Rate-dependent 3D forming simulation of thermoplastic composite materials using visco-hyperelastic material modeling and 3D hexahedral solid-shell elements

The Finite Element Method is a widely applied approach for predicting manufacturing effects in the thermoforming process of fiber-reinforced composite materials. The majority of macroscopic simulation approaches are based on shell elements with two-dimensional (2D) stress states and provide efficient predictions of the forming process of composite materials. However, they lack the ability to capture through-thickness behavior due to their dimensional limitations. The present study proposes a three-dimensional (3D) solid-shell element formulation that incorporates rate-dependent material modeling thus enabling the simulation of the thermoforming process of thermoplastic composites. The solid-shell element formulation provides a locking-free formulation, an hourglass stabilization technique to prevent zero-energy modes, a reduced integration scheme, and the consideration of a rate-dependent material behavior. An analysis of the correspondence between the material parameters of the 3D solid-shell element and an experimentally validated 2D approach indicates that the 2D approach can effectively be employed to characterize in-plane and bending material parameters for the 3D solid-shell element formulation, streamlining and accelerating its material parameter identification process. The parameterization of the nonlinear compaction behavior of the solid-shell element exhibits a strong correlation with experimental results from existing literature. Finally, the solid-shell element is utilized to simulate the thermoforming process of a thermoplastic tape, yielding results that closely match those obtained from a 2D approach. The predicted thickness distribution, determined by the new 3D solid-shell, agrees well with the expected results, confirming the validity and practical potential of the proposed approach.