Experimental characterization and numerical simulation of the automated fiber placement (AFP) process for thermoplastic fiber-reinforced plastics

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The efficient, high-quality and reproducible production of thermoplastic fiber-reinforced plastic components requires automated manufacturing processes. Due to its load-path oriented deposition of fibers to near-net-shape components, automated fiber placement (AFP) has particularly great potential. With proper temperature control during thermoplastic AFP (TP-AFP) in-situ consolidation is possible, i.e. a consolidation in place of the process without downstream thermosetting. However, the understanding of the process is still far from reaching the level of maturity necessary for a broad industrial application of TP-AFP. For example, it is still difficult today to define suitable process windows for the most important key parameters such as laser power, velocity and compaction pressure so that a consistently high quality of components is assured. In particular, the prediction of residual stresses and distortion is only solved insufficiently and process calibration is often based on a trial-and-error method. The reasons for this discrepancy between low prediction accuracy and high industrial demands can likewise be ascribed to possibilities of experimental characterization and modeling and simulation that are not yet maxed out. Therefore, the aim of the applicants is to improve process understanding in the area of TP-AFP fundamentally through novel experimental studies and methods of numerical simulation. On the experimental side, the focus will be on the integration of fiber optic sensors into the AFP process. For the first time, fiber Bragg grating (FBG) sensors will be used to monitor the characteristic TP-AFP process variables (consolidation pressure and laminate temperature) at key points, including within the laminate, thus allowing a reliable determination of the process-induced residual stresses subsequent to manufacturing. A long-term goal is the surveillance of the component in operation by so-called structure health monitoring (SHM). With respect to numerical simulation of the TP-AFP process, there is still a lack today of a holistic approach to reliably predict the critical component properties. Therefore, the focus in this project will be on the development and gradual integration of a corresponding overall process model based on nonlinear finite element methods (FEM). The aim is to achieve a significant improvement in prediction accuracy over the current state of research with this TP-AFP overall process model. Finally, the integration of experiment, modeling and simulation is also a particular feature of this project. For example, the simulation activities will consistently access the experimental results obtained in parallel so that all the sub-models can be appropriately parameterized. This integrated approach ultimately ensures the highest possible quality of the developed process model.