Non-destructive evaluation of composite adhesive kissing bond

Adhesive bonded joints have been increasingly employed in aerospace, automotive, and other mechanical systems due to the advantages of uniform stress distribution, less stress concentration, light in weight, etc. However, the early damage stage of the adhesive bond joints, which are usually named as kissing bond, can significantly impact the structural integrity and safety. Kissing bond is difficult to detect and identify using current non-destructive evaluation (NDE) techniques since there is no clearly gap or interface between the bond area. Attempts using advanced ultrasonic methods have reached limited success, but more reliable methods need to be developed before adhesive joints can be more widely applied to the engineering field. This paper focuses on the development of detection method using digital image correlation (DIC) technique. Three types of adhesive kissing bond joint samples were fabricated using different contamination recipe to simulate the kissing bonds. The performance of the fabricated joint samples were tested using uniaxial hydraulic test frame and the detection capability of DIC system was investigated. The noncontact strain field measurement method using DIC can indicate the existence of kissing bonds with limited load. The results of DIC measurement is encouraging and can be further used for the NDE estimation of mechanical properties of the kissing bond.