Modeling of Fabric Impact With High Speed Imaging and Nickel-Chromium Wires Validation

Abstract

Ballistic tests were performed on single-yarn, single-layer and ten-layer targets of Kevlar® KM2 (600 and 850 denier), Dyneema® SK-65 and PBO® (500 denier). The objective was to develop data for validation of numerical models so, multiple diagnostic techniques were used: (1) ultra-high speed photography, (2) high-speed video and (3) nickel-chromium wire technique. These techniques allowed thorough validation of the numerical models through five different paths. The first validation set was at the yarn level, where the transverse wave propagation obtained with analytical and numerical simulations was compared to that obtained in the experiments. The second validation path was at the single-layer level: the propagation of the pyramidal wave observed with the high speed camera was compared to the numerical simulations. The third validation consisted of comparing, for the targets with ten layers, the pyramid apex and diagonal positions from tests and simulations. The fourth validation, which is probably the most relevant, consisted of comparing the numerical and experimental ballistic limits. Finally for the fifth validation set, nickel-chromium wires were used to record electronically the waves propagating in the fabrics. It is shown that for the three materials the waves recorded during the tests match well the waves predicted by the numerical model.

Modeling and Experiments on Ballistic Impact into UHMWPE Yarns Using Flat and Saddle-Nosed Projectiles

“…Chocron et al [30] have reported data from yarn shooting experiments involving 0.3 caliber, FSP projectiles impacting Kevlar ® S5705, Dyneema ® SK65 and Zylon ® PBO yarns. For a range of incremental impact velocities, it was determined whether or not yarns fail immediately by evaluating frames from high speed video.…”

Exploration of Wave Development during Yarn Transverse Impact

“…In order to circumvent this high variability measurement, a more appropriate method has been pursued wherein one tracks the difference in longitudinal wave travel times from projectile-yarn contact site to the detection of the longitudinal wave from the clamping load cells for drastically different yarn lengths L 1 and L 2 ; L 1 and L 2 are measured as 10.3 cm and 73.2 cm, respectively. Such a measurement is described in Equation (10) and is demonstrated in Figure 3. As previously stated, possessing accurate L 1 and L 2 is achieved using a laser bore site, allowing for Equation (10) to provide an accurate estimate of the wave speed of the yarn material.…”

“…Such a measurement is described in Equation (10) and is demonstrated in Figure 3. As previously stated, possessing accurate L 1 and L 2 is achieved using a laser bore site, allowing for Equation (10) to provide an accurate estimate of the wave speed of the yarn material. As an aside, it is important to note that the longitudinal stress wave must also travel through the yarn clamping fixtures, but accounting for this travel time is unnecessary if identical clamping fixtures are used on both ends of the yarn; the longitudinal wave travel time through the clamps is identical in both fixtures and is inherently subtracted out using the aforementioned time difference method.…”

“…Although a rather uncommon experiment, transverse impact into single yarns has been historically used to determine baseline yarn mechanical properties, specifically to determine yarn stiffness in the longitudinal direction and the yarn critical velocity, wherein the material fails "instantly" upon projectile-yarn contact [1][2][3][4][5][6][7][8][9][10]. Such an understanding of stiffness and critical velocity is used to assess the efficacy of implementing a specific yarn material into a full body armor system; an efficacy analysis is most reasonably performed by determining the Cunniff parameter (Ω 1/3 ) [11], which is described in Equation (1),…”

“…The reader is specifically directed to work performed by Chocron et al [10] and Chocron and Walker [13], who take great effort in determining the critical velocity for several types of high-performance yarn. Additionally, Walker and Chocron [13] present a strong explanation for the oft-quoted difference between experimental and theoretical critical velocities predicted by Equations (2)- (6).…”