Mode II interlaminar fracture toughness of unidirectional interlayer hybrid FRP composites

This study focuses on developing hybrid pseudo-ductile FRP composites for externally bonded strengthening of reinforced concrete structures. 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 (𝐺𝐼𝐼𝑐) of the composites interface was measured through tensile testing on specimens 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 (𝐺𝐼𝐼) at the first fracture is lower than (𝐺𝐼𝐼𝑐). Both hybrid composites exhibited pseudo-ductile behavior with carbon layer fragmentation and dispersed delamination.