Damage monitoring of conductive glass fiber/epoxy laminated composites under dynamic mixed-mode fracture loading

Abstract Damage monitoring of conductive glass fiber/epoxy laminated composites is performed by observing the electro-fracture response under dynamic mixed-mode fracture loading. A three-dimensional conductive network is generated in these composites by embedding carbon nanotubes (CNTs) in the matrix and reinforcing short carbon fibers (80 µm, 150 µm, and 350 µm) between the laminates. A modified split Hopkinson pressure bar setup is used to load the mixed-mode open notch flexure (MONF) specimens. A modified four-point probe technique coupled with a high-frequency data acquisition system is employed to capture the electrical response within process zone of the fracture specimens. A high speed video camera is used to capture the dynamic crack propagation. Due to the bending effect, a decreasing trend in resistance change is observed before the damage initiation in composites with no carbon fibers. However, short carbon fiber reinforced composites show a minimal change in resistance before the crack initiation due to less amount of CNTs in them and moreover short carbon fibers did not change their position during elastic deformation. After crack initiation, the rate of increase of resistance is almost five times higher in composites containing short carbon fibers of 80 µm than to those of 150 µm.