Comparison of Bending Approaches for Thermomechanical Modeling of the Forming Process of Fiber-Reinforced Thermoplastics

Especially in the automotive and aerospace sector, lightweight materials have an important role in reducing weight and enhancing overall energy efficiency and performance. Due to the combination of their high mechanical properties with low densities, fiber-reinforced thermoplastics (FRTP) offer a high lightweight potential. For automotive applications, FRTPs are usually formed into shell-like components in the thermoforming process. Here a reliable process design relies on numerical models to capture the complex forming mechanisms accurately. However, most conventional solvers provide no accurate representation of the bending behavior of FRTPs. This limitation often results in inaccurate numerical results. Therefore, this paper introduces and systematically evaluates different modeling strategies for implementation of the bending response. Both continuum and multi-ply approaches are considered under isothermal and thermomechanical conditions. Two representative FRTP systems with polyamide 6 (PA6) matrices are investigated. A glass fiber-reinforced woven fabric and a unidirectional (UD) tape. The materials are comprehensively characterized with respect to their mechanical and thermal properties. Based on this data, material models are calibrated and implemented into numerical forming simulations of a highly double-curved double dome geometry. The forming behavior of the numerical model is evaluated against experimental results with a particular focus on the shear angle distribution. The study highlights the influence of the chosen bending formulation on numerical accuracy and provides guidance for improved thermomechanical forming simulations of FRTPs.