Non-destructive characterization of bondlines in composite adhesive joints

Abstract Aerospace structures use polymeric composite materials extensively. These composite materials are normally bonded together by adhesives to form structural parts. The existence of any kind of defects or discontinuities in the bonds is completely undesirable for such applications. Ultrasonic imaging (UI) is a widely used technique for non-destructive evaluation (NDE) and can be adopted to evaluate the integrity of such adhesively-bonded joints. However, characterization of adhesive bonds in composite materials using UI has deficiencies due to problems such as high acoustic attenuation and high signal-to-noise ratio. These problems can be attributed to the inhomogeneity in composite structures. The present study addresses the problems of detection of disbonds and porosity in adhesively bonded carbon fiber reinforced composite panels. Five sets of adhesively-joined carbon/epoxy composites with different adherend surface preparations were fabricated and subjected to UI. The panels contained known defects in the bondline of the samples. UI results are interpreted to identify various existing defects such as voids, cracks and disbonds in the joints. Attenuation coefficient values for all types of composites are utilized to ascertain the validity of the image analysis. Keywords: COMPOSITE ADHESIVE JOINTSULTRASONIC IMAGINGNON-DESTRUCTIVE EVALUATIONPOROSITYATTENUATION