High-Strain-Rate Behavior of a Viscoelastic Gel Under High-Velocity Microparticle Impact

Abstract

Background: Impact experiments, routinely performed at the macroscale, have long been used to study mechanical properties of materials. Microscale high-velocity impact, relevant to applications such as ballistic drug delivery has remained largely unexplored at the level of a single impact event. Objective: In this work, we study the mechanical behavior of polymer gels subjected to high-velocity microparticle impact, with strain rates up to 10 7 s -1 , through direct visualization of the impact dynamics. Methods: In an all-optical laserinduced particle impact test, 10-24 μm diameter steel microparticles are accelerated through a laser ablation process to velocities ranging from 50 to 1000 m/s. Impact events are monitored using a high-speed multiframe camera with nanosecond time resolution. Results: We measure microparticle trajectories and extract both maximum and final penetration depths for a range of particle sizes, velocities, and gel concentrations. We propose a modified Clift-Gauvin model and demonstrate that it adequately describes both individual trajectories and penetration depths. The model parameters, namely, the apparent viscosity and impact resistance, are extracted for a range of polymer concentrations. Conclusions: Laser-induced microparticle impact test makes it possible to perform reproducible measurements of the single particle impact dynamics on gels and provides a quantitative basis for understanding these dynamics. We show that the modified Clift-Gauvin model, which accounts for the velocity dependence of the drag coefficient, offers a better agreement with the experimental data than the more commonly-used Poncelet model. Microscale ballistic impact

High-velocity micro-projectile impact testing

“…Recent experiments by Veysset et al allowed the development of a refined model for particle impact in yield-stress fluids at intermediate Reynolds number (Fig. 10d) (141). In all gels tested, it was shown that, under micro-scale testing, the resistance to penetration, related to materials strength, significantly increased compared to macroscale experiments by orders of magnitude, evidencing rate strengthening effects.…”

“…Other soft materials beyond polymers, such as gels or biomaterials, have also been tested with LIPIT to determine their rate-dependent properties. Notably gelatin and synthetic gels, including poly(styrene-bethylene-co-butylene-b-ethylene) (SEBS) polymer-based gels with non-aqueous solvent, with varying concentrations were investigated (140,141). Particle trajectories were observed in the transparent specimen (Fig.…”

The Projectile Perforation Resistance of Materials: Scaling the Impact Resistance of Thin Films to Macroscale Materials

“…The Poncelet model was previously applied to LIPIT studies to predict the penetration depth, δ t , into thick polymer gels. 22 However, we are interested in a slightly different problem: the conditions of the impact test and the materials properties that determine the onset of complete penetration through a film of finite dimensions.…”

Modeling high strain-rate microcavitation in soft materials: the role of material behavior in bubble dynamics

“…To address this challenge, significant effort in recent years has gone towards developing new characterization techniques capable of extracting information on the high strain-rate mechanical behavior of soft materials -including small-scale ballistic cavitation, 18 laser-induced particle impact testing, 19 shear impact testing, 20 and Inertial Microcavitation Rheometry (IMR), [21][22][23][24][25] which is the focus of the present work. IMR belongs to a class of cavitation-based material characterization techniques 26 -including needle-induced cavitation 11,12,18 and volume-controlled cavity expansion [13][14][15] -and is unique in its ability to mechanically characterize soft materials at high strain rates greater than 10 3 s À1 .…”