Effect of carbon filler–modified epoxy adhesive on failure behavior of bonded single-lap joint: an experimental study combined with digital image correlation method

In this study, the effect of carbon filler–modified epoxy adhesive on the failure behavior of the single-lap joint (SLJ) was investigated through the experimental testing and digital image correlation (DIC) method. Carbon black (CB) and carbon fiber powder (CFP) were used as fillers to modify the adhesive. Carbon fillers were added individually into epoxy adhesive at the ratios of 0.5, 1, and 2.5 wt%. Pure and modified adhesive joints were tested under tensile load to determine the failure behavior of the joints. Moreover, DIC method was utilized to display the adhesive von Mises strain at the end of the bondline. Finally, SEM images were used to evaluate the fracture surfaces of the SLJs. As a result of the tensile tests, it was found that the CB- and CFP-modified epoxy adhesive increased the failure load and breaking displacement of SLJs. Among all the joints investigated in this study, SLJ bonded with adhesive containing 1 wt% CFP reached the highest failure load while the SLJ bonded with adhesive containing 2.5 wt% CB exhibited the highest toughness. DIC results and SEM observations revealed that the increase in the failure load and toughness of SLJs were associated with the increase in the ductility of the epoxy adhesive.