A MOLECULAR DYNAMICS-BASED ANALYSIS OF THE INFLUENCE OF STRAIN-RATE AND
TEMPERATURE ON THE MECHANICAL STRENGTH OF PPTA CRYSTALLITES
B. Mercer, E. Zywicz, and P. Papadopoulos
to appear in Polymer
Molecular dynamic simulations are used to quantify how the mechanical behavior
of PPTA crystallites, the fundamental building blocks of aramid fibers such
as Kevlar, depend on strain-rate, temperature, and crystallite size.
The (axial) crystallite elastic modulus is found to be independent of
strain-rate and decreases with increasing temperature.
The crystallite failure strain increases with increasing strain rate and
decreases with increasing temperature and crystallite size.
These observations are consistent with crystallite failure being driven
by stress-assisted thermal fluctuations of bonds within PPTA crystallites
and the concepts of the kinetic theory of fracture.
Appealing to reliability theory, a model is proposed that predicts the onset
of both primary and secondary bond failure within a crystallite as of function
of strain rate, temperature, and crystallite size.
The model is parameterized using bond failure data from constant strain-rate
molecular dynamic strain-to-failure simulations and is used to compute
the activation volume, activation energy, and frequency for both primary
and secondary bond ruptures.
for a preprint of this article.)