Numerical Analysis on Optimal Adhesive Thickness in CFRP Single-Lap Joints Considering Material Properties

Accurately evaluating the strength of adhesively bonded joints is essential for ensuring structural reliability, but size-dependent effects remain a challenge in consistent strength assessment. This study performs finite element simulations of Single Lap Shear (SLS) tests, focusing on the local stress state at fracture initiation. The analysis considers unidirectional and quasi-isotropic carbon fiber reinforced plastic (CFRP) adherends combined with three adhesives: polyphenylene sulfide (PPS), polyether ether ketone (PEEK), and epoxy. Adhesive thicknesses ranging from 0.1 mm to 0.5 mm are evaluated. The results indicate that the optimal thickness ranges between 0.1-0.3 mm to maximize joint strength, while excessively thin or thick layers reduce performance. These findings align with experimental trends and support the development of precise design guidelines for polymer-based joints in structural applications.