Acoustic emission behaviors and damage mechanisms of adhesively bonded single-lap composite joints with adhesive defects

Acoustic emission (AE) technology is widely applied for monitoring the damage of materials and structures. In this work, tensile tests were carried out to investigate the shear properties of adhesively bonded single-lap composite joints with adhesive defects. AE technology was used to evaluate the damage progress in real time. Besides, linear AE source location was also performed to study the damage initiation and propagation. Results show that the shear strength of adhesively bonded single-lap composite joints reduces as a result of the defects in the adhesive layers. Adhesion failure is found to be the dominant failure mode and most of the damage initiates and propagates at the edge of the adhesive layers and aggregates around the defects in the adhesive layer. Furthermore, the AE relative energy, amplitude distribution, cumulative hits and duration time are related to the damage process. The linear AE source location results are in consistent with the initiation and propagation of shear damage. For the adhesive joints with defects, AE signals with the amplitude from 60 to 80 dB increase at the evolution stage. It is suggested that the dynamic characteristics of AE signals can be effectively used to describe the damage mechanisms of adhesive bonded structure for composites.