Strain-dependent dynamic mechanical properties of Kevlar to failure: Structural correlations and comparisons to other polymers

Abstract

The processing of Kevlar to certain strengths by hot-drawing can benefit by quantitative understanding of the correlation between structural and mechanical properties during the pre-drawing process. Here, we use a novel continuous dynamic analysis (CDA) to monitor the evolution in storage modulus and loss factor of Kevlar 49 fibers as a function of strain via a quasi-static tensile test. Unlike traditional dynamic mechanical analysis, CDA allows the tracking of straindependent mechanical properties until failure. The obtained dynamic viscoelastic properties of Kevlar 49 are correlated with structural data obtained from synchrotron radiation analysis and with Raman scattering frequencies. Ratedependent stress-strain results from Kevlar are compared to Nomex, spider silk, polyester and rubber, and provide insight into how the mechanical properties of Kevlar originate from its characteristic structural features. We find that as the storage modulus of Kevlar is essentially equal to the Young's modulus, the measured quantitative relationships between storage modulus and strain can provide insights into the tuning of the mechanical properties of aramid materials for specific applications. On the other hand, the technique of continuous dynamic analysis (CDA) combines the advantages of dynamic mechanical analysis with those of the quasi-static tensile test to quantify the evolution of viscoelastic properties as a continuous function of strain [4]. This is achieved through application of a small harmonic (20 Hz) strain during the tensile deformation. Because the harmonic strain is much smaller in magnitude than the applied quasi-static strain, it remains within the limits of linear viscoelasticity and does not affect the behavior of a quasi-static tensile test. Here, using a specialized electromechanical load cell capable of applying small but continually increasing periodic forces, we employ CDA to monitor the dynamic properties of Kevlar 49 fibers as a function of their strain to failure. We then quantitatively correlate our results to the structural tensile data of Kevlar from previous studies utilizing wide-angle X-ray diffraction (WAXD) [5] and Raman spectroscopy [6], to provide insight into the molecular mechanisms by which Kevlar tolerates stress. The dynamic mechanical behavior of Kevlar is further compared to those of other key structural polymers to quantitatively discern its dynamic responses against known benchmarks. As such, this study presents quantitative information on how the drawing of Kevlar changes its mechanical properties, thereby providing guidelines for the systematic optimization of this important engineering fiber.

Influence of corona discharge on the surface and thermal properties of aramid fabrics

“…The fibers surfaces in the reference mAr (Figure a) and pAr (Figure b) fabrics is uneven with visible lengthwise cracks. Aramids fibers have a fibrillar and pleated structure with bundles . There are no significant changes in topography after corona discharge treatment for mAr fabric.…”

Cavitation-Induced Stiffness Reductions in Quantum Dot–Polymer Nanocomposites

“…22,[35][36][37] This clearly is to be expected from a rule of mixtures analysis 4,7,13,[23][24][25][26][27] owing to the much higher Young's modulus of the filler. 1,3,5,8,10,22,[28][29][30][31] Fewer studies have shown the opposite effect, that of a reduction in Young's modulus.…”

“…Most studies on nanocomposites fillers reveal a progressive increase in modulus with increasing reinforcement volume fractions; examples of studies in polymers include claybased nanocomposites, [12][13][14]19,20 microscale ceramic TPs and needles, 15,16,21 graphene, 17,22 carbon nanotubes, 13,18,[23][24][25][26][27] carbon black, 3,8,10,19,20,22,[28][29][30][31] glass fibers, 3,8,10,21,32-34 and others. 22,[35][36][37] This clearly is to be expected from a rule of mixtures analysis 4,7,13,[23][24][25][26][27] owing to the much higher Young's modulus of the filler.…”

Influence of three-dimensional nanoparticle branching on the Young’s modulus of nanocomposites: Effect of interface orientation

“…Here, using nanorods (NRs) and tetrapod quantum dots (tQDs) in both electrospun fibers and solvent-cast films, we study the effect of increasing nanoparticle branching on the Young's modulus of a common structural elastomer, poly(styrene block−ethylene−butylene block−styrene) (SEBS) (20). We chose SEBS since it is a widely used structural copolymer, has a 40% phase (ethylene−butylene) of similar chemical makeup as our nanoparticle surface ligands (although it is incompatible with 60% of the polymer, the polystyrene (PS) phase), and is amorphous, allowing for improved intercalation with the nanoparticles.…”