Experimental characterization of delamination in off-axis GFRP laminates during mode I loading

This work experimentally investigates the influence of the off-axis angle between the lamina orientation and the crack growth direction in mode I delamination of GFRP laminates having R-curve behaviour due to large scale bridging. Initial and steady-state fracture toughness are characterized for different configurations of two laminate designs using moment loaded DCB specimens. In layup design 1, the layers adjacent to the initial delamination are parallel and the off-axis angle is varied. For layup design 2, only the off-axis angle of layers adjacent on one side of the initial delamination is varied. Microscopy, fractography, and comparisons of R-curves are used as tools to classify the cracking behaviour. All off-axis configurations tested experienced crack migration from the initial crack plane. In layup design 1, a significant difference in initial fracture toughness are found as opposed to layup design 2 in which an insignificant difference in initial fracture toughness and steady-state fracture toughness, respectively, are found. The off-axis configurations of layup design 2 are associated with crack migration and intraply crack propagation. The transition from interlaminar to intraply crack propagation correlates with the location of off-axis fibers not supported by the initial delamination indicating a free edge effect of the DCB specimen.