Laser-Driven High-Velocity Microparticle Impacts on Polymeric Materials

High-velocity microparticle impact experiments have been applied to a large range of material systems and research fields from micrometeorite impacts to drug delivery to additive manufacturing. In a laser-induced particle impact test (LIPIT), microparticles are accelerated via laser ablation of a metallic absorbing layer on a glass substrate. The ultimate particle velocity is determined by the laser power used for the ablation event. Microparticles can be accelerated from ~50 m/s to ~1500 m/s, depending on particle characteristics (size and density). The particles are imaged before, during and after impact with a Specialised Imaging SIMx ultra-high-speed multi-frame camera that can record up to 16 images with a time resolution as short as 3 ns per frame. These high-speed images are utilized to measure incoming and rebound velocities, and to probe in real-time the deformation, depth of particle penetration and plastic or elastic deformation dynamics. In addition, each impact area can be further characterized post-impact with full knowledge of the kinetics of the impact event.<br/>We discuss the application of LIPIT to study the dynamic mechanical responses of poly(urethane urea) elastomers and two-component polyurethanes. In some cases, a strain rate dependent hardening is observed. Along with the dynamic impact data, we use small and wide angle X-ray scattering (SAXS/WAXS), atomic force microscopy (AFM) and infrared spectroscopy to provide a chemical and bonding picture to explain the impact behavior. In addition, we use broadband dielectric loss spectroscopy (BDS) to probe the mechanical responses of the polymeric materials studied over a wide range of frequencies.