On the applicability of thermoforming characterization and simulation approaches to glass mat thermoplastic composites

Chopped fiber composite materials offer the potential to be used for complex geometries, including local thickness changes, ribs and beads, offering significant potential for functional lightweighting. Depending on the initial mold coverage and flowability of the material, the processing behaves either more like a compression molding or a thermoforming process. The latter is applicable to high initial mold coverages and includes typical thermoforming defects such as local wrinkling. Such defects are not predictable by conventional compression molding simulation approaches usually adopted for this material class. Therefore, thermoforming characterization and simulation approaches and their applicability to glass mat thermoplastic (47 vol.% long glass fiber, Tepex Flowcore) for high initial mold coverages is investigated. Abaqus in combination with several user-subroutines is applied. Valid material characterization results from torsion bar and rheometer bending tests are obtained and applied to an automotive structure in thermoforming simulation. Results indicate that the high stiffness and high viscosity captured by the rheometer bending test at low shear-rates are necessary to reproduce the wrinkling behavior observed in the experimental results. Discrepancy is most likely reducible to thermomechanical effects, and that the modelling approach does not account for thickness deformation due to transverse compression.