Study On Evaluation Method Of Defect In Carbon Fibre Reinforced Plastic Plate Based On Magnetic Induction Tomography

Carbon Fiber Reinforced plastics(CFRP)is widely used in the aerospace field for its advantages of high specific strength,specific modulus,designable performance and easy overall shape.For example,the proportion of carbon fiber composite material in a foreign military aircraft is 25%-30%;and for foreign civil aircraft: airbus A350 XWB has exceeded 50%.In addition,it also has a huge market value in the automotive structure parts and sporting goods and other areas.However,a large number of CFRP materials are used as stressed structural components,which are prone to defects due to long-term impact of high strength,high load and large friction,thus leading to component or mechanical equipment failure or even a major accident.Therefore,the development and design of a new type of sensor for rapid detection of component damage areas is of great significance for preventing the fracture of key components of aerospace and preventing the occurrence of major malignant accidents.Based on the analysis of the eddy current detection principle of CFRP flat materials,a new type of MIT eddy current probe with two different placement methods was designed and developed based on Magnetic Induction Tomography(MIT).The 3D simulation model is established,and the detection performance of the two sensors is compared by means of numerical analysis,which proves the superiority of the unique design of the excitation coil and the central axis of the detection coil being perpendicular to each other.Moreover,the sensitivity of the sensor is further improved by optimizing the excitation frequency,coil turns,excitation current and lift off of the MIT probe structure parameters.Additionally,the sensitivity matrix of CFRP materials is calculated by designing a multi-channel MIT probe,which lays a foundation for image reconstruction of MIT inverse problemThe MIT detection system of CFRP was designed by modularization,and the excitation module,amplification module,phase sensitive detection and data acquisition module were completed by editing HF2 LI multifunctional phase-locked amplifier.Using Python programming controls the multiplexer 40-630-022 dual 16-channel multiplexing and real-time switching.Design and development of multi-channel MIT sensor and its automatic scanning to test the optimum detection frequency of MIT probe.And the stability and reliability of the detection system and the consistency of each channel of the probe are verified by repeated tests.Finally,the design of CFRP plate with different sizes of broken wire defects and layered defects to test the detection performance of the probe to obtain the defect signal induced voltage value.Furthermore,according to the sensitivity matrix and the defect induced voltage,the reconstruction algorithm is used to reconstruct the image of the CFRP plate.Linear inverse projection,Tikhonov regularization and Landweber algorithm were respectively analyzed theoretically.The influence of regularization factor and Lan coefficient were studied on image reconstruction results,and image reconstruction and evaluation were performed.The results show that MIT can realize the evaluation of 4mm×4mm× 0.5mm broken wire defects with a buried depth of 1.5mm in the CFRP plate,and the feasible detection of 10mm×10mm×0.5m layered defects with a buried depth of 1mm.