Material Characterization and Finite Element Modeling for the Forming of Highly Oriented UHMWPE Thin-Film and Unidirectional Cross-ply Composites

Abstract

Thermoforming is a cost-effective, high-volume production process used for the manufacture of complex shaped thermoplastic composite parts. Finite element modeling of the process offers a cost-effective and time-saving tool to explore how changes in the ply stack-up orientations and processing conditions can impact part quality and throughput. A credible finite element model of the process requires a robust constitutive model of the material system and a comprehensive associated material characterization program to develop the set of material properties to go into that model. In this paper, some of the technical challenges associated with the charaterizaton of the in-plane shear mechanical behavior of two UHMWPE compsosite formats; a unidirectional fiber/matrix cross-ply (Dyneema® HB210) and a highly-oriented extruded film (DuPontTM TensylonTM HSBD 30A) and the subsequent finite element modeling of the shear response are explored. Picture frame shear testing of each material system is conducted to examine the mechanical behavior at room temperature and a processing temperature of 100°C. Trilinear and ploynomial empirical fits of the evolution of the in-plane shear stiffness as a function of the state of in-plane shear are derived from these experimental data. The curves are then used as material inputs for two material models in LS-DYNA, i.e. the built-in *MAT214 (*MAT_DRY_FABRIC) and *MAT41 (user-defined material model), respectively. The two material models are first used to investigate their respective abilities to replicate the material characterization shear-frame tests for Dyneema® HB210 and TensylonTM HSBD 30A and subsequently to model an in-plane shear test, which is a variation of the bias-extension test. Both material models correlate very well with the shear-frame test data for the two material systems and for the in-plane shear test of Dyneema® HB210. However, both material models underpredict the load deformation response for TensylonTM HSBD 30A. Future work is to understand what enhancements need to be added to the material models such that the in-plane shear response of TensylonTM HSBD 30A is better predicted by the models.