Influence of seawater condition on shear strength of CFRP single lap bonded joints with various fiber orientation

Abstract This study investigates the impact of seawater conditions on the single-lap joint properties of carbon fiber-reinforced vinyl ester resin (CFRP) with various fiber orientations (0°, 45°, and 90°). Specimens were tested under dry, wet, and dried conditions, with seawater immersion durations of 15 and 30 days, followed by a drying process. The failure modes, surface conditions, and chemical bonds were analyzed to understand the mechanism of influence of seawater on lap shear properties. The results show that fiber orientation significantly affects shear strength, with 0° specimens demonstrating the highest shear strength. In contrast, 45° and 90° orientations experienced substantial reductions. Seawater immersion decreased shear strength across all orientations. However, post-immersion drying restored and enhanced shear strength in 0° specimens, provided partial recovery in 45° specimens, and had limited effect on 90° specimens. Surface treatments improved bonding quality, and FTIR analysis indicated no significant permanent chemical changes due to seawater exposure. This research highlights the importance of fiber orientation in CFRP joint design for aerospace and marine applications. It suggests further exploration into long-term environmental effects and advanced surface treatments to enhance performance and durability.