Modeling failure mechanisms of poly(p-phenylene terephthalamide) fiber using reactive potentials

Yılmaz, Dündar E.

doi:10.1016/j.commatsci.2015.07.010

Cited by 24 publications

(25 citation statements)

References 30 publications

(44 reference statements)

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“…Quantities measured include the simulation cell dimensions, bond lengths and angles, and aromatic ring orientations as represented by their time-averaged plane normal direction cosines. These time-averaged quantities are reported in Table 3 It is worth noting that a recently published MD study of PPTA [79] also employed the ReaxFF force eld, but used the parameterization of Strachan et al [69]. In the simulations conducted here, it was observed that running an equilibration simulation using the Strachan parameterization led to an inaccurate equilibrium crystal cell geometry.…”

Section: Unit Cell Geometrymentioning

confidence: 82%

Molecular Dynamics Modeling of PPTA Crystals in Aramid Fibers

Mercer

2016

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In this work, molecular dynamics modeling is used to study the mechanical properties of PPTA crystallites, which are the fundamental microstructural building blocks of polymer aramid bers such as Kevlar. Particular focus is given to constant strain rate axial loading simulations of PPTA crystallites, which is motivated by the rate-dependent mechanical properties observed in some experiments with aramid bers. In order to accommodate the covalent bond rupture that occurs in loading a crystallite to failure, the reactive bond order force eld ReaxFF is employed to conduct the simulations.Two major topics are addressed: The rst is the general behavior of PPTA crystallites under strain rate loading. Constant strain rate loading simulations of crystalline PPTA reveal that the crystal failure strain increases with increasing strain rate, while the modulus is not aected by the strain rate. Increasing temperature lowers both the modulus and the failure strain. The simulations also identify the CN bond connecting the aromatic rings as weakest primary bond along the backbone of the PPTA chain. The eect of chain-end defects on PPTA micromechanics is explored, and it is found that the presence of a chain-end defect transfers load to the adjacent chains in the hydrogen-bonded sheet in which the defect resides, but does not inuence the behavior of any other chains in the crystal. Chain-end defects are found to lower the strength of the crystal when clustered together, inducing bond failure via stress concentrations arising from the load transfer to bonds in adjacent chains near the defect site. The second topic addressed is the nature of primary and secondary bond failure in crystalline PPTA. Failure of both types of bonds is found to be stochastic in nature and driven by thermal uctuations of the bonds within the crystal. A model is proposed which uses reliability theory to model bonds under constant strain rate loading as components with time-dependent failure rate functions. The model is shown to work well for predicting the onset of primary backbone bond failure, as well as the onset of secondary bond failure via chain slippage for the case of isolated non-interacting chain-end defects.

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Section: Unit Cell Geometrymentioning

confidence: 82%

Molecular Dynamics Modeling of PPTA Crystals in Aramid Fibers

Mercer

2016

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“…The primary challenge with using ReaxFF is choosing a suitable parameter set to model PPTA, as no parameterization has been developed specifically for aromatic polyamides. A recent MD study [34] used the parameterization of Strachan et al [35] for modeling both amorphous and crystalline phases of PPTA. However, our early simulations showed that this parameter set was not able to replicate the basic PPTA crystal structure (see Figure 1) at room temperature.…”

Section: Force Field Selectionmentioning

confidence: 99%

“…The PPTA crystal lattice with pseudo-orthorhombic unit cell 33,34 . Figure 17: Normalized link strain (relative to nominal levels in a perfect crystal) in PPTA chains for a system with a small crack, as illustrated in Figure 16a.…”

Section: Appendix a Derivation Of Elastic Moduli For Crystallite Withmentioning

confidence: 99%

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

Mercer

Zywicz

Papadopoulos

2017

Polymer

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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 C-N bond along the backbone chain is identified as the weakest in the PPTA polymer chain backbone in dynamic strain-to-failure simulations of the *

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“…They reported that the tensile properties were unchanged under small amounts of pre-compression (~5% strain). Recently, Yilmaz et al [23] and Mercer et al [24] have studied the anisotropic elastic and strength properties of Kevlar ® crystal using reactive force field ReaxFF [27]. O'Connor et al [25] have studied the effects of chain ends on the elastic and strength properties of PE crystal using a modified version of reactive force field AIREBO (Adaptive Intermolecular Reactive Empirical Bond Order) [28].…”

Section: Introductionmentioning

confidence: 99%

“…The effect of AC and TC deformation modes on the fiber tensile failure strength has not been studied extensively. There are few atomistic simulations studies [20][21][22][23][24][25] that focused on the elastic and strength properties of Kevlar ® and PE crystal. Rutledge et al [20] have determined the elastic properties of Kevlar ® crystal through atomistic simulations.…”

Section: Introductionmentioning

confidence: 99%

Molecular Dynamics Modeling of the Effect of Axial and Transverse Compression on the Residual Tensile Properties of Ballistic Fiber

Chowdhury

Sockalingam

Gillespie

2017

Fibers

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Ballistic impact induces multiaxial loading on Kevlar ® and polyethylene fibers used in protective armor systems. The influence of multiaxial loading on fiber failure is not well understood. Experiments show reduction in the tensile strength of these fibers after axial and transverse compression. In this paper, we use molecular dynamics (MD) simulations to explain and develop a fundamental understanding of this experimental observation since the property reduction mechanism evolves from the atomistic level. An all-atom MD method is used where bonded and non-bonded atomic interactions are described through a state-of-the-art reactive force field. Monotonic tension simulations in three principal directions of the models are conducted to determine the anisotropic elastic and strength properties. Then the models are subjected to multi-axial loads-axial compression, followed by axial tension and transverse compression, followed by axial tension. MD simulation results indicate that pre-compression distorts the crystal structure, inducing preloading of the covalent bonds and resulting in lower tensile properties.

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Modeling failure mechanisms of poly(p-phenylene terephthalamide) fiber using reactive potentials

Cited by 24 publications

References 30 publications

Molecular Dynamics Modeling of PPTA Crystals in Aramid Fibers

Molecular Dynamics Modeling of PPTA Crystals in Aramid Fibers

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

Molecular Dynamics Modeling of the Effect of Axial and Transverse Compression on the Residual Tensile Properties of Ballistic Fiber

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