Researcher(s)
- Iveena Mukherjee, , Charter School of Wilmington
Faculty Mentor(s)
- Nuwan Dewapriya, Center for Composite Materials, University of Delaware
Abstract
Ultra-high molecular weight polyethylene (UHMWPE) fibers are highly suitable for applications such as vests, helmets, and armor backing plates due to their low density and high specific tensile properties. The UHMWPE fiber consists of a heterogenous fibrillar structure, comprised of 17 µm fibers, and smaller nanoscopic fibrils within the fibers, with diameters in the order of 30 nm. Between these fibers exist ordered and disordered phases that connect fibers and are pertinent to the nanoscale mechanics of PE fibers. To model these phases, molecular dynamics simulations were performed using LAMMPS with the AIREBO-M potential. To model the effects of free surfaces and voids, we created several models. The first set of models was created to investigate the effects of free surfaces, and potential size-effects, resulting in 3 and 6 nm square periodic models. The second set of models included void models, with voids of 0.6 & 1.2 nm width and 5 nm length. This difference in void size resulted in different chain lengths (straight to curved), impacting material properties. Tensile test simulations were performed on these models at a strain rate of 109 s-1. It was found that the stress-strain curves of non-periodic models approach those of the periodic model as the model sizes increase, indicating closer resemblance to the bulk periodic model. For the void models, it was found that the presence of larger voids introduces longer wavy chains which results in an increase in stiffness. However, peak stress decreases in the presence of larger voids due to progressive failure, as straighter chains fail first.