Research On Defect Dection Technology Of Radar Absorbing Coating Based On Sherography

The radar absorbing coating is the core structure of modern fighter to achieve stealth function.However,because of the heterogeneous structural characteristics of the absorbing coating material and the aircraft base material,it is easily damaged during work and is easy to produce debonds during spraying process.These defects have a great impact on aircraft safety.Therefore,the research on the detection technology of radar absorbing coating material not only has important significance for the its application,but also has more practical significance for promoting the development of stealth technology in China.The debonds defects are highly concealed so that there are many difficulties in detection of the debonds defects which may have enormous harm to the stealth craft.However,whether it is infrared thermal or ultrasonic method,they all have obvious limitations.Laser shear speckle interferometry,named Sherography,is a non-contact,large-area non-destructive technique in recent years.When the coating is loaded by heat,the defects between the coatings and the substrate will cause abnormal stress distribution of the coating's surface.This program will collect speckle interference patterns before and after loading,and then make subtractions.The abnormal fringe images reflect the surface or interior defects of the costings.In order to realize the visual detection of radar absorbing coating defects based on laser shear speckle interference,the main work of this paper are as follows:1.First of all,this paper conducts in-depth theoretical research on defect detection based on laser shear speckle technology and establishes a mathematical model for debonds detection.Because the debonds are simulated by waxing between the coating and the substrate,thermal stressing is used in this research.What's more,thermal stress simulation analysis of the layered plate is conducted on finite element.2.This program contrasts and analyze the common shear elements,and consider practical applications and costs to set up an improved Michelson laser shear speckle interference defect detection platform.Besides,a software platform which drive the detection system and display the results of inspection is designed in this paper.Last,we test the platform multiple times and establish a reasonable defect detection plan.3.Lastly,we conduct experiments on the radar-absorbing coating materials with the platform to achieve visual inspection of coating debonds defects.The speckle interference intensity difference images before and after deformation of the measured object are obtained.This paper analyze the source and characteristics of the noise,propose a four-step phase-shift algorithm based on adaptive filtering to extract phase information and a windowing Fourier smoothing algorithm based on improved threshold proposed to remove the noise signals.Because of the non-uniformity of material spraying,a regional phase unwrapping method based on fringe estimation and phase map segmentation is used to process the phase image.Finally,the results of the detection of coating defects by three inspection methods are compared to be analyzed.The result proves that the Sherography is effective and can realize high-quality rapid visual inspection of debonds defects.