Considering the viscoelastic material behavior in a solid-shell element for thermoforming simulation

Abstract. To predict manufacturing effects in the thermoforming process for fiber reinforced plastics the Finite Element Method is widely used. Most macroscopic simulation methods are based on conventional two-dimensional shell elements which are not capable of modeling the material behavior in thickness direction using constitutive equations. At the same time, standard three-dimensional element formulations are not suitable for the forming simulation of thin textiles due to numerical locking phenomena and the lack of a possible membrane-bending-decoupling. Previous studies focused on a specialized solid-shell element formulation which provides anisotropic but purely elastic material modeling. Since purely elastic approaches cannot accurately describe the deformation behavior in the thermoforming process, the provided element formulation is enhanced to rate-dependent viscoelastic material modeling. Numerical studies are carried out that reveal that the membrane-bending-decoupling is preserved for the viscoelastic material model. Virtual coupon tests demonstrate the rate-dependent material behavior in the solid-shell element. The obtained results show that the general approach of the viscoelastic material behavior within the solid-shell element is suitable to address out-of-plane phenomena in thermoforming simulations.