Mode II interlaminar fracture toughness of unidirectional interlayer hybrid FRP composites

This study focuses on the characterization of hybrid pseudo-ductile FRP composites for externally bonded strengthening of reinforced concrete structures, which were initially developed in a previous work. Three types of dry unidirectional fabrics were used to create two interlayer hybrid composites via hand lay-up: (i) glass with ultra-high modulus carbon and (ii) high strength carbon with ultra-high modulus carbon. The mode II interlaminar fracture toughness (G IIc ) of the composites interface was measured through tensile testing on coupons with a single cut in the central carbon layer. It was confirmed that catastrophic delamination can be prevented if the mode II energy release rate (G II ) at the first fracture is lower than G IIc. Both hybrid composites exhibited pseudo-ductile behaviour with carbon layer fragmentation and dispersed delamination. • Hybrid carbon-carbon and glass-carbon FRP composites. • Pseudo-ductility in hybrid FRP composites. • Fragmentation and stable delamination of hybrid FRP composites. • Mode II interlaminar fracture toughness of the composites interface. • Mode II interlaminar fracture toughness assessed by testing.