Influences of ply waviness and discontinuity on automated fibre placement manufactured grid stiffeners

•Behavior of grid stiffener was studied in view of ply waviness and discontinuous ply.•Feasibility of grid manufactured by automated fibre placement was validated.•Same performance of grid stiffener is achieved by discontinuous ply as continuous layup.•Pseudo-ductility is introduced in grid stiffener by discontinuous ply under bending. Advanced grid structures can realise significant weight savings, compared to conventional stringer stiffened structures. Overlaps of the transverse tows create fibre drop-off around the intersection region. As a result, this creates a potential weak point of whole advanced grid stiffened structures. Localised buckling at the intersection region is imminent under compressive loading. In order to overcome this shortfall, an automated fibre placement based method to improve the microstructure of grid stiffener is proposed in this paper. In this method, discontinuous plies are introduced into rib to remove excessive material at the intersection. The influences of fibre waviness and discontinuous plies on the microstructure, mechanical performance of grid stiffener are investigated using experimental and finite element methods. Results show that structural efficiency of grid stiffener can be improved significantly with appropriate ratio of discontinuous plies in the intersection of grid stiffener. Corresponding finite element models are developed for verification and established good correlation with the experimental response. The finite element analyses also provide an insight on the failure mechanisms. The results of this study can be further used towards the design and manufacture of practical grid stiffeners for the mechanical performance improvement.