ON THE EFFECTS OF STITCHING IN CFRPS - I - MODE-I DELAMINATION TOUGHNESS

Stitching advanced carbon-fibre composites in the thought-thickness di rection enhances the interlaminar fracture toughness. The mode I delam ination roughness of a carbon/epoxy composite, both unstitched and sti tched, was experimentally determined by using double-cantilever beam s pecimens. Specimens with varying stitch density, thread diameter and t hread type were studied. The steady-state toughnesses, G(IRs) Of unsti tched and stitched specimens have been compared. The addition of stitc hing was found to create an improvement in toughness of up to 15 times . The energy-dissipating crack propagation processes were determined a nd critical parameters identified. In addition, experimental results w ere compared with theoretical predictions from a micromechanics-based model developed previously and good agreement was found. (C) 1998 Else vier Science Ltd. All rights reserved.