Mesoscopic damage analysis of braided composites using mesh-superposition techniques for static failure and impact loading
Applied Mechanics, Statics and Dynamics
Final Report Abstract
In the present research project, the behavior of braided composites under quasi-static and impact loading was investigated. The studies included various braiding architectures (variations of braid angle and braid type) to evaluate their influence on the mechanical response. A particular focus was placed on the experimental analysis and numerical modeling of damage behavior. To this end, fracture mechanics characterization tests, Open-Hole Tension (OHT) tests, as well as Impact and Compression-After-Impact (CAI) tests were conducted. These experiments were accompanied by Digital Image Correlation (DIC), enabling the observation of local effects and providing insights into failure mechanisms and failure locations. In order to numerically predict the influence of the textile architecture, the method of mesh superposition was employed. In this approach, the matrix (master) and textile (slave) are meshed separately, superimposed and coupled using kinematic constraints. This separate meshing simplifies the model preparation process and reduces the time required, addressing a significant challenge traditionally associated with textile composite simulation. Furthermore, the mesh superposition method enables purely mesoscopic modeling, eliminating the need for a multiscale transfer from the mesoscale to the macroscale. This prevents scale-induced information loss and obviates the derivation of, for instance, phenomenological material models. However, the superposition approach introduces method-induced volumetric redundancy. This redundancy leads to additional stiffness and mass when assigning correct physical material properties, deviating from conventional finite element modeling. To account for this volume redundancy, a correction cycle was developed within the framework of explicit time integration. This cycle builds upon an existing continuum damage model for fiberreinforced composites and was implemented in the commercial FE solver LS-DYNA. The implementation is designed to avoid modifications to the material model itself, thereby providing a degree of generality that facilitates future application to other material models. For the actual correction, stiffness and mass adjustments are performed before and after the evaluation of the material law, resulting in stress and strain tensors equivalent to those obtained with conventional FE modeling. These tensors form the basis for damage analysis. Using the developed method, both quasi-static and impact loads could be simulated with high predictive accuracy. Compared to the current state of the art, significantly larger models can now be analyzed fully mesoscopically, allowing the investigation of complex load cases or local effects such as holes. Additionally, the method is not limited to braided structures only but can be applied to any type of textile preform to study the influence of fiber architecture on the mechanical response.
Publications
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Konferenzbeitrag: Mesoscopic Modeling of Braided Structures by Means of Laser Triangulation Measurement and Mesh Superposition Technique, TexComp-14, Kyoto, Japan, 14-16 September 2022.
Czichos, R. et al.
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Influence of fiber architecture variations on the mechanical behavior of carbon fiber braids subjected to quasi-static loads. Composites Part B: Engineering, 292, 112062.
Czichos, Ruben; Krischler, Ruben; Hering, Christoph & Middendorf, Peter
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Monographie: Beitrag zur numerischen Modellierung mesoskopischer Kohlenstofffasergeflechtstrukturen unter Berücksichtigung prozessinduzierter Variabilitäten, eingereichte Dissertation, Universität Stuttgart, Institut für Flugzeugbau, Stuttgart, 2025.
Czichos, R.
