EFFECT OF REINFORCING TABS ON THE MODE I DELAMINATION TOUGHNESS OF STITCHED CFRPS

Stitching advanced carbon fibre composites in the through-thickness di rection enhances their interlaminar fracture toughness. To study this, composite specimens were fabricated from dry carbon fabric and resin using resin transfer molding (RTM) technique, and also from unidirecti onal prepreg tape. The stitching was performed with 2-ply (40 tex) Kev lar thread. It was observed during the mode I testing of RTM specimens using a double-cantilever-beam (DCB) test that the cantilever arms fa iled in bending, instead of crack propagating in a self-similar manner . Therefore, DCB specimens were reinforced with aluminium tabs along t he length of the specimens. To understand the effect of tabs on the mo de I toughness, prepreg specimens were tested with and without the tab s. The results indicated that the tabs altered the failure mechanism o f the stitching thread and the improvement in the mode I delamination toughness was underestimated. Specimens with varying stitch density we re studied. The steady-state toughness, G(IRs), of unstitched and stit ched specimens with and without tabs were compared. The addition of st itching was found to impart a 10-fold improvement in toughness. Experi mental results were also compared with theoretical predictions from a micromechanics-based model developed previously, and good agreement wa s found.