Polymer crystallization significantly influences the mechanical and thermal properties of components manufactured through processes such as extrusion and injection molding. This dependence arises due to the morphology and degree of crystallization attained during these processes, which are pivotal in determining the effective thermomechanical properties of components made from semi-crystalline polymers. Recognizing the non-local character of the crystalline structure in these materials, our research aims to investigate the evolution of crystalline grains within semi-crystalline polymeric matrices and their composites. Using the multiphase-field approach [1], our study tracks the evolution of individual crystalline grains with the crystallinity as the driving force for the phase-field evolution. The crystallinity of each grain dynamically evolves following an Avrami-type model [2]. Since polymer crystallization is exothermic in nature, the model is coupled with the heat conduction equation using a latent heat contribution. This coupled approach allows for a better understanding of the interplay between the evolution of temperature and the crystalline phase. Moreover, regarding polymer-based composites such as GFRP (Glass fiber reinforced polymer) and CFRP (Carbon fiber reinforced polymer), the evolution of crystallinity in the vicinity of the fibers is investigated. Thereby, the effect of the presence of the fiber on the degree of crystallinity is discussed.

The findings of this research have practical implications for improving the manufacturing and performance of polymer-based products, contributing to more informed material design and processing strategies.