REAL-TIME VISUALIZATION OF FIBER/MATRIX INTERFACIAL DEBONDING BEHAVIOR

The rate effect of fiber-matrix interfacial debonding behavior of SC-15 epoxy and various fiber reinforcements was studied via in-situ visualization of the debonding event. Special focus has been placed on the dynamic transverse debonding of single fiber reinforced polymer composites. In this study, the debonding force history, debonding initiation, debonding crack velocity, and crack geometry were characterized using a quasi-static load frame and a modified tension Kolsky bar at loading velocities of 0.25 mm/s and 2.5 m/s. Cruciform-shaped specimens were used for interfacial transverse debonding between SC-15 epoxy matrix and various fiber reinforcements including S-2 glass, Kevlar® KM2, and tungsten fiber materials. The load history and high-speed images of the debonding event were simultaneously recorded. A major increase was observed for the average peak debonding force and a minor increase was observed for the average crack velocity with increasing loading velocity. The crack geometry of the cruciform specimens under both loading velocities was also tracked. Scanning electron microscopy of the recovered specimens revealed the debonding direction along the fiber-matrix interface through angled patterns on the failure surface.

The dynamic shear debonding of single fiber reinforced plastic composites were also studied via the real-time visualization with the fiber pull-out method. The interfacial shear debonding was studied between SC-15 epoxy and fiber reinforcements including S-2 glass, tungsten, steel, and carbon composite Z-pin fiber materials at 2.5 m/s and 5.0 m/s. Both S-2 glass fiber and Z-pin experienced catastrophic interfacial debonding whereas tungsten and steel wire experienced both catastrophic debonding and stick-slip behavior. Scanning electron microscope imaging of recovered epoxy beads revealed a snap-back behavior around the meniscus region of the bead for S-2 glass, tungsten, and steel fiber materials at 5.0 m/s whereas those at 2.5 m/s exhibited no snap-back behavior.