Determination of dynamic delamination toughness of a graphite‐fiber/epoxy composite using Hopkinson pressure bar

Modified dynamic three‐point‐bending and compact shearing test configurations based on Hopkinson pressure bar (HPB) and crack detection gage (CDG) (Vishay Intertechnology, Inc) were used for the determination of the dynamic mode I and mode II delamination‐initiation toughness of a unidirectional graphite‐fiber/epoxy composite made of P7051S‐20Q‐1000 prepregs (Toray Composites America). The transient loading history was recorded precisely by the HPB installed with a high‐resolution digital oscilloscope, and the crack initiation and delay time were captured using the CDG. By means of dynamic finite‐element analysis (FEA) of the impact processes with the loading history and crack initiation time as input, the critical dynamic stress intensity factors (DSIFs) (K IDC /K IIDC ) were extracted from numerical results of the crack opening displacements (CODs). Results show that under the present transient loadings, the K IDC value is about 80–90% of the static one, while the K IIDC value is nearly unchanged. Dynamic failure mechanisms of the composite specimens were evaluated by fractography using a scanning electron microscope (SEM). POLYM. COMPOS., 26:165–180, 2005. © 2005 Society of Plastics Engineers