An anisotropic thermo-mechanically coupled constitutive model for glass fiber reinforced polyamide 6 including crystallization kinetics

In order to achieve process stability in the industrial thermoforming of fiber reinforced polymers (FRPs), typically, cost- and time-intensive trial-and-error-processes are required. The experimental boundary conditions, as well as the material composition and component design optimization, are highly dependent on material phenomena related to various material scales and constituents. It is therefore necessary to develop finite element constitutive models that are validated against experimental results and incorporate various material phenomena in order to reduce the experimental effort and evaluate the composite’s performance with reliable predictions. In this work, an existing thermo-mechanically coupled constitutive model for polyamide 6 is extended in a thermodynamically consistent manner to represent the anisotropic composite behavior, including anisotropic conduction, thermal expansion as well as internal heat generation associated with irreversible processes. Furthermore, the crystallization process is incorporated using experimental standard (S-DSC) and flash (F-DSC) differential scanning calorimetry results. The thermal and mechanical model parameters of the homogenized macroscopic material formulation are identified and the model response is successfully validated with a data base comprising both experimental and virtual results. Finally, the model capabilities are assessed in several thermo-mechanical structural computations, including a 3D thermoforming example in comparison with experimental results. In particular, the influence of the anisotropy on material self-heating, thermal expansion and the resulting crystalline state is investigated, demonstrating the potential of this new approach to efficiently and accurately predict FRPs in the future. Our source code, data, and exemplary input files are available under https://doi.org/10.5281/zenodo.15052983.