Manufacturing, interfacial adhesion and mechanical investigations of inverse hybrid composite laminates: Carbon fibre-reinforced Polyamide-6/Aluminium

Inverse hybrid laminates consist of a metallic sheet sandwiched between two continuous fibre-reinforced thermoplastic composites. This class of structures can be tailored using specific sub-components combination to achieve a desired mechanical performance. The combination studied in the present work consist of an aluminium alloy sheet sandwiched between two carbon fibre-reinforced polyamide-6 thermoplastic composites (PA6CF/Alu/PA6CF). Inverse hybrid laminates are manufactured under a controlled cycle of time, temperature and pressure. Among the challenges in manufacturing this kind of hybrid laminates is the metal/composite interfacial adhesion. Metal/composite delamination take place upon the cooling step of manufacturing process is finished. To prevent this phenomenon functionalized thermoplastic foil adhesion promoters are used in combination with a mechanical treatment of the aluminium alloy sheet surfaces. In this regard two commercial adhesion promoters are used and their performances are compared through inverse hybrid laminates mechanical testing: monolayer adhesive foil based on functionalized polypropylene (PP) and a second one based on functionalized polypropylene/polyamide (PP-PA). Three-point bending, tensile and interlaminar shear strength tests are conducted to evaluate the mechanical performances and failure modes of the manufactured inverse hybrid laminates and compared to those of the carbon fibre-reinforced thermoplastic composite. The inverse hybrid laminates bonded with the polypropylene-based foils results in enhanced mechanical performances relative to the ones bonded with the polypropylene/polyamide foils e.g. ∼10% higher tensile strength, ∼20% higher bending stiffness and ∼12% higher bending strength along the fibres. Regarding to the three-point bending tests inverse hybrid laminates failure reveals a strong aluminium/composite adhesion. While the tensile tests demonstrate that the adhesion foils deprive the hybrid laminates delamination, ehe interlaminar shear strength tests impart a ductile behaviour preventing a shear failure of the inverse hybrid laminates. • Manufacturing of inverse hybrid laminates with controlled time-temperature-pressure cycle. • Aluminum/PA6CF Interfacial adhesion promoters avoid the delamination failure under the bending loading and limit failure propagation along the fibre’s direction under tensile loading. • Mechanical characterisations of the hybrid laminates are dominated by the PA6CF properties. • The interlaminar shear strength tests impart a ductile behaviour preventing a shear failure of the hybrid laminates.