Modeling of the fluid-structure interaction and prediction of possible pure resin areas in the mold filling of fiber composite sandwich components (FSI-Sandwich-2)

• Applicant: Professorin Dr.-Ing. Luise Kärger
• Subject Area: Plastics Engineering ; Lightweight Construction, Textile Technology
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 449100283

Sandwich components with cover layers made of fiber-reinforced plastics (FRP) and a very lightweight core material exhibit very high specific flexural stiffness and are therefore ideal for lightweight construction applications, e.g. in the aerospace or automotive sectors. In order to achieve the shortest possible process time with few production steps in a process suitable for large-scale production, the option of intrinsic sandwich component production using resin transfer molding (RTM) is available. For this, the foam core is placed between the dry semi-finished fiber products and then a liquid resin is injected under pressure in a heated mold. However, the pressure level during injection must be designed considering the mechanical properties of the sandwich core material in order to avoid plastic deformation of the core (1st project phase FSI-Sandwich) and detachment between the fibrous textile and the tool or core (2nd project phase FSI-Sandwich-2) during production. For the virtual design of the process, a mold filling simulation method was developed in the 1st project phase of FSI-Sandwich, which captures the fluid-structure interaction between the resin infiltration, the foam core and the fiber reinforcement deformation. In addition to the deformation of the foam core and the associated change in the fiber volume content, the detachment of the fiber reinforcement from the core and the formation of pure resin areas also have a major influence on the process and the component quality. Therefore, the FSI method is to be extended in the second project phase in order to map the deformations of the fluid domain and the fiber reinforcement separately, but with fluid-structure-mechanical interaction, to allow relative movement between the porous medium and the deformable fluid domain. The method development and validation are performed in two stages: First, the deformation of the fiber reinforcement by a rigid fluid domain is considered. In the second development stage, the movement of the textile is coupled to a deforming fluid domain, whereby the deformation of the fluid domain depends on the movements of the tool or the deformation of the foam core. The FSI interface is extended accordingly in order to be able to predict whether and to what extent the fiber reinforcement detaches from the tool or the foam core during the process. The method development is supported and validated by upstream characterization tests and material modelling of the dissipative fiber reinforcement deformation as well as subsequent validation tests.

• DFG Programme: Research Grants