Enhancing compressive strength of composite lattice intersection by symmetric ply interleaving

Composite lattice structures offer significant weight-saving potential owing to superior specific stiffness and strength. However, conventional lattice nodes with ply overlapping or drop-offs cause fibre waviness and discontinuities that compromise compressive strength. This paper introduces a novel symmetric ply interleaving concept for lattice nodes to enhance strength performance. The symmetric lattice intersections can be fabricated through a single-sided mould, simplifying the manufacturing of symmetric tapered laminates without compromising mechanical performance. Experiments on 8-ply laminate lattice showed the symmetric design improved compressive strength by 114% and 17% over the discontinuous and asymmetric design. A computational model was developed for lattice ribs to analyse the influence of rib thickness on strength and failure mechanisms. For ribs thinner than 12 plies, symmetric interleaved nodes fail by buckling, with matrix damage and delamination initiating in the tapering region. As rib thickness increases, structural stability is maintained until final material failure. For 16-ply ribs, the symmetric design achieved 84% and 50% higher strength than the asymmetric and discontinuous designs, respectively. Extending the model to Kagome-shaped lattice structures, the symmetric design showed improvements of 100% and 33% over the asymmetric and discontinuous configurations at 26 plies. These findings provide valuable insights for optimising composite lattice structures.