Structure and defects in high-performance aramid fibers
type: CreativeWork
description: High performance aramid fibers, such as Kevlar, AuTx, and Twaron have been designed for ultra-high specific strength and stiffness. These fibers derive their superior properties from the high degree of molecular orientation that allows for efficient load transfer to the backbone covalent bond axis. While the experimental Young’s modulus of aramid fibers approaches the theoretical limits, the measured mechanical strength is quite lower than the predicted values. The objective of this dissertation research was to obtain an understanding of the subtle differences in the structure of commercial grade aramid fibers with different tensile strength and modulus values. Towards this goal, single fiber tension experiments were conducted with various fiber gauge lengths to evaluate the existence of fiber length size effects and, therefore, a statistical distribution of defects limiting the fiber strength. The test results were supported by several studies of the fiber structure via various modalities of high resolution microscopy. Uniaxial tension tests were carried out with AuTx and KM2 fibers with gauge lengths between 100 µm and 10 mm. The average strength of KM2 fibers was 4.4 ± 0.4 GPa, with a high value of 5.2 GPa and a low value of 3.5 GPa. The average tensile strength decreased by 20% as the gauge length increased from 100 µm to 10 mm. The tensile modulus of KM2 fibers was calculated to be 85.6 ± 3.7 GPa. Similarly, the average strength of AuTx fibers was 5.5 ± 0.7 GPa, with a high value of 6.8 GPa and a low value of 4.4 GPa. A reduction of approximately 20% in the average tensile strength value was also established when the gauge length increased from 100 µm to 10 mm. The relative insensitivity of the fiber tensile strength to the gauge length suggests that failure in both kinds of aramid fibers could be due to processes or defects at length scales well below the micron-scale. High resolution SEM images were obtained to understand the surface morphology and the intern…
abstract: High performance aramid fibers, such as Kevlar, AuTx, and Twaron have been designed for ultra-high specific strength and stiffness. These fibers derive their superior properties from the high degree of molecular orientation that allows for efficient load transfer to the backbone covalent bond axis. While the experimental Young’s modulus of aramid fibers approaches the theoretical limits, the measured mechanical strength is quite lower than the predicted values. The objective of this dissertation research was to obtain an understanding of the subtle differences in the structure of commercial grade aramid fibers with different tensile strength and modulus values. Towards this goal, single fiber tension experiments were conducted with various fiber gauge lengths to evaluate the existence of fiber length size effects and, therefore, a statistical distribution of defects limiting the fiber strength. The test results were supported by several studies of the fiber structure via various modalities of high resolution microscopy. Uniaxial tension tests were carried out with AuTx and KM2 fibers with gauge lengths between 100 µm and 10 mm. The average strength of KM2 fibers was 4.4 ± 0.4 GPa, with a high value of 5.2 GPa and a low value of 3.5 GPa. The average tensile strength decreased by 20% as the gauge length increased from 100 µm to 10 mm. The tensile modulus of KM2 fibers was calculated to be 85.6 ± 3.7 GPa. Similarly, the average strength of AuTx fibers was 5.5 ± 0.7 GPa, with a high value of 6.8 GPa and a low value of 4.4 GPa. A reduction of approximately 20% in the average tensile strength value was also established when the gauge length increased from 100 µm to 10 mm. The relative insensitivity of the fiber tensile strength to the gauge length suggests that failure in both kinds of aramid fibers could be due to processes or defects at length scales well below the micron-scale. High resolution SEM images were obtained to understand the surface morphology and the intern…
author: Clawson, Jan
language: en
keywords: kevlar, aramid, high-performance fiber, AuTx, polymer, liquid crystal
date published: 2014-01-16T18:25:20Z
date modified: 2026-07-22T22:25:38Z
provider: University of Illinois - Urbana-Champaign
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: University of Illinois at Urbana-Champaign

PropertyValue
property ID: Handle
value: http://hdl.handle.net/2142/46888