Axial-Compressive Behavior, Including Kink-Band Formation and Propagation, of Singlep-Phenylene Terephthalamide (PPTA) Fibers

M Grujicic,S Ramaswami,R Yavari,B A Cheeseman,C.-F Yen,J S Snipes

doi:10.1155/2013/329549

Abstract

The mechanical response ofp-phenylene terephthalamide (PPTA) single fibers when subjected to uniaxial compression is investigated computationally using coarse-grained molecular statics/dynamics methods. In order to construct the coarse-grained PPTA model (specifically, in order to define the nature of the coarse-grained particles/beads and to parameterize various components of the bead/bead force-field functions), the results of an all-atom molecular-level computational investigation are used. In addition, the microstructure/topology of the fiber core, consisting of a number of coaxial crystalline fibrils, is taken into account. Also, following our prior work, various PPTA crystallographic/topological defects are introduced into the model (at concentrations consistent with the prototypical PPTA synthesis/processing conditions). The analysis carried out clearly revealed (a) formation of the kink bands during axial compression; (b) the role of defects in promoting the formation of kink bands; (c) the stimulating effects of some defects on the fiber-fibrillation process; and (d) the detrimental effect of the prior compression, associated with fiber fibrillation, on the residual longitudinal-tensile strength of the PPTA fibers.

Highlights

Fibers of p-phenylene terephthalamide (PPTA), available commercially as Kevlar, Twaron, Technora, and so forth, are characterized by high specific axial stiffness and high specific tensile strength
The main objective of the present study is to extend our prior molecular-type simulation work [5,6,7,8, 14] in order to (i) provide insight into the phenomena and processes associated with the formation and propagation of kink bands within single PPTA fibers during axial compression
Since the work presented considers PPTA fibers which are initially either perfectly crystalline or crystalline but contain various defects, fibers which are subjected to tensile loading directly or after being subjected to a preludial axial compression and attention is paid to both defect-induced and compression-induced changes in the material microstructure and the longitudinal tensile strength, the corresponding results are presented and discussed within separate sections

Summary

Introduction

Fibers of p-phenylene terephthalamide (PPTA), available commercially as Kevlar, Twaron, Technora, and so forth, are characterized by high specific axial stiffness and high specific tensile strength These fibers are often referred to as “ballistic fibers” since they are commonly used in different ballisticand/or blast-protection systems. Such systems are required to provide a high level of penetration-resistance against largekinetic-energy projectiles, such as bullets, detonated-mineinduced soil ejecta, fragments/shrapnel from improvised explosive devices (IEDs), and shells or turbines. Given the complex behavior/functionality of the aforementioned protection systems, their design and development increasingly involve the use of computer-aided engineering (CAE) methods and tools The latter employ material models to describe the behavior of fibers and structures under high-rate loading conditions. With the utility of the CAE methods and tools largely determined by the fidelity of these models, their development must account for the hierarchical/multiscale architecture of the fibers-based structures, as well as of the fibers themselves [5,6,7,8]

Objectives

Results

Conclusion