Investigating the structural integrity of single lap CFRP adhesive bonded joints

Single Lap Joints (SLJ), which are adhesively bonded, find extensive application in the lightweight composite structures, whose efficiency is largely determined by adhesive layer integrity and load transfer through the bonded interface. The mechanical behaviour of CFRP-CFRP (Carbon Fiber Reinforced Polymer) SLJs bonded with the help of an L-12/K6 epoxy adhesive in a 1:10 ratio is studied with systematic tensile tests and the material characterization in this case. To assess specimens of geometric influences independently, they were divided into two categories. In the former, the overlap length was changed to 15–40 mm while keeping the adhesive thickness of the adhesives constant at 0.4 mm. In the second experiment, the thickness of adhesives was between 0.2 and 1 mm when the overlap length was constant, 40 mm. Scanning Electron Microscope (SEM), Fourier Transform Infrared Spectroscopy (FTIR), X-Ray diffraction (XRD), and Surface Profile Measurement were used in the analysis of post-test fracture and surface characteristics. The experimental outcomes show that the thinness of adhesives enhances the strength of the joints because it allows the joint to transmit shear stress more effectively. Conversely, increase in adhesive layers pose undesirable redistribution of stress, which favors the shift of majorly cohesive brittle failure to mixed mode fracture and interfacial delamination. Furthermore, there was a systematic enhancement in load bearing capacity as the length of overlap increased and delamination has been found as the most common failure mode in joints that had higher strengths.