On the effect of stitching on mode I delamination toughness of laminated composites

Two simple micromechanics-based models have been proposed to study the effect of through-thickness reinforcement (stitching) in improving the delamination crack growth resistance double-cantilever-beam specimens. In the first model, it is assumed that the stitches are not interconnected, as in most cases the top and the bottom surfaces of the stitched laminates are ground off to remove surfaces in-plane waviness caused by the stitching loops. In the second model, the effect of interconnected stitches is studied. These models are then used to examine the effects of stitch density, matrix/stitch-thread interfacial shear stress, stitch-thread diameter, volume fraction of stitches, bending stiffness of the beam and critical stress intensity factor of the composite on Mode I delamination toughness.