Numerical modeling of the influence of mechanical recycling on fiber-reinforced thermoplastics

Fiber-reinforced thermoplastics (FRTPs) offer an attractive combination of mechanical performance and recyclability. Yet mechanical recycling alters their microstructure and degrades material properties. This study presents a multiscale modeling approach to quantify the impact of mechanical recycling on the nonlinear mechanical behavior of a glass fiber-reinforced polypropylene composite. Using high-resolution CT scans and incineration analysis, fiber geometry - including orientation, length distribution, and volume fraction - was characterized for virgin and mechanically recycled material. Representative volume elements (RVEs) generated from this data served as the basis for microscale simulations, which accurately predicted the degradation in stiffness and the nonlinear stress response observed experimentally. An automated calibration procedure for anisotropic LS-DYNA material cards was developed based on virtual tests of the RVEs, enabling predictive macroscale simulations without extensive experimental input. The approach was validated against component-level bending tests, demonstrating its capability to capture complex load responses of recycled FRTPs. This work provides a cost-effective and reliable framework for process-aware modeling and predictive simulation of recycled fiber-reinforced composites, enabling efficient determination of recycled material properties and thereby supporting circular economy.