Pulsed Eddy Current Testing Technology Of Aluminum Honeycomb Structure Material Corrosion Defects

Aluminum honeycomb sandwich structure is a new type of aeronautical structure materials and an important part of the wing.Owing to its complexity and irregularity of the internal structure of the honeycomb core,defects detection of honeycomb structure with hidden corrosion is a difficult problem.Pulsed eddy current testing is a new non-destructive method and very sensitive to detection of corrosion defects of conductive material and is abundant in spectral information and convenient to use.This paper mainly studies the internal corrosion of aluminum honeycomb sandwich structure by using pulsed eddy current testing,including large area of corrosion defect and a small corrosion defect inside the honeycomb core.Major work is the design and implementation of the sensor and the algorithm to recognize the corrosion defects.By referring to the related literature and experiments,the TMR magnetic sensor is selected as the receiver of the probe and ferrite magnetic core as the probe’s magnetic core.For the large area of corrosion defect,traditional cylindrical probes are designed and manufactured.The experimental results show that cylindrical probes are capable of detecting the large area of corrosion defect.Probe’s parameters affect the detection sensitivity,and high sensitivity probe for shallow defects has different probe parameters from high sensitivity probe for deep defects.For small corrosion defects,detection sensitivity of cylindrical probe is very low.Rectangular probe,double angle probe and the ferrite frame u-shaped probe are designed.The experimental results show that u-shaped probe has the highest sensitivity for detecting aluminum honeycomb’s small corrosion.Optimization is done for u-shaped probe.The Probe’s structure is a u-shaped ferrite core with two coils wound on the plastic frame and placed at two ends of the u-shaped ferrite core respectively;a TMR magnetic sensor is placed in the middle of two ends of the u-shaped ferrite core.Using the optimized u-shaped probe to detect the aluminum honeycomb’s small corrosion defects,the probe can’t distinguish the depth of corrosion inside aluminum-skin aluminum honeycomb structure for depth 8 mm,10 mm and 12 mm,but the probe can distinguish the corrosion depth for depth 8 mm,10 mm and 12 mm for carbon-fiber-skin aluminum honeycomb structure.The paper analyzed the causeof this phenomenon.Scanning experiments are carried out in this paper.The experiments show that the greatest differential signal is obtained when TMR is perpendicular to the cellular wall and detection sensitivity is relevant to the scanning direction and scanning path.When scanning,the differential signal changes periodically.The algorithms are developed to recognize small corrosions based on the broken period.Eight channel arrayed TMR u-shaped probe is designed to detect small corrosions and time slice method is used to extract the characteristic value to make up characteristic matrix and implement C scan imaging.A summary is presented and some suggestions for future work are given.