Significance of the material parameters within a three-dimensional solid-shell element for thermoforming simulation

In this study, a hexahedral solid-shell element is employed for the simulation of the thermoforming processes for unidirectionally reinforced thermoplastic tapes. This allows for the direct application of a fully three-dimensional material behavior, in contrast to conventional two-dimensional approaches that neglect thickness deformations. However, the additional material parameters increase the computational effort during characterization. It is therefore crucial to distinguish the material parameters that have a significant influence on the final forming result from those that have a negligible impact. The results reveal that rate-dependent material modelling has the most significant influence on the final forming results. Therefore, it is crucial to accurately model the viscoelastic behavior to simulate thermoforming appropriately. Furthermore, the material parameters that describe the in-plane tension behavior are relevant for accurately predicting the material draw-in. The transverse shear stiffnesses for both the membrane and the bending behavior show low significance due to the low laminate thicknesses. Similarly, low bending stiffnesses, e.g., the elastic bending perpendicular to the fiber direction, are also of negligible significance compared to the high rate-dependency in those deformation modes.