An experimental study on mode I and II fracture toughness of laminates stitched with a one-sided stitching technique

Double cantilever beam (DCB) and end notch flexure (ENF) tests were conducted on laminates stitched using the ITA one-sided technique with two different diameter threads. The DCB results showed the larger diameter produced higher fracture toughness, however, due to the higher stitch loads and variable stitch spacing some rows would break in pairs. This is not preferable for stable crack growth and is a consideration that needs to be taken into account when designing stitch patterns. The ENF tests showed no clear difference in the initial fracture toughness due to the different diameters. At the maximum crack length the larger diameter led to a higher toughness due to the higher residual load and greater saturation length. The cases for with the nap had higher initial fracture toughness, however, the lower residual loads result in lower fracture toughness at higher crack lengths.