For many applications of polymer matrix composites (PMCs) in real structures, it is difficult to avoid having parts bonded with similar or dissimilar materials. In general, bonded area has inferior mechanical properties than base materials to agreat extent because of the existence of interfacial or transitional region which show quite different gradient in chemical and microstructural aspects. Therefore, bonded parts can be more critical than base structures to determine the overall integrityof mechanical structures[l]. There are two possible methods for joining of PMCs or fiber reinforced plastics(FRPs), the mechanical as well as the adhesive bonding. The latter has been widely adopted since the joints can extend fatigue life, reduce totalweight of structures, and homogeneously transfer stresses. Various non-destructive testing methods such as ultrasonics, acoustic emission(AE), acousto-ultrasonics(AU), radiographic testing have been used for the evaluation of bonded region. Especially AUmethod can provide detailed information about bonded region by analyzing the acquired signals which pass through defects, failures or damages of structures[2].
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