Fundamentals about the impregnation of Dry Fiber Placement - Preforms

• Applicant: Privatdozent Dr.-Ing. David May
• Subject Area: Plastics Engineering
• Term: from 2017 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 347699788

In Liquid Composite Molding processes a fiber reinforced polymer composite is manufactured by impregnating a dry fiber preform with a liquid thermoset resin system. The innovative preforming technology Dry Fiber Placement (DFP) allows the manufacturing of a near-net-shape preform directly out of a roving within a single process step. For this a roving covered by thermoplastic binder is placed discontinuously on a tool surface at variable direction and position and fixed by temporary melting of the binder particles. This approach allows a high material efficiency by optimally load-related fiber positioning and practically zero-waste preforming. Yet, DFP-preforms show a severe disadvantage concerning their impregnation. The permeability, which describes the transmissibility for a liquid and therefore the impregnation behavior, is dramatically lower compared to woven or non-crimp fabrics. This results from the DFP-structure, which, contrary to woven or non-crimp fabrics, does not show any meso-scale flow channels (flow channels between rovings). These are highly relevant for the resin impregnation, since their permeability is several orders of magnitude higher than the permeability of micro-scale flow channels (flow channels within rovings, between single fibers). Hence, currently the industrial usage of DFP-preforms is not practicable.The target of the planned project is to research the basic correlations of DFP-preform impregnation. Based on this it is investigated how the permeability of DFP-preforms can be influenced by manipulating the fiber structure. For this, theoretical, simulative and experimental studies are synergistically combined to develop a holistic material model, which describes the permeability influence of various structural variations. This includes the following goals:1. Theoretical modelling of the local and global permeability influence of different structural variations2. Development of simulation models and extensive parameters studies on the structural variations3. Experimental investigation of the permeability influence as basis for the model validation4. Validation of the material models and the simulations by cross-comparison with experiments5. Development and validation of a holistic material model including influence given by superimposition of structural variations and by drapingSummarized, the focus of this project is on fundamental research regarding the permeability of DFP-preforms. Only with these validated fundamental findings, it is possible to realize active improvement of the impregnation behavior in industrial processes, e.g. within subsequent collaborative projects with industrial partners.

• DFG Programme: Research Grants