Mechanical Behavior of High-Performance Yarns Transversely Loaded by Different Indenters

Abstract

In this study, we performed off-axis transverse loading experiments to study the stress concentration developed in a high-performance yarn with different indenters. A universal testing machine was utilized to perform quasi-static transverse loading experiments on Twaron® yarns. Seven different round indenters possessing radius of curvature ranging from 0.20 to 4.50 mm were employed in the experiments. In addition, post-mortem failure analysis was performed on the recovered specimens via a scanning electron microscope. From the transverse loading experiments, the results showed that, as the radius of curvature of the indenters increased, the concentrated load decreased, causing the failure surfaces to change from a combination of kink band, snapped-back, and localized shear to only fibrillations. The concentrated stresses were predicted by a strain energy model when loaded by an indenter with a radius of curvature smaller than 1.59 mm. For indenters larger than 1.59 mm, the specimens failed in fibrillation, the concentrated stresses agreed well with the stresses predicted by quasi-static circular curved beam theory.

Critical Velocity of High-Performance Yarn Transversely Impacted by Razor Blade

“…A possible reason for the Smith theory to overestimate the critical velocity is that the theory assumes bending is negligible [9,10,12]. Later in the results section, we showed that when the yarn was impacted by a razor blade above the critical velocity, the yarn deflection was small prior to rupture.…”

“…The yarn specimens used in this study were strands of Twaron ® 2040 yarns extracted from plain weave single ply CT 709 Twaron ® in the warp direction. The quasi-static mechanical properties of this yarn were determined in previous studies and are tabulated in Table 1 [12,13]. Table 1.…”

“…Mechanical properties of Twaron ® 2040 yarn and the razor blade. The mechanical properties of Twaron ® 2040 were adapted from [12][13][14].…”

“…A common issue in the Smith model [1] and the Euler-Bernoulli beam model is that the critical velocity only depends on the mechanical properties of the yarn. However, experimental results revealed that the critical velocity was highly dependent on the projectile nose shape [2,12]. As the projectile radius of curvature decreased, the critical velocity also decreased [2].…”

“…The gun barrel possessed an inner diameter of 20 mm and a length of 2.1 m. Figure 1b presents the schematic inside the yarn chamber, which included a pair of lasers and photodiodes to measure the projectile striking velocity. The method of attaching the yarn specimens to the grips was presented in [12] with the exception that the grips were mounted vertically instead of at 45 degrees. The Twaron ® 2040 warp yarns possessed a gage length of 190 mm.…”