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

The fibre geometry resulting from the addition of through-thickness fi bres in the form of stitching generates considerable improvement in th e mode I delamination toughness of laminated carbon fibre composites. However, interlaminar shear, caused either by direct loading or from e ccentricities in the structural load path resulting in out-of-plane lo ading, is a critical loading condition in many composite structures, T his paper investigates the effect of stitching on the mode II delamina tion toughness. The mode II delamination toughness of a carbon/epoxy c omposite, both unstitched and stitched, was experimentally determined using an end-notched flexure (ENF) specimen. Specimens with varying st itch density, thread diameter and thread type were studied. The steady -state toughness, G(IIRs), of unstitched and stitched specimens were c ompared. The addition of stitching was found to create an improvement in toughness of up to 4 times. In addition, experimental results were compared with theoretical predictions from a micromechanics-based mode l developed previously. (C) 1998 Elsevier Science Ltd. All rights rese rved.