Estimation of interfacial toughness using bilayer fiber bundle compact tension (BFBCT) specimens

This work aims at characterizing the interfacial toughness based on the mode I interlayer fracture toughness of bilayer fiber bundle compact tension (BFBCT) specimens. Extensive fiber/matrix interfacial deboning was found along the crack propagation path in mode I delamination test of BFBCT specimens. The apparent GIc values could distinguish interfacial toughness properties of different carbon and aramid fiber/matrix systems. The transverse fiber bundle tension (TFBT) test for evaluating interfacial bonding strength was also performed as a comparison. It was found that the interface between T800H carbon fiber and epoxy was both the strongest and the toughest among all tested carbon fiber/epoxy interfaces. Compared with carbon fibers, aramid fibers possessed a higher interfacial toughness but a lower interfacial strength. The mode I delamination test of BFBCT specimens is a simple and reliable method for evaluating interfacial toughness in composites. BFBCT test as well as TFBT test can be used to comprehensively characterize the strength and toughness properties for fiber/matrix interface based on fiber bundle specimens.