Virtual and experimental hybrid thermoforming of GFRP and aluminum

Abstract

In this work, a hybrid thermoforming process consisting of a glass fibre-reinforced thermoplastic and aluminum outer layers is investigated. To guarantee interlaminar adhesion of the two materials, a multi-layered thermoplastic adhesive film is used. Both materials are thermo-mechanically tested to calibrate the corresponding material model. In-plane tensile tests and bias extension tests, as well as out-of-plane cantilever tests, are used to characterize the behaviour of the organosheet. For the characterization of the aluminum alloy AA5182, uniaxial tensile tests at various temperatures and strain rates in relation to rolling direction are performed. A flat tool pressing process is chosen to show the flexural behaviour of the hybrid component in a three-point bending test, whereas lap shear tests are used to investigate the interlaminar shear strength carried by the adhesive film. In both validation experiments, it is shown that increased temperature and low applied pressure leads to increased flexural strength and interlaminar shear strength. A V-shaped two-dimensional geometry is used to apply this hybrid approach to a deep-drawing process. After the forming process, microscopic pictures of the cross-sections are manufactured to investigate the consolidation of the GFRP layer and evaluate air void formation. Being independent of the consolidation pressure, heating the GFRP layer up to 10 °C above melting temperature of the matrix material causes high void fraction and low fraction of bonding area between the GFRP and aluminum layer. Applying higher temperatures up to 280 °C leads to continuous bonding contact of all layers and only few and small void formations. Based on two simple geometries, a feasible hybrid thermoforming process of GFRP and aluminum is demonstrated.