Pre-Impregnated Powder Coatings with a Thermoplastic Matrix for Use in Fibre-Reinforced Polymer Sandwich Composites: Manufacturing, Mechanical Testing and Finite Element Modelling.

This study presents a manufacturing route for pre-impregnated functional powder coatings (PCs) intended for fibre-reinforced polymer (FRP) composites, including vacuum-infused sandwich structures. PCs comprising powder, thermoplastic nonwoven and twill glass fabric were produced by a two-stage heat-pressing process. Ceramic, mineral and metallic powders were investigated. Uniaxial tensile tests with digital image correlation and three-point bending tests of PC-integrated sandwich composites were supported by finite element analyses of representative volume elements. Powder layers were parametrically generated in CadQuery for F24, F30 and F36 grains with ellipsoidal or sharp-edged geometries. The powder and thermoplastic layers markedly affected tensile stiffness and deformation. Apparent Young's moduli ranged from 3.8 to 8.1 GPa, compared with 11.7-14.3 GPa for reference specimens. Manufacturing-induced curvature and an atypical transverse response were attributed to the asymmetric layered architecture. All sandwich variants reached similar maximum bending loads of 0.93-0.96 kN, while absorbed energy ranged from 7.2 to 9.1 J. RVE simulations showed that grain size affected local stress, strain and displacement fields. The method enables repeatable manufacture of thin, modular functional layers and their integration with composites without applying loose powder during moulding.