The effect of particle strength on the ballistic resistance of shear thickening fluids

Abstract

The response of shear thickening fluids (STFs) under ballistic impact has received considerable attention due to its field-responsive nature. While efforts have primarily focused on traditional ballistic fabrics impregnated with these fluids, the response of pure STFs to penetration has received limited attention. In the present study, the ballistic response of particle-based STFs is investigated and the effects of fluid density and particle strength on ballistic performance are isolated. It is shown that the loss of ballistic resistance in the STFs at higher impact velocities is governed by the material strength of the particles in suspension. The results illustrate the range of velocities over which these STFs may provide effective armor solutions.The integration of shear thickening fluids (STFs) in armor systems, a concept reported as early as Gates, 1 has received considerable interest with the recent efforts to embed STFs within ballistic fabrics, 2-5 which has been shown to increase their ballistic performance; however, experimental evidence also suggests performance limitations of these hybrid armour systems. This loss of performance is evident when considering steelcore projectiles 1,5 particularly when multiple layers and higher impact velocities are considered. 3 Park et al. 5 discussed preliminary experimental results in which a loss of effectiveness was seen against steel projectiles (FSPs) above an impact velocity of 300 m/s, the same velocity range investigated by Tan et al. 3 The coupled nature of the fluid-fabric interactions make it difficult to ascertain whether this behavior is due to a loss of performance within the STF itself or a transition in the dominant failure mode within the fibers, rendering the presence of the STF inconsequential to the ballistic response. In the present study, we investigate the ballistic penetration of several STFs, particularly focusing on the role of particle strength in determining the ballistic response of STFs through variations of the particle material and volume fraction in the suspensions.STFs are field-responsive fluids which can undergo a sudden fluid-solid transition under certain stimuli. STFs have been extensively characterized using low-stress dynamic techniques, 6-8 in which liquids are considered incompressible. These conditions are not directly relevant to the dynamic high-stress environment of a ballistic impact, where compressibility effects dominate material responses. 9 Lee and Kim 14 estimated the stagnation pressure at the nose of a steel projectile impacting a STF-impregnated fabric to be on the order of several gigapascals, stresses at which compressibility effects must be considered. Under ballistic conditions, in addition to traditional shear thickening mechanisms, a compressioninduced clustering of particles should be expected as the a) oren.petel@mail.mcgill.ca liquid density and particle volume fraction increase under high pressures, 10-13 resulting in extensive particle force chains forming around the projectile (Fig. 1a and 1b) as the...

The rheology of shear thickening fluids with various ceramic particle additives

“…Unlike silica, the additives do not contribute to the thickening mechanism because they are not constitutive particles for the STFs. According to Petel et al [35], [36], suspensions of ethylene glycol and SiC particles exhibit shear thinning behavior rather than thickening. For this reason, and the findings will be described in further paragraphs, additive particles negatively influence the thickening behavior of STFs.…”

“…It was noted that MRSTFs have features of both fluids, but they are more like MR fluids. As well as the magnetic particles in STFs, Petel et al [35], [36] investigated the ballistic resistance of bulk STFs, including carbide particles. According to their studies, carbide particles change the thickening behavior of the STFs while improving its ballistic resistance by increasing the density of this suspension and the dynamic material strength of the fluids.…”

Estimating the resistive strength of dense particle suspensions during ballistic penetration

“…Since the response of these particle-based suspensions are strongly dependent on the stress state within the fluid [7], it should be expected that the multi-dimensional stress state of a ballistic impact would not result in the same level of interparticle stress transfer seen in the plate impact experiments [8]. Evidence from ballistic experiments has demonstrated that the particle material choice strongly influences performance [4,5,9]. In fact, the study by Kalman et al has shown that Kevlar fabrics embedded with dry silica particles outperform fabrics embedded with a silicabased STF [9].…”

“…Despite the suggested protective applications for these particle-based STFs, the strength limitations of these fluids at high strain rates have received little attention. In the present study, an estimate of the effective dynamic strength of a silica-based STF is investigated from available ballistic penetration data [4,5].…”

Comparison of rheological behaviors with fumed silica-based shear thickening fluids

“…Another unique aspect is the reversibility of this effect as the STFs will return to fluid state once the shear force is removed or reversed, making it advantageous as a reusable product in applications. Current applications with STFs include scenarios which require energy adsorption from sharp projectiles such as knife or spike attacks [1][2][3][4][5][6][7][8][9][10][11], acoustic and mechanical vibrational dampening control [12,13] and in a passive capacity in other polymeric materials [14][15][16]. The theory of shear thickening includes an order-disorder transition of particles [17,18] and formation of clusters, otherwise known as "hydroclusters" [19][20][21][22] that only form once the applied shear forces overcome particle repulsion forces.…”