Characterizing Thermoplastic Shape-Memory Polymers for Mold Design: From Material Testing to Viscoelastic Modeling

The production of one-piece composite hollow profiles with undercuts presents significant challenges to conventional mould concepts. Mandrels made of thermoplastic shape-memorypolymers could facilitate demoulding and reduce tooling costs. To design moulds in a commercial environment, it is critical to determine their behaviour using off-the-shelf Finite Element Analysis (FEA) software. This work presents an easy to follow path from raw material to implementation of linear viscoelastic (LVE) material behaviour in commercial FEA software. The materials investigated are PA6, PET and PA11. Differential Scanning Calorimetry (DSC) is used to determine the glass transition, crystallization and melting temperatures of the materials. A Dynamic Mechanical Analysis (DMA) procedure is developed for combined frequency-sweeps and discrete temperature increments to determine the elastic modulus and shear modulus versus temperature and frequency. Parameters necessary for the implementation in the FEA software are derived from the DMA data by using fully open-source Python scripts. The applied methods allow for the generation and implementation of a LVE material model in off-the-shelf commercial FEA software. All methods are easily transferable to other thermoplastic and thermoset materials. In conclusion, the straightforward approach presented allows us to characterize viscoelastic polymers and implement their LVE behaviour in commercial FEA software in an accessible way.