An investigation on the mechanical behavior of mixed adhesively bonded composite joints subjected to transverse pre-impact following by axial post-tensile

In this study, mixed adhesive joints were formed to create a more homogeneous stress distribution in order to increase the failure load that the joints could bear. Single-lap joints (SLJs) made of glass fiber-reinforced plastic (GFRP) composites were formed using a rigid adhesive (Araldite AV138) in the middle and a more flexible adhesive (3 M DP8005) at the ends of the joint. Rigid and flexible adhesives were applied to the surface with lf/lr = 1 and lf/lr = 0.5 bond-length ratio (lf is bond length for the flexible adhesive and lr is bond length for the rigid adhesive). Mono adhesive joints were also created using the same adhesives. Tensile tests at 1 mm/min were carried out without applying pre-impact to some joints and applying 2.5, 3.5, 7.5, and 10 J transverse impacts to other joints to reveal how joint strength changes with the potential impacts to which adhesive joints might be exposed. Mixed adhesive joints bore more load under impact and non-impact conditions compared to mono adhesive joints. The impacts applied in these tests increased the load-bearing capacity of mono DP8005 adhesive joints. The largest decrease of strength after impact was observed for the mixed adhesive joints with lf/lr = 0.5 bond-length ratio.