Deduction of process-microstructure-property correlations of polymer-based additively manufactured structures by means of experimental and numerical analyses

• Applicants: Dr.-Ing. Wilfried Liebig; Dr.-Ing. Andreas Prahs; Dr.-Ing. Daniel Schneider
• Subject Area: Polymeric and Biogenic Materials and Derived Composites
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 565683135

Polymer-based additive manufacturing processes such as material extrusion (MEX) have undergone continuous technological development over the last two decades, resulting in the ability to process a wide range of several polymers, for example. This has contributed to the fact that the MEX process is not only used in model and prototype design, but also in the manufacturing of functional and structural components. However, additively manufactured components exhibit lower stiffness and strength compared to components produced with other manufacturing processes such as injection moulding. This can be attributed to four fundamental structural features: the interfaces between the individual tracks (within and between the layers), an increased waviness of the surface owing to the shape of the tracks, pores between the tracks (includes all types of pores) and the orientation of the tracks with regard to the load direction. The individual influences of the structural features are still the subject of current research and have not been sufficiently understood so far. The aim of the proposed project is therefore to analyse the influences of the structural features separately and to quantify their magnitude. In addition, the knowledge gained on the structural characteristics will be incorporated into a simulative modelling of additively manufactured structures in order to improve the prediction of mechanical properties in the future. For this purpose, the framework conditions such as thermal and rheological material parameters, the geometric formation of the tracks and the orientation of the molecular chains within a structure are first determined experimentally for two polymers (polyactides, PLA; amorphous and polyethylene terephthalate glycol, PET-G; semi-crystalline). Suitable specimen preparations and shapes are then developed in order to separately analyse the influences of the structural features. Finally, the effective stiffness and strength are characterised using the specimen shapes that have been defined. To determine the process-microstructure-property correlation, solidification simulation studies are carried out and the results are used for the numerical determination of the effective mechanical material properties. In order to enable large-scale simulation studies, a thermo-mechanically coupled simulation model is required that considers the interaction between heat conduction, solid mechanics and crystallinity, while taking large deformations into account. One of the main objectives is to investigate the influence of shrinkage owing to crystallisation during the solidification process. Finally, the results of the experimental and simulative investigations will be used to develop design guidelines for adapting the process parameters in order to optimise the effective material behaviour (stiffness and strength).

• DFG Programme: Research Grants
• Co-Investigator: Professorin Dr. Britta Nestler