Anisotropic atomistic shock response mechanisms of aramid crystals

Emily J Gurniak; Subodh C Tiwari; Sungwook Hong; Aiichiro Nakano; Rajiv K Kalia; Priya Vashishta; Paulo S Branicio

doi:10.1063/5.0102293

Anisotropic atomistic shock response mechanisms of aramid crystals

J Chem Phys. 2022 Jul 28;157(4):044105. doi: 10.1063/5.0102293.

Authors

Emily J Gurniak¹, Subodh C Tiwari², Sungwook Hong³, Aiichiro Nakano², Rajiv K Kalia², Priya Vashishta², Paulo S Branicio¹

Affiliations

¹ Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California 90089-0242, USA.
² Collaboratory for Advanced Computing and Simulations, Department of Physics and Astronomy, Department of Computer Science, Department of Chemical Engineering and Materials Science, Department of Biological Sciences, University of Southern California, Los Angeles, California 90089-0242, USA.
³ Department of Physics and Engineering, California State University, Bakersfield, Bakersfield, California 93311, USA.

PMID: 35922358
DOI: 10.1063/5.0102293

Abstract

Aramid fibers composed of poly(p-phenylene terephthalamide) (PPTA) polymers are attractive materials due to their high strength, low weight, and high shock resilience. Even though they have widely been utilized as a basic ingredient in Kevlar, Twaron, and other fabrics and applications, their intrinsic behavior under intense shock loading is still to be understood. In this work, we characterize the anisotropic shock response of PPTA crystals by performing reactive molecular dynamics simulations. Results from shock loading along the two perpendicular directions to the polymer backbones, [100] and [010], indicate distinct shock release mechanisms that preserve and destroy the hydrogen bond network. Shocks along the [100] direction for particle velocity U_p < 2.46 km/s indicate the formation of a plastic regime composed of shear bands, where the PPTA structure is planarized. Shocks along the [010] direction for particle velocity U_p < 2.18 km/s indicate a complex response regime, where elastic compression shifts to amorphization as the shock is intensified. While hydrogen bonds are mostly preserved for shocks along the [100] direction, hydrogen bonds are continuously destroyed with the amorphization of the crystal for shocks along the [010] direction. Decomposition of the polymer chains by cross-linking is triggered at the threshold particle velocity U_p = 2.18 km/s for the [010] direction and U_p = 2.46 km/s for the [100] direction. These atomistic insights based on large-scale simulations highlight the intricate and anisotropic mechanisms underpinning the shock response of PPTA polymers and are expected to support the enhancement of their applications.