Dynamic Delamination Crack Propagation in a Graphite/Epoxy Laminate

Ballistic impact tests of [90/0] 5 s T-300/934 graphite/epoxy laminates of beam-like dimension with embedded delamination cracks were conducted. High speed photography (16 000 frames/second) was used to record the impact response and subsequent crack propagation. From the photographic data, impact characteristics such as the contact duration and the dynamic response of the impact specimen were measured. In addition, the time of initiation of delamination propagation and measurements of the subsequent delamination length versus time were obtained. By changing the location of the embedded delamination in the specimens relative to the impact point, additional results were obtained on the variation of the threshold impact velocity necessary to cause crack propagation in the different specimen configurations. These data, together with the photographic results, suggest that the mode of crack propagation is dependent on the specimen geometry as well as the loading condition. The time dependent nature of the crack velocity and its variation with impact conditions was investigated. A finite element program was used to calculate the dynamic strain energy release rate before the onset of crack propagation. This strain energy release rate was used to gage the instability of the delamination crack during impact.