Traction law for inclined through-thickness reinforcement using a geometrical approach

Stitching of laminated composites is a proven way to improve damage tolerance and increase interlaminar fracture toughness. However, the size and shape of various composite parts manufactured across many industries has limited possible applications of stitching. Innovative one-sided stitching techniques incorporating inclined stitches have emerged to overcome these limitations. Models for determining traction laws for individual stitches including inclined stitches have progress over the years but with limitations. A model for analysing a stitch, pin or other through-thickness reinforcement in a composite laminate has been developed and validated with finite element analysis (FEA). This model is formulated based on treating the stitch as a rope supported by a plastic foundation, with pull-out resisted by frictional stresses. A new approach was taken to determine the displacement by integrating the function describing the shape of the stitch. The model accurately predicts the traction law of a stitch and is most accurate for cases where μ and θ0 are small. This model can be incorporated with FEA to simulate the delamination of laminates. This reduces the need for expensive experimental testing and allows for the most effective stitching parameters to be determined, resulting in optimal design.