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Umformsimulation für vernähte Fasergelege (NCF) basierend auf Ansätzen generalisierter Kontinua

Fachliche Zuordnung Leichtbau, Textiltechnik
Förderung Förderung von 2019 bis 2024
Projektkennung Deutsche Forschungsgemeinschaft (DFG) - Projektnummer 431354059
 
Erstellungsjahr 2024

Zusammenfassung der Projektergebnisse

Continuously carbon fiber reinforced composites are increasingly used for structural applications in various fields of engineering due to their excellent weight-specific mechanical properties. Non-crimp-fabrics (NCF) provide the highest lightweight potential as reinforcement for the composite due to their straight fibers, compared to woven fabrics with undulated fibers. NCFs are made of one (UD-NCF), two (Biax-NCF) or more directions of fibers linked together with a polymer stitching in specific patterns. The deformation behavior of NCFs is challenging due to the interaction between the fibers and the stitching, which also results in a higher susceptibility to forming effects such as roving slippage, fiber waviness and gapping compared to woven fabrics. The aim of the AMECOMP project was to improve the understanding of the forming behavior of NCFs and to develop suitable simulation models to broaden the range of potential applications. Mesoscopic models that accurately describe the architecture of the NCF were developed for virtual material characterization and detailed analysis of forming defects in critical areas. Macroscopic models were developed for efficient analysis of large components and multi-layer stacks by describing the relevant deformation mechanisms of NCF in a homogenized way. For both models, approaches based on generalized continuum mechanics were explored to improve their accuracy and to overcome the limitations of conventional approaches based on Cauchy mechanics, which cannot simultaneously express the bending stiffness of the single fibers (microscopic stiffness) and the slippage between the fibers. A comprehensive experimental database was established for the different deformation mechanisms and forming behavior of commercially relevant UD- and Biax-NCFs. Experimental tests on isolated fiber rovings and stitching were combined with CT measurements of the textile architecture. Experimental coupon tests for the membrane, bending, out-of-plane compaction and friction behavior were conducted to determine the homogenized material properties. A parametric mesoscopic Finite-Element model of Biax-NCF was developed based on the real geometry from tomography results. The model can be easily adjusted for new fabric architectures and incorporates the roving bending stiffness based on a superimposed beam element approach. For UD-NCF, a mesoscopic forming model was developed with the ability to investigate local deformations such as slippage between fiber rovings and the formation of gapping. A macroscopic forming model for UD-NCF was developed based on a hyper-elastic approach that accounts for superimposed shear, transverse tension and in-plane compression of the fiber rovings. The new model requires significantly fewer material parameters than existing approaches to simplify its parameterization and facilitate its transferability to other materials, as demonstrated for Biax-NCF. A three-dimensional solid-shell-element for Finite-Element forming simulations of textiles was developed, that accounts for a decoupled membrane and bending behavior of fibrous materials based on the idea of a second gradient approach. The new element formulation can account for out-of-plane compaction during forming to predict the final thickness and consequently fiber volume content, in contrast to existing approaches mainly based on two-dimensional formulations. The reliability and accuracy of the mesoscopic and macroscopic models were validated by comparison to experimental forming tests of different geometries, different initial fiber orientations and layup configurations. Optical measurement techniques were used to ensure quantitative agreement of the final fiber orientation, strain distributions and gapping. The AMECOMP project has resulted in two completed doctoral dissertations and twelve international peer-reviewed publications, four of which appeared in peer-reviewed journals and eight in peer-reviewed conference proceedings, accompanied by oral presentations.

Projektbezogene Publikationen (Auswahl)

 
 

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