Effect of Process Parameters on the Geometry of Composite Parts Reinforced by Through-the-Thickness Tufting

Inserting discrete through-the-thickness reinforcing elements such as fibrous tufts into a composite laminate may increase dramatically its damage tolerance and impact resistance. The three-dimensional fibre architecture generated locally by such elements (sometimes referred to as micro-fasteners) has been demonstrated to slow down or arrest altogether delamination crack growth. Where a closed, matched tool is used for infusion and cure, the insertion of tufts may result in a local increase in fibre volume fraction. On the other hand, when a flexible sealant bag or film is used, the extra fibrous yarn may cause an increase of the laminate thickness, with potential alteration of the component geometry. The latter effect may impact upon the component performance, especially if aerodynamic surfaces are involved, and therefore needs systematic quantification. This paper quantifies the alteration in thickness of a flat laminate made with non-crimp carbon fabric and reinforced with carbon tufts using a range of material and manufacturing variables. A design of experiments approach is applied and a 3D laser scanner used to gather reliable data to identify those parameters most likely to influence the change of geometry (including yarn weight, tuft areal density and tuft angle). A case study is presented to relate the experimental findings to the case of a 900 mm long, double curvature carbon fibre tufted T-stringer made with a 3D woven pi-section.