ability to eliminate effects of temperature variation on monitoring process. Results shows that output signal ΔC just changes within about 0.5% when temperature changes from −20 °C to 70 °C, which has no effects on monitoring process. Finally, a crack monitoring experimental of a bolt-jointed structure under temperature disturbance is performed to verify the sensor’s abilities of quantitative monitoring crack of bolt-jointed structures and temperature compensation. It can be concluded that TC-RECA sensor has the ability to eliminate effects of temperature variation and can quantitatively monitor crack of bolt-jointed structures with an accuracy of 1 mm.

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