DYNAMIC MODE-I CRACK-PROPAGATION IN A CARBON EPOXY COMPOSITE/

A modified DCB specimen has been used to study the dynamic Mode-I dela mination fracture toughness of an AS4/3501-6 carbon/epoxy composite at high crack-propagation speeds. A strip of FM-73 adhesive film was pla ced at the tip of a pre-crack created during laminate lay-up. The adhe sive strip substantially increased the crack-initiation toughness so t hat after initiation an unstable crack-propagation was produced and hi gh crack-propagation speeds were achieved. Specimens were loaded at a constant displacement rate of 0.1 mm s(-1) on an MTS machine. Crack ex tension was monitored by means of a conductive circuit placed along th e path of the propagating crack. Continuous records were obtained for the load, deflection and crack extension. The strain-energy release ra te was calculated by using plate finite elements based on the crack-pr opagation data. It was found that the critical dynamic strain-energy r elease rate for crack speeds up to 200 m s(-1) is a constant and is eq ual to the critical static strain-energy release rate. (C) 1998 Publis hed by Elsevier Science Ltd. All rights reserved.