Material Properties of Aerogel Measured using Bow Shock Induced by Supersonic Particle Impact

Aerogels are lightweight materials with a nanoporous structure that captivate the interest of researchers in various fields of science and technology. They possess numerous exceptional characteristics and find applications in a wide range of areas, including thermal and acoustic insulation and kinetic energy absorption. Typically, the mechanical properties of aerogel were measured using uniaxial compression, three-point bending, ultrasonics, and atomic force microscopy. However, accurately measuring the mechanical properties of aerogel can be challenging due to its low density, high porosity, and brittleness. Aerogels, especially silica aerogel, are known to be fragile and brittle. This makes them inapt for load-bearing testing methods.<br/>In this study, we utilize a method called laser-induced particle impact testing (LIPIT) to investigate the properties of aerogel materials. Specifically, we report on the observation of bow shock generation during supersonic particle impacts. It is worth noting that previous works did not report the occurrence of bow shocks, as solid or liquid samples in those studies typically possess higher acoustic speeds compared to projectile speeds. However, aerogel, an air-like material with intricate foam structures, may exhibit a significantly lower acoustic speed (around 100 m/s) than our typical projectile speed (approximately 1000 m/s). This characteristic facilitates the generation of bow shocks. We can accurately extract material properties by performing aerodynamic analysis on bow shocks. The advantage of our bow shock-based study is that it eliminates the risk of altering the material properties before the measurement takes place since the bow shock is the fastest event in the system. Moreover, our approach not only allows for the determination of material properties such as acoustic speed and bulk modulus but also enables the calculation of the previously unreported drag coefficient. Our results have implications for the design of aerogel-based materials for various applications, including impact protection and shock mitigation.