Development Of High-frequency Electromagnetic Eddy Current Detection System For Weakly Conductive Composite Materials

Nondestructive Testing(NDT)is an important branch of industrial field,which is mainly applied to detect defects or damage on the surface and inside of materials,parts and equipments,symbolizing the level of industrial development in a country.Compared with other NDT techniques,eddy current testing(ECT)method has the advantages of small size,non-contact,no need for coupling agent,no influence on the testing materials,etc.,which has been rapidly developed and widely used.In recent years,with the continuous emergence of new composite materials,the detection objects of electromagnetic eddy current detection technology are developing from the traditional metal conductive materials to the weak conductive composites,so the high-frequency electromagnetic eddy current detection technology has emerged.The present research and experiments show that the high frequency eddy current detection technology,combined with the advanced image processing algorithm,can be used to characterize the parameters of poorly conductive materials or even insulators to a certain extent,which indicates that it is feasible to use ECT technique to detect the damage of weak conductivity composites.A set of high-frequency electromagnetic eddy current testing system(hereinafter referred to as the high-frequency ECT system)was developed to realize the detection of damage forms such as crack,delamination and fiber fracture of weakly conductive polymer composites,and the detection results were visualized by the upper computer.The operating frequency is from 10 k Hz to 30 MHz,and the frequency can be adjusted flexibly according to the need.The system is with fully automated detection process,adopting embedded chip for control,which has high detection accuracy and the intuitive detection results.The specific research contents of this paper are as follows:1?According to the weak conductivity of the detection object,the functional parameter requirements of the high-frequency ECT system are summarized,and the overall design scheme of the system is proposed.The hardware circuit of the system is designed,including power management circuit,power amplifier circuit,phase-locked amplifier circuit,STM32 control circuit,sinusoidal signal generator circuit,AD acquisition and USB communication circuit.2?The software part of high-frequency eddy current detection system is developed,mainly including upper computer software based on Lab VIEW and lower computer software based on C.The function of the upper computer is to control the movement of the displacement platform and the acquisition of the lower computer,to save and display the detection results in real time.The lower computer is responsible for receiving the instructions from the upper computer and performing the corresponding operations.This paper gives the programming points and main program statements of each part of the software.3?The performance of high-frequency ECT system is verified by various scanning tests.The integrated system was used to detect the common damage of polymer composites,such as surface crack,internal delamination and fiber fracture,etc.The obtained detection images verified the expected performance of the system,and proved the feasibility of the high-frequency ECT system to detect the damage of weak conductive materials.The technical points,further improvement measures and development direction of the system are put forward.