Session: 12-15-01: Dynamic Failure of Materials & Structures

Paper Number: 94754

94754 - Molecular Dynamics Simulation of Ultrahigh-Molecular-Weight Polyethylene Under High-Speed Impact 

This research aims to build a molecular dynamics simulation model with the objective of a fundamental understanding on the mechanics of ultra-high-molecular-weight-polyethylene (UHMWPE) fibers at atomic scales under extremely high-rate transverse impact loading condition. MD simulations of high-velocity impacts on carbon-based polymers are relatively rare. The most common materials studied are graphene sheet. In recent studies, ballistic impacts of polyethylene were studied via large-scale MD simulations to investigate the dissipated energy, deformation and fracture response, and temperature and pressure evolutions during impact. It was found that entanglement density, interchain friction, and chain mobility are influential factors on the ballistic behavior of the thin PE film. It was also observed that even under hypersonic speed impact, chain scission was not observed to be a significant mechanism in dissipating the energy of the PE film. These observations have provided important insight into the ballistic impact behavior of amorphous PE film. However, the microstructure of the impacted object is not a representative of real UHMWPE fiber. Another shortcoming of these simulation is that the exact role of each of these influential factors was not quantitatively analyzed. Therefore, in order to fully understand the underlying mechanisms of energy dissipation during ballistic impact, a highly representative MD model that takes into account the shish-kebab structure of the UHMWPE fiber is needed, which is the objective of this research. Therefore, in this research, ballistic impact simulation using molecular dynamics simulation method will be conducted for the UHWMPE fiber at microscale. Unlike most of the existing works, where the focus has been on the ballistic impact resistance of amorphous polyethylene, our research will consider exclusively the shish-kebab structure of the UHMWPE macro-fibril. Both the extended chain crystals that consist of the shish and epitaxial crystals that consist of the kebab will be investigated through molecular dynamics simulation method. In the ballistic impact simulations, a diamond projectile that represents a rigid projectile will be used to impact the polyethylene at various velocities. Two different types of potential energy function will be compared to reveal the energy dissipation mechanisms involved in the ballistic impact. The first type of potential energy function is given by the polymer consistent force field (PCFF) based on CFF91(consistent force field) with additional parameters specified for polymer materials. The PCFF and COMPASS (Condensed-phase Optimized Molecular Potentials for Atomistic Simulation Studies) force fields have the same functional form. The proposed MD simulation will be conducted by using the open-source MD code Large-scale Atomic/Molecular Massively Parallel Simulator (Lammps).

Presenting Author: Shah Alam Texas A&M University

Presenting Author Biography: Shah Alam is an assistant professor in the Department of Mechanical and Industrial Engineering at Texas A&M university-Kingsville. His research interests include Composite Structures Design and Analysis, Mechanical System Design and Analysis, Fatigue and Fracture Mechanics, Finite Element Analysis, Renewable Energy. Dr. Alam received his PhD in Mechanical Engineering from Louisiana State University (LSU) in 2005.

Authors:

Shah Alam Texas A&M University
Guodong Guo Texas A&M University -Kingsville