This study investigates the effect of surface roughness on the shear strength of adhesive bonding joints with variations in material pairings, namely SUS304–Aluminum, SUS304–GFRP, and SUS304–SUS304. The tests were conducted using two surface roughness levels resulting from sanding: grit 40 (coarse) and grit 150 (fine). The results indicate that increased surface roughness significantly enhances the shear strength of the joints. Surfaces treated with grit 40 consistently yielded higher maximum shear strength compared to those treated with grit 150 across all material combinations. The highest shear strength was achieved in the SUS304–Aluminum joint with grit 40 at 37.436 MPa, followed by SUS304–GFRP at 36.456 MPa, and SUS304–SUS304 at 36.358 MPa. In contrast, for finer surfaces (grit 150), the highest shear strength was recorded in the SUS304–GFRP joint at 27.244 MPa. These findings indicate that surface roughness plays a significant role in enhancing the mechanical performance of adhesive bonding joints, where rougher surfaces improve material adhesion and shear load capacity. Among all tested specimens, the SUS304–Aluminum joint with grit 40 exhibited the highest shear performance, while the SUS304–GFRP joint with grit 150 demonstrated the best performance among the fine surface variations.
Keywords: Shear test, Adhesive bonding, Metal and non-metal joint