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

摘要

Thermoforming is a cost-effective, high-volume production process used for the manufactureof complex shaped thermoplastic composite parts. Finite element modeling of the process offers acost-effective and time-saving tool to explore how changes in the ply stack-up orientations andprocessing conditions can impact part quality and throughput. A credible finite element model ofthe process requires a robust constitutive model of the material system and a comprehensiveassociated material characterization program to develop the set of material properties to go intothat model. In this paper, some of the technical challenges associated with the charaterizaton ofthe in-plane shear mechanical behavior of two UHMWPE compsosite formats; a unidirectionalfiber/matrix cross-ply (Dyneema® HB210) and a highly-oriented extruded film (DuPontTMTensylonTM HSBD 30A) and the subsequent finite element modeling of the shear response areexplored. Picture frame shear testing of each material system is conducted to examine themechanical behavior at room temperature and a processing temperature of 100°C. Trilinear andploynomial empirical fits of the evolution of the in-plane shear stiffness as a function of the stateof in-plane shear are derived from these experimental data. The curves are then used as materialinputs 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 usedto investigate their respective abilities to replicate the material characterization shear-frame testsfor Dyneema® HB210 and TensylonTM HSBD 30A and subsequently to model an in-plane sheartest, which is a variation of the bias-extension test. Both material models correlate very well withthe 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 forTensylonTM HSBD 30A. Future work is to understand what enhancements need to be added to thematerial models such that the in-plane shear response of TensylonTM HSBD 30A is better predictedby the models.