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978-3-8439-3183-0, Reihe Ingenieurwissenschaften
Forming of tailored thermoplastic composite blanks: material characterisation, simulation and validation (Band 30)
238 Seiten, Dissertation Technische Universität München (2017), Softcover, A5
The increasing demand for composite components has driven the development of automated manufacturing processes. With their short manufacturing cycle time, thermoforming technologies appear to be good candidates for high volume production. Furthermore, they enable the manufacturing of complex parts which cannot be achieved with other automated techniques, e.g. AFP machines. Nevertheless, thermoformed composite blanks undergo severe deformations which can lead to the occurrence of defects, such as out-of-plane wrinkles and fibre reorientations. To investigate such issues, Finite Element (FE) simulations have demonstrated to be particularly efficient.
The goal of this PhD is to develop macroscopic FE thermoforming simulation models able to anticipate the occurrence of the aforementioned defects. Before being applied in an industrial context, models need to be validated. The reliability of their predictions is assessed by comparing computed outcomes to experimental measurements. In this work, validation is carried out with a generic double-curved component formed in a laboratory-scale thermoforming process.
To determine proper simulation input parameters, material behaviour is characterised under similar environmental conditions as forming occurs. The intrinsic behaviour of a unidirectional fibre-reinforced PA6 tape and a PI separation film are investigated. Contact properties are also investigated. To assess whether the test methods considered for molten thermoplastic composite materials are also suitable for non-cured thermoset composite materials, a non-cured unidirectional thermoset pre-impregnated composite tape is also characterised.
Thermoforming process simulation models are developed using a commercial software. Input parameters are identified from experimental data using an inverse method. Validation demonstrates the ability of the simulation to properly predict preform geometries and external fibre orientations. Results also show the ability of the simulation to determine areas where out-of-plane wrinkles can potentially occur, although their exact shapes and amounts cannot be predicted.
Two case studies are conducted with the developed simulation approach. The first one highlights the importance to model separation films as composite plies, i.e. with shell elements and a dedicated material model, while the second shows that the transverse tensile properties of the composite tape only have limited influence on simulation results.