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. In this work, we study the mechanical behavior of polymer gels subjected to high-velocity microparticle impact, with strain rates up to 107 s−1, through direct visualization of the impact dynamics. In an all-optical laser-induced 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 multi-frame camera with nanosecond time resolution. 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. 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 imaging performed with high temporal and spatial resolution can serve as direct input for simulations of high-velocity impact responses and high strain rate deformation in gels and other soft materials.

中文翻译：

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粘弹性凝胶在高速微粒冲击下的高应变率行为

冲击实验通常在宏观尺度上进行，长期以来一直用于研究材料的机械性能。与弹道药物输送等应用相关的微尺度高速撞击在单个撞击事件的水平上仍未得到充分探索。在这项工作中，我们通过冲击动力学的直接可视化研究了聚合物凝胶在高速微粒冲击下的力学行为，应变率高达 107 s-1。在全光学激光诱导粒子冲击试验中，直径为 10-24 μm 的钢微粒通过激光烧蚀过程加速到 50 到 1000 m/s 的速度。使用具有纳秒时间分辨率的高速多帧相机监控撞击事件。我们测量微粒轨迹并提取一系列粒径、速度和凝胶浓度的最大和最终穿透深度。我们提出了一个改进的 Clift-Gauvin 模型，并证明它充分描述了单个轨迹和穿透深度。模型参数，即表观粘度和抗冲击性，是针对一系列聚合物浓度提取的。激光诱导微粒冲击试验可以对凝胶上的单粒子冲击动力学进行可重复的测量，并为理解这些动力学提供定量基础。我们表明，修正的 Clift-Gauvin 模型考虑了阻力系数的速度依赖性，与更常用的 Poncelet 模型相比，它与实验数据的一致性更好。