Optimization study on wet electrostatic powder coating process to manufacture UHMWPE/LDPE towpregs

In the present study, an attempt has been made to coat the non-conductive Ultra-high Molecular Weight Polyethylene (UHMWPE) fibers with Low-Density Polyethylene (LDPE) powder. In order to enable the deposition of electrostatically charged LDPE powder onto the fiber surface, UHMWPE fibers are dipped into a surface modification bath to impart momentary conductivity. Further, Box Behnken’s experimental design is used to optimize the processing parameters for Fiber Volume Fraction (Vf) for this wet electrostatic spray coating process. An experimental multi-parametric equation is acquired through response surface methodology to ascertain the association amid the process parameters such as processing temperature (A), conveying air pressure (B), and gun nozzle angle (C) on the output response of Vf. The process parametric values for A, B, and C are varied from 225°C to 245°C, 0.2 bar to 0.4 bar, and 0° to 120° respectively. The Vf obtained is in the range of 37.02%–56.28% depending on the combination of process parametric values. Powder pick-up increases with an increase in the gun nozzle angle. An increase in conveying air pressure and temperature of the hot air oven leads to an increase in powder deposition. The values predicted from the model are observed to be in close proximity (94.59%) to the experimental results. Gun nozzle angle is the principal parameter affecting the matrix deposition on the fiber surface in comparison to other process parameters.

Perforation mechanics of UHMWPE soft ballistic sub-laminate and soft ballistic armor pack: A finite element study

Soft-ballistic sub-laminate (SBSL) made from ultra-high molecular weight polyethylene (UHMWPE) fibers in [0/90] stacking sequence are the building block of a multi-layer soft-ballistic armor pack (SBAP, aka Soft Armor). A systematic study of the perforation dynamics of a single layer SBSL and several multi-layer SBAPs (2, 3, 4, 8, 16, 24, 32 layers) is presented for the first time in the literature. A previously validated finite element model of transverse impact on a single layer is used to study the perforation mechanics of multi-layer SBAPs with friction between individual layers. Following the classical definition of ballistic limit velocity, a minimum perforation velocity has been determined for free-standing single layer SBSL and multi-layer SBAPs. For the multi-layer SBAPs, complete perforations have been identified as progressive perforation of individual layers through the thickness. The minimum perforation velocities of multi-layer SBAPS is linear with the areal density for the eight (8) layer target and thicker. Large deformation behavior and perforation mechanics of the SBAPs is discussed in detail.