ONSET OF KISSING BOND FORMATION FOR VARYING LEVELS OF BONDLINE CONTAMINATION IN CFRP
Cantrell, Daniel Riley
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Carbon Fiber Reinforced Polymer or CFRP is an important and widely used material in the aerospace industry. CFRP utilizes adhesive bonding as the primary joining method and may suffer from a defect known as a kissing bond. This occurs when there is very close contact between the CFRP substrate and the adhesive yet very low bond strength. This makes kissing bonds very difficult to detect with typical non-destructive inspection (NDI) since they lack a substantial discontinuity. Previous work at Georgia Tech Manufacturing Institute has developed a reliable method of creating intentional kissing bonds by applying a controlled amount of contaminant to the CFRP surface before adhesive bonding. Data produced by this work has been divide into two categories, “pristine” where there is no contaminant applied and the bond exhibits normal behavior with high strength and “contaminated” where a large amount of the contaminant is applied creating a kissing bond and resulting in very low strength. Surface cleanliness is verified using water contact angle measurements, which result in very low contact angles for pristine surfaces and high contact angles for contaminated surfaces. This work focused on investigating the intermediate area between these two extremes termed “intermediate contamination” in order to: 1) Determine the relationship between contaminant concentration and contact angle 2) Produce lap joint specimens with intermediate contamination 3) Produce double cantilever beam specimens with intermediate contamination The potential presence of kissing bonds drive strict regulations for the usage of CFRP in the aerospace industry and developing methods of detecting kissing bonds are a key step in improving safety, reducing maintenance cost and increasing reliability of its use. The goal is to provide researchers with a better understanding of kissing bond formation and methodologies to produce CFRP bonds with intermediate contamination which will aid in the development of non-destructive inspection for kissing bonds in CFRP.