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

Abstract

A ballistic parameter that influences the ballistic performances of a high-performance yarn is the critical velocity. The critical velocity is defined as the projectile striking velocity that causes instantaneous rupture of the yarn upon impact. In this study, we performed ballistic experiments to determine the critical velocity of a Twaron® yarn transversely impacted by a razor blade. A high-speed camera was integrated into the experimental apparatus to capture the in-situ deformation of the yarn. The experimental critical velocity demonstrated a reduction compared to the critical velocity predicted by the classical theory. The high-speed images revealed the yarn specimen failed from the projectile side toward the free end when impacted by the razor blade. To improve the prediction capability, the Euler–Bernoulli beam and Hertzian contact models were used to predict the critical velocity. For the Euler–Bernoulli beam model, the critical velocity was obtained by assuming the specimen ruptured instantaneously when the maximum flexural strain reached the ultimate tensile strain of the yarn upon impact. On the other hand, for the Hertzian contact model, the yarn was assumed to fail when the indentation depth was equivalent to the diameter of the yarn. The errors between the average critical velocities determined from experiments and the predicted critical velocities were around 19% and 48% for the Euler–Bernoulli beam model and Hertzian contact model, respectively.

The Effect of Projectile Nose Shape on the Critical Velocity of High-Performance Yarn

“…It is important to emphasize that for a given case, the critical velocity has a range. If the impact of the projectile on the yarn was below the lower limit of the critical velocity, the transverse waves would develop and propagate in the yarn, causing it to deform according to Smith theory [3,6]. On the other hand, if impacted above the upper limit, the yarn would rupture instantaneously [2,6].…”

“…If the impact of the projectile on the yarn was below the lower limit of the critical velocity, the transverse waves would develop and propagate in the yarn, causing it to deform according to Smith theory [3,6]. On the other hand, if impacted above the upper limit, the yarn would rupture instantaneously [2,6]. When impacted within the range of the critical velocity, some of the fibers would rupture upon impact and the remaining fibers would deform into a triangular shape as describe by Smith theory [2,3,6].…”

“…On the other hand, if impacted above the upper limit, the yarn would rupture instantaneously [2,6]. When impacted within the range of the critical velocity, some of the fibers would rupture upon impact and the remaining fibers would deform into a triangular shape as describe by Smith theory [2,3,6]. Therefore, when a yarn is transversely impacted by a projectile, the initial deformation of the yarn falls into one of the three possible cases: (i) no rupture, (ii) partial rupture, and (iii) instantaneous rupture [2,6].…”

“…A gas/powder gun setup was utilized to perform the ballistic experiments to determine the critical velocity of the yarn, as shown in Figure 1. The detail of the experimental setup, including the method to attach the yarn, was presented in previous studies [6,12]. The load cells were mounted to the grips to measure the load history.…”

“…Such transverse speed can be determined analytically using the projectile's striking velocity and the axial mechanical properties of the yarn [3][4][5]. On the other hand, if the projectile strikes above the critical velocity, the transverse displacement of the yarn is insignificant [2,6]. Additionally, even though the Smith theory is capable of predicting the critical velocity, the predicted results are always overestimated compared to those obtained from experiments [2,[6][7][8].…”