Research On The Performance Of A New Differential Excitation Flexible Fractal Eddy Current Sensor For Crack Detection

Complex shaped metal components are widely used in the fields of aerospace,national defense,marine and shipbuilding.To ensure that the metal components can be used properly,the all parameters of the metal components must meet the production and use requirements to ensure the safety of equipment operation.However,the operation of equipment in high temperature,high pressure and other harsh environments may cause cracks and other defects in metal components,thereby reducing the quality and safety of equipment operation,so Non-destructive Testing of metal components is essential.Compared with other non-destructive testing,eddy current testing has the advantages of non-contact,high efficiency,low cost and convenient operation,and is widely used in the assessment of structural integrity of metal components.To solve this problem,we design a new type of differential excitation flexible fractal eddy current sensor based on fractal geometry theory and investigate the performance of the sensor in detecting defects on the surface and subsurface of aluminum test blocks.The specific research work is as follows:(1)Firstly,a fractal curve is proposed and a new type of differential excitation flexible fractal eddy current sensor is designed based on this curve,which is a singletum sensor,noted as K0,M6-K1,M6-K2,M6-K3,M10-K1,M10-K2,respectively.The working principle and design ideas of this type of sensor are systematically introduced.The crack detection performance of six single-turn eddy current sensors is compared by experimentally scanning cracks of different geometries.When scanning 0 °cracks,the transimpedance peaks of the sensors were similar at excitation frequencies of 100 k Hz,200 k Hz,and 500 k Hz,and the transimpedance peaks of the sensors varied greatly when the excitation frequency was increased to 1000 k Hz,so it was difficult to select the optimal sensor for detecting 0 ° cracks;when detecting 90 ° cracks,the transimpedance peaks of the M6-K3 sensors at each excitation frequency is the largest.Therefore,the M6-K3 sensor has the best crack recognition capability.(2)To further investigate the performance of the M6-K3 sensor,scanning tests were performed by cracking cracks of different lengths,depths,widths,angles,etc,and the performance of the sensor under different test conditions was investigated.From the test results,it can be obtained that: when the crack angle is 0 ° ～ 90 °,for a3 mm crack,the detection performance of the sensor on the crack decreases with the increase of the crack angle;for 5 and 10 mm cracks,the detection performance of the sensor on the crack increases with the increase of the crack angle;the detection performance of the sensor on the crack increases with the increase of the crack width;the detection performance of the sensor on the crack increases with the increase of the crack width;the detection performance of the sensor on the crack increases with the increase of the crack angle;the detection performance of the sensor on the crack increases with the increase of the crack angle.The detection performance of the crack increases with the increase of the excitation frequency;the detection performance of the crack increases with the increase of the crack length and then decreases;the detection performance of the crack decreases with the increase of the lifting distance.(3)Considering the waste of space caused by the layout of single-turn sensor detection coil and the influence of the increase of coil turns on the performance of the sensor,a multi-turn flexible planar eddy current sensor is designed,which is marked as multi-turn K0,M6-K3 and M10-K2 respectively.The design of the multi-turn sensor is based on the single-turn sensor,the number of turns of the excitation coil is kept unchanged,the number of turns of the detection coil is increased until the processing limit,and finally the multi-turn flexible planar eddy current sensor is formed.In order to study the performance of the multi-turn sensor,Through the analysis and comparison of the results of the tests on the surface cracks of aluminum test blocks and the internal cracks of different thicknesses with single and multi-turn K0,M6-K3 and M10-K2 sensors under different lift-off and frequencies,it is concluded that the crack detection performance of multi-turn K0,M6-K3 and M10-K2 sensors is higher than that of single-turn K0,M10-K2 eddy current sensor.