Numerical Investigation of The Influence of Adhesive Layer Thickness, Fillet Geometry And Reinforcement on The Creep Behavior of Single Lap Joint

Adhesive joints are widely used in the automotive, aerospace, and construction industries because they distribute loads uniformly, join dissimilar materials, and reduce structural weight. However, their long-term performance is strongly affected by creep, the time-dependent deformation of the adhesive layer under sustained loading, which can compromise joint integrity. This study presents a systematic numerical investigation of the combined effects of adhesive layer thickness, fillet geometry, and material reinforcement on the creep behavior of adhesively bonded single lap joints. Finite element simulations were performed in Abaqus using the Norton-Bailey power-law constitutive model, with validation against published results showing a maximum deviation below 7.5%. Four adhesive thicknesses (0.25-0.55 mm) were analyzed at both the elastic (t = 0.1 s) and creep-dominant (t = 4 h) stages. The results show that increasing adhesive thickness reduces peak shear stress and creep strain by approximately 15-25% and 20-30%, respectively, by promoting a more uniform load transfer along the overlap. The introduction of fillets at the overlap edges further mitigates stress concentration, yielding an additional 10-20% reduction in peak stress and strain. Carbon-fiber reinforcement of the adhesive produces the most pronounced improvement, decreasing peak creep strain by 44.68% for Epoxy A and 24.37% for Epoxy B. These findings provide design-level insights for enhancing the long-term durability of adhesively bonded joints through combined geometric and material optimization.