Research On Non-destructive Testing Of Polyimide Foam Multilayer Sandwich Structure

In order to solve the heat insulation problem of the outer panel of a satellite mounted solar wing,new material polyimide foam and its multi-layer sandwich structure have been used as the heat insulation material.The foam porosity of the multilayer sandwich structure and the adhesive interface bring great difficulties to the nondestructive testing of the structure.Aiming at the defect detection of polyimide foam multi-layer sandwich structure with multiple adhesive interfaces,a variety of nondestructive detection methods such as industrial CT,radiography,laser speckle interference,air-coupled ultrasound and infrared thermal imaging have been used.Through literature reading and investigation,a preliminary nondestructive testing scheme has been developed,prefabricated defect samples have been prepared,and experimental studies have been carried out.Of prefabricated defects sample testing results have showed that the radiography is suitable for detection of polyimide foam multi-layer sandwich structure,the minimum detectable debonding defect size for ?10mm in diameter,the thickness of 1mm;The minimum size of inclusion defect ?10mm in diameter,the thickness of 0.18 mm.The detection results of radiography are clear and intuitive,the size of defect image is accurate,the qualitative and positioning of defects is accurate,and the detection efficiency and sensitivity are high.Infrared thermal imaging to detect near surface defects effect is obvious,can detect more than 0.5mm thickness,diameter of not less than ?10mm inclusion defects.Laser speckle interference detection method of polyimide foam prefabricated defects sample diameter of less than ?20mm defect detection effect is not obvious.Air-coupled ultrasonic method is suitable for the determination of adhesive layer between polyimide foam and thin carbon fiber panel with thickness less than 30 mm.The reliability of industrial CT method is high,and the minimum thickness of inclusion defects can be detected is 0.18 mm.However,the working efficiency of industrial CT method is low,and the specification of detection parts is limited by the equipment capacity.Through summarizing and analyzing the experimental results,the following nondestructive testing scheme has been proposed for the multi-adhesive interface of 300mm×300mm×103mm polyimide foam sandwich structure:In combination with the manufacturing process of polyimide foam multi-layer sandwich structure,NDT was carried out for many times in the process: namely,the partsca-rbon fiber panel and structural plate were firstly NDT by laser speckle interferenceor la-ser holography.Then,the carbon fiber panel was bonded to the polyimide foam in acc-ordance with the structural bonding sequence,and the bonding surface was detected by infrared thermal imaging or air-coupled ultrasonic method.Finally,the structure plate w-as bonded with polyimide foam,and the interface was determined by X-ray photography or industrial CT.If the product size is not large,industrial CT method can be used to detect,otherwise,radiography method.