Dynamic strength, particle deformation, and fracture within fluids with impact-activated microstructures

Abstract

The evolution of material strength within several dense particle suspensions impacted by a projectile is investigated and shown to be strongly dependent on the particle material in suspension. For stronger particles, such as silicon carbide, the shear strength of the fluid is shown to increase with the ballistic impact strength. For weaker particles, such as silica, the shear strength of the suspension is found to be independent of impact strength in this dynamic range of tests. A soft-capture technique is employed to collect ejecta samples of a silica-based shear thickening fluid, following a ballistic impact and penetration event. Ejecta samples that were collected from impacts at three different velocities are observed and compared to the benchmark particles using a Scanning Electron Microscope. The images show evidence of fractured and deformed silica particles recovered among the nominally 1 μm diameter monodisperse spheres. There is also evidence of particle fragments that appear to be the result of interparticle grinding. The trends observed in the shear strength estimates are interpreted with regards to the particle damage seen in the ejecta recovery experiments to develop a concept of the impact response of these fluids. The results suggest that particle slip through deformation is likely the dominant factor in limiting the transient impact strength of these fluids. Particularly, particle strength is important in the formation and collapse of dynamically jammed particle contact networks in the penetration process.

The Ballistic Response of Particle-Filled Elastomeric Systems

“…Ballistic studies concerning the penetration response of DPS [112,44,113] were sum- present. An expression for the resistive shear stress was derived as an attempt to quantify the dynamic material strength while disregarding the dominating contribution from inertia.…”

“…Although Eq. 32 measures deviations from the inertial (hydrodynamic) response of a suspension, it does not provide much information concerning variations in resisting shear stress exerted by the target at different impact velocities [113]. The work done during penetration (W s ) was derived from the conservation of energy expression proposed by Recht and Ipson [97] (Eq.…”

“…The work done during penetration (W s ) was derived from the conservation of energy expression proposed by Recht and Ipson [97] (Eq. 20), resulting in the expression below [113] W s = M p 2…”

“…where P p is the perimeter of the flat portion of the projectile nose. The expression above was used to calculate the average resistive shear stress of several suspensions penetrated by chisel-nosed projectiles [113], which resulted in Fig. 34.…”

“…As long as interparticle contact does not dominate the response, the particles can be assumed rigid. The defeat mechanisms available for such a composite are matrix cracking or filler-matrix interface failure, whereas particle breakage would only be expected if force chains were formed within the system [113]. Strong particle-matrix adhesion promotes a more uniform stress distribution within the system since the particles are capable of carrying stress without debonding from the matrix.…”