Multi-scale modeling of the nonlinear damage behavior of carbon fiber reinforced thermoplastics

• Applicant: Professor Dr.-Ing. Jaan-Willem Simon
• Subject Area: Mechanics
• Term: since 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 423783552

Rising energy costs and growing climate protection requirements are leading to high demand for lightweight materials in vehicle construction. In particular, fiber-reinforced plastics are increasingly being used due to their high specific strength. In contrast to conventional thermosets, thermoplastic fiber-reinforced plastics (TPFRPs) offer the advantage that they can be repeatedly heated, formed and cooled. This results in various advantages such as short cycle times, increased toughness, easy storage and handling, and better recyclability, which have led to a growing market for thermoplastic systems for years. However, the material behavior of TPFRP is very complex and existing models are still insufficiently developed to cover all relevant aspects. Particularly, the prediction of damage behavior, which is essential for structural analysis, is not yet possible in many cases. Therefore, the overall objective of this research project is the development of a simulation tool for the prediction of damage progression and failure of TPFRP components. The consideration of the viscoelastic and viscoplastic properties of the thermoplastic matrix on the micro- and mesoscale, respectively, as well as the delamination of individual layers in the laminate prove to be necessary. The project work provides the following scientific innovations: First, a viscoelastic/viscoplastic material model of the thermoplastic is extended to include progressive damage, where these phenomena must be appropriately coupled. Furthermore, a novel homogenization concept is explored that is valid for large deformations and softening due to localization, where existing conventional approaches fail. With this formulation for the matrix behavior and the homogenization process, the microstructure (carbon fibers in thermoplastic matrix) and the mesostructure (textile fabric of carbon fiber bundles in thermoplastic matrix) are evaluated. The damage mechanisms considered include fiber breakage, matrix breakage, fiber (bundle)-matrix debonding, fiber or fiber bundle kinking, and delamination between individual layers. Using the proposed hierarchical multi-scale approach, a macroscopic material model for the composite is derived. The new macroscopic damage formulation captures the anisotropy of the composite material, is thermodynamically consistent, is valid also in the range of large deformations and is independent of the finite element discretization due to gradient expansion. The proposed modeling framework and simulation tool will allow to enhance the understanding of the failure of TPFRP components and the resulting predictions will enable appropriate design of structures made from TPFRP.

• DFG Programme: Research Grants
• International Connection: USA
• Cooperation Partners: Dr. Brett A. Bednarcyk; Evan Pineda, Ph.D.