Effect of Boundary Conditions on the Back Face Deformations of Flat UHMWPE Panels.

摘要

The back face deformation (BFD) characteristics are important in assessing the load transfer from the helmet to the head due to blunt impact. We carried out a series of ballistic experiments to investigate the BFD in flat panels made of Ultra-High-Molecular-Weight-Polyethylene (UHMWPE). Spherical projectiles were used at velocities in which the panels were not perforated. In our study, we used three different boundary conditions, namely, clamped-corners, clamped-edges and free boundary condition (the panels are suspended by two strings). The experiments were modeled in LS-DYNA. Existing composite material models were found not to be adequate in capturing the observations. Therefore, we calibrated the constitutive parameters of a composite material model to the experimental conditions. Tiebreak contacts were used to model the delaminations in the composites. The calculation showed reasonable agreement with the experimental data for the clamped-corners and free boundary condition cases for the peak BFD, remaining thickness of the composite and the delamination behavior. The model is useful to assess the size-effects and boundary proximity effects under blunt impact scenarios.