Modeling of a Cross-Ply Thermoplastic for Thermoforming of Composite Sheets in LS-DYNA ®

Thermoforming is a very attractive process for the cost-effective high-volume production of high-performance composite parts. The process starts with an open-punch tool to produce a set of preforms. The preforms are then consolidated into a part using matchedtooling high-pressure compression molding. However, this process is prone to the formation of defects such as wrinkling of the plies as they conform to the compound-curvature geometries of the tool and poor consolidation of the set of preforms due to non-uniform thickness of the preforms. Thus, the processing options must be well understood, so the composite manufacturing process can be designed to mitigate wrinkling and to achieve full consolidation and thereby produce high-quality parts. The finite element method is well suited to give insight into how changes in the processing parameters such as binder pressure, temperature, tool speed, material properties and ply/ply and tool/ply frictions can impact part quality. A robust finite model can predict if and where wrinkles may precipitate and the degree of consolidation for a given set of process settings. Such a robust model requires a complete characterization of the mechanical behaviors of the material systems. The current research uses the temperature-dependent material properties of Dyneema® HB80, a cross-ply lamina sheet, and DuPontTM TensylonTM HSBD 30A, a bidirectional laminate tape, both known for their excellent ability to dissipate energy during impact, as inputs to a user-defined material model for LS-DYNA simulations. A hybrid discrete mesoscopic approach is employed to simulate the tensile and shear frame experimental characterization tests. Finite element simulations of the characterization experiments are compared to experimental results of the same to validate that the user-defined material model can replicate the experiments from which the material constants were derived. The current work shows excellent agreement between the model and the results from tensile and shear-frame experiments. Future work will incorporate material bending and ply/ply and tool/ply frictions. The ultimate goal is for the procedures that are used for conducting the material characterizations and for the process simulations that are developed in this research to be integrated into a Virtual Design Framework, where the part will be designed, manufactured and “tested” for field performance using a set of well-connected CAD/CAE tools, thereby minimizing the dependence on the design-build-test methodology.