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In this study, ballistic experiments were performed to determine the critical velocity of a Twaron® 2040 high-performance yarn transversely impacted by round projectiles. Four different round projectiles possessing a radius of curvature of 2 µm, 20 µm, 200 µm and 2 mm were used in this study. Load cells were mounted to the grips to measure the load history of the yarn upon impact. A high-speed camera was incorporated into the ballistic experimental setup to capture the failure process of the yarn upon impact. A scanning electron microscope was utilized to perform post-mortem failure analysis on the recovered specimens. The results showed that as the radius of curvature of the projectile increased, the critical velocity also increased. The critical velocities for all cases were bounded between those predicted from the Euler–Bernoulli beam and Smith models. Upon impact above the upper limit of the critical velocity, the axial loads revealed a demonstrative reduction. The failure surfaces changed from shear to fibrillation as the radius of curvature increased. For those specimens that failed in shear, Hertzian contact model was used to predict the critical velocity.
Boon Him Lim; Jou-Mei Chu; Jinling Gao; Benjamin Claus; Yizhou Nie; Wayne Chen. The Effect of Projectile Nose Shape on the Critical Velocity of High-Performance Yarn. Fibers 2019, 7, 29 .
AMA StyleBoon Him Lim, Jou-Mei Chu, Jinling Gao, Benjamin Claus, Yizhou Nie, Wayne Chen. The Effect of Projectile Nose Shape on the Critical Velocity of High-Performance Yarn. Fibers. 2019; 7 (4):29.
Chicago/Turabian StyleBoon Him Lim; Jou-Mei Chu; Jinling Gao; Benjamin Claus; Yizhou Nie; Wayne Chen. 2019. "The Effect of Projectile Nose Shape on the Critical Velocity of High-Performance Yarn." Fibers 7, no. 4: 29.
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.
Boon Him Lim; Jou-Mei Chu; Benjamin Claus; Yizhou Nie; Wayne Chen. Critical Velocity of High-Performance Yarn Transversely Impacted by Razor Blade. Fibers 2018, 6, 95 .
AMA StyleBoon Him Lim, Jou-Mei Chu, Benjamin Claus, Yizhou Nie, Wayne Chen. Critical Velocity of High-Performance Yarn Transversely Impacted by Razor Blade. Fibers. 2018; 6 (4):95.
Chicago/Turabian StyleBoon Him Lim; Jou-Mei Chu; Benjamin Claus; Yizhou Nie; Wayne Chen. 2018. "Critical Velocity of High-Performance Yarn Transversely Impacted by Razor Blade." Fibers 6, no. 4: 95.
In a previous paper, we presented a scaling law for the ballistic-limit velocity for the 7.62 mm APM2 bullet and five aluminum alloy plates. This scaling law predicts that the ballistic-limit velocity is proportional to the square root of the product of the plate thickness and a material strength term. In this note, we show that this same scaling law can be used to accurately predict ballistic-limit velocity for the larger 12.7 mm APM2 bullet.
M. J. Forrestal; B. Lim; W. Chen. A Scaling Law for APM2 Bullets and Aluminum Armor Plates. Experimental Mechanics 2018, 59, 121 -123.
AMA StyleM. J. Forrestal, B. Lim, W. Chen. A Scaling Law for APM2 Bullets and Aluminum Armor Plates. Experimental Mechanics. 2018; 59 (1):121-123.
Chicago/Turabian StyleM. J. Forrestal; B. Lim; W. Chen. 2018. "A Scaling Law for APM2 Bullets and Aluminum Armor Plates." Experimental Mechanics 59, no. 1: 121-123.
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.
Boon Him Lim; Jou-Mei Chu; Wayne Chen. Mechanical Behavior of High-Performance Yarns Transversely Loaded by Different Indenters. Fibers 2018, 6, 69 .
AMA StyleBoon Him Lim, Jou-Mei Chu, Wayne Chen. Mechanical Behavior of High-Performance Yarns Transversely Loaded by Different Indenters. Fibers. 2018; 6 (4):69.
Chicago/Turabian StyleBoon Him Lim; Jou-Mei Chu; Wayne Chen. 2018. "Mechanical Behavior of High-Performance Yarns Transversely Loaded by Different Indenters." Fibers 6, no. 4: 69.