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Title: Molecular dynamics modeling of PPTA crystallite mechanical properties in the presence of defects

Here, the mechanical properties of PPTA crystallites, the fundamental building blocks of aramid polymer fibers such as Kevlar® and Twaron®, are studied here using molecular dynamics simulations. The ReaxFF interatomic potential is employed to study crystallite failure via covalent and hydrogen bond rupture in constant strain-rate tensile loading simulations. Emphasis is placed on analyzing how chain-end defects in the crystallite influence its mechanical response and fracture strength. Chain-end defects are found to affect the behavior of nearby chains in a region of the PPTA crystallite that is small relative to the typical crystallite size in manufactured aramid fibers. The central Csingle bondN bond along the backbone chain is identified as the weakest in the PPTA polymer chain backbone in dynamic strain-to-failure simulations of the crystallite. It is found that clustering of chain-ends leads to reduced crystallite strength and crystallite failure via hydrogen bond rupture and chain sliding, whereas randomly scattered defects impact the strength less and failure is by covalent bond rupture and chain scission. The axial crystallite modulus increases with increasing chain length and is independent of chain-end defect locations. On the basis of these findings, a theoretical model is proposed to predict the axial modulus as a functionmore » of chain length.« less
Authors:
ORCiD logo [1] ;  [2] ;  [3]
  1. Univ. of California, Berkeley, CA (United States); Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  2. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  3. Univ. of California, Berkeley, CA (United States)
Publication Date:
Report Number(s):
LLNL-JRNL-717003
Journal ID: ISSN 0032-3861
Grant/Contract Number:
AC52-07NA27344
Type:
Accepted Manuscript
Journal Name:
Polymer
Additional Journal Information:
Journal Volume: 114; Journal Issue: C; Journal ID: ISSN 0032-3861
Publisher:
Elsevier
Research Org:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
42 ENGINEERING; 36 MATERIALS SCIENCE; Kevlar®; Aramid fibers; elastic modulus; defects; molecular dynamics; reactive potentials
OSTI Identifier:
1351138
Alternate Identifier(s):
OSTI ID: 1396502