Study On Damage Detection Of CFRP Laminates Based On ET

Carbon fiber reinforced polymer(CFRP)is widely used in aerospace,national defense,automobile industry and other fields due to its high strength-mass ratio,chemical corrosion resistance and other excellent properties.CFRP laminates may be damaged during manufacturing and service due to process defects,fatigue,external damage and other factors.Hence,effective nondestructive testing methods for structural health are essential in its development.Electrical tomography(ET)is a kind of detection technology based on the electrical property of the tested object.As a portable,low-cost,radiation-free and non-destructive testing technology,ET has become one of the research focuses of damage detection.In this paper,the research on CFRP laminates based on ET method can be summarized as the following four parts.(1)Sensitivity matrix of electrical impedance tomography(EIT)is low in the center(far away from the electrode)and high in the four edges(near the electrodes)due to limited electrodes distribution.In addition,the inverse problem is ill-conditioned.Hence,regularization methods are often used to optimize the problem.However,threshold filtering(soft threshold,half threshold,etc.)used in common sparse image reconstruction algorithms may filter out the damage information in the central region.In order to solve this problem,an 8-neighborhood judgment method is proposed to improve the imaging effect of the central region.The effectiveness of the proposed method is verified by damage modeling simulation and actual experiments.(2)The commonly used EIT damage detection method evaluates the damage situation from the image perspective and fails to obtain some quantitative indexes so far.Combined with edge recognition,elliptic fitting,2D Gaussian fitting and 2 norm constraint,a damage assessment method which can be used to describe the damage location and area information is proposed.The effectiveness of the proposed method is verified by damage modeling simulation and actual experiments.(3)The sensitivity matrix of planar electrical tomography(PECT)sensor varies greatly between the electrode and the interval,resulting in a great difference in imaging effect between the electrode and the interval.To solve this problem,a rotatable fan-shaped electrode structure is proposed,in which the position between the electrode and the gap is interchanged by rotation,and the effect of sensitivity matrix homogenization is realized.The effectiveness of the proposed method is verified by damage modeling simulation.(4)A planar capacitance imaging(CI)sensor is designed.Compared with the traditional 2-electrodes CI sensor,the CI electrodes array reduces the variation of angle and relative distance between the sensor and CFRP laminates due to movement.In addition,the new electrodes structure has a larger relative length between the excitation and the measuring electrode,so that it has a better imaging effect.The effectiveness of the proposed method is verified by damage modeling simulation and actual experiments.