Effect of defects in the adhesive layer on strength of adhesively bonded single-lap composites joints

The tests on T700/TDE85 unidirectional laminates single-lap joints (SLJ) with defect and no defect in the adhesive layer under the uniaxial tensile loading were performed. Two different types of joints were designed and analyzed. According to the experimental results, failure modes of two kinds of joints were characterized and load-displacement curves were compared. It is appeared that interfacial failure is the major failure mode and the joint strength is slightly affected by defects with the small size in the adhesive layer. For investigating failure mechanism of joints, a finite element simulation was carried out to analyze the failure behavior and the peel/shear stress fields along the adhesive layer interface for the joints. It is found that the joint strength decreases with the decreasing length of defect location from the overlap end, and effect of length of defect location from the overlap end within 2.5 mm on the joint strength is more greatly. In addition, the joint strength decreases with the increasing of defect area, and area fraction of defect along the overlap zone within 4.4% has a little influence on the joint strength. The computational results are in good agreement with the experimental results.