Single‐Lap Joint Performance of Glass–Ramie Hybrid Epoxy Laminates: Effect of Adherend Surface Characteristics on Failure Mechanisms

ABSTRACT Hybrid glass–ramie fiber‐reinforced epoxy laminate offers a promising balance between mechanical performance and sustainability. This study investigates the tensile properties of glass fiber‐reinforced epoxy (GFRE), ramie fiber‐reinforced epoxy (RFRE), and hybrid glass‐ramie fiber‐reinforced epoxy (Hybrid G‐R) laminates and their single‐lap joint (SLJ) performance. Hybrid G–R laminates showed 147.8% and 196.2% higher tensile strength and Young's modulus compared to RFRE laminates, confirming the beneficial influence of hybridization on tensile behavior. Three SLJ configurations were tested using the same hybrid G–R laminate and epoxy adhesive: Glass‐adhesive–glass (G–G), Glass‐adhesive–ramie (G–R), and Ramie‐adhesive–ramie (R–R), differing only in the fiber surface in contact with the adhesive. The fiber surface in contact with the adhesive governed the SLJ performance. G–G and G–R SLJs showed comparable failure loads, while R–R SLJs achieved 35% higher apparent single‐lap shear strength due to stronger interfacial adhesion and progressive fiber failure at ramie fibers' surface. Failure analysis showed cohesive failure in G–G SLJs, mixed cohesive and fiber tear failure in G–R SLJs, and fiber‐dominated failure in R–R SLJs. Digital image correlation revealed asymmetric strain localization in G–R SLJs and a distinct crack‐jump mechanism in R–R SLJs, confirming that the adherend surface characteristics govern strain evolution and failure behavior in hybrid SLJs.