Weak bond effects in adhesively bonded joints between the dissimilar adherends

Adhesively bonded joints provide uniform stress distributions for the width in the bonded region, which is preferred for lightweight assemblages in aircraft structures, but the bonded region is hidden between adherends and suffers due to the existence of weak bonds. Adhesively bonded joints between dissimilar adherends are susceptible to weak bonds due to large differences in the properties and behaviour of adherends. Weak bonds present at the interfaces due to improper curing of adhesive, may go undetected and affect the bond strength. In this paper, an attempt has been made to characterize weak bond effects in adhesive bonded joints between dissimilar adherends. Adhesively bonded single lap joint specimens have been fabricated with CFRP and aluminium using Araldite-2015 adhesive with varied areas of weak bond. PTFE (polytetrafluoroethylene) films used to introduce weak bonds in the bonded region. X-ray radiography and ultrasonic tests have been performed on specimens to verify the presence of weak bond areas. Uniaxial tensile tests have been conducted on specimens to evaluate the mechanical response of adhesive joints in the presence of weak bonds and to obtain failure loads and corresponding failure patterns. Finite element analysis has been carried out to evaluate variations of peel and shear stresses along the bond length. From the studies, it is found that failure occurs at the interface where weak bonds are present irrespective of dimensions of weak bonds and the corresponding failure load decreases with increase in the weak bond area resulting in interface failure