Study on the connection process and mechanical properties of double-layer GF/PP sandwich structure

Although multi-layer thermoplastic composite sandwich structures retain the inherent advantages of thermoplastic materials, their low interlaminar load transfer efficiency and susceptibility to delamination significantly hinder improvements in static mechanical properties. This study investigates a hybrid interlaminar connection process that combines hot-melt connection and mechanical fastening to enhance the mechanical properties of continuous glass fiber-reinforced polypropylene (GF/PP) honeycomb sandwich panels. Single-lap shear, three-point bending, and edgewise compression tests were conducted to evaluate performance. Results demonstrate that the hybrid connection significantly outperforms individual methods or adhesive film and mechanical combinations. The shear strength reached 4.45 MPa, representing a 69.20% enhancement compared to the hot-melt connection alone. This significant improvement is attributed to the effective Z-direction reinforcement and mechanical fastening provided by the GF/PP columns. The bending stiffness and the edgewise compression strength reached 261.95 N·m² and 14.91 MPa, reflecting improvements of 84.46% and 41.06% over hot-melt, and 35.88% and 33.72% over adhesive film and mechanical hybrids, respectively. These results confirm that this hybrid connection process effectively improves the structural stiffness and interlaminar connection strength of the double-layer sandwich structure through the synergistic effects of the high-strength hot-melt layer and mechanical fastening.