Phenomenological studies of the response of granular and geological media to high - speed ( Mach 1 - 5 ) projectiles

The primary objective is establishing tangible experimental methods and data analyzing methods in order to grasp various phenomena, which were the behavior of ejecta and projectile, the penetration depth and speed of projectile, fractured grains and the pressure distribution, induced by high-speed impact of projectile on sand. The plate impact experiments were conducted using vertical powder gun. The principal results are summarized as follows: Sands around the penetrated projectile were smashed to fine powder of 5 f.ll11 or less like a potato starch. Circumferential crashed sands were conically distributed and generated at impact velocity above 300 m/s. Conical massive crashed sand was produced ahead of projectile and vertical angle converged to around 60" as the velocity increases. The projectile penetrated at a speed about equal to the impact velocity in the initial penetration and decelerated rapidly over since. 1. INTRODUCTON Collisions between geological materials and rigid bodies occur in vanous situations, which are excavation, construction, military application and asteroid impact. Accordingly, the impact and penetration of projectiles in soil have long been studied extensively' 8 However, for geological particulate materials such as sand, because the particle behavior is so complicated due to heterogeneity and instability of granular media, there have been few experiments investigating the impulse loading of these media, and the penetration properties on them are less understood. Dynamics of projectile penetration into sand depends greatly on the features of motion and state of the sand material at the interface with the projectile. The final goal of this study is to develop an understanding of behavior of projectile during penetration, condition and distribution of comminuted sands and pressure distribution in sand under the impulse loading. As the first step, the primary objective is establishing tangible experimental methods and data analyzing methods in order to grasp various phenomena induced by high-speed impact of projectile on sand. 2. EXPERIMENT Plate impact experiments were performed using vertical powder gun as shown in Fig.l. The projectiles with a mass of I 2 or I 2.5 g consisted of a plate impactor of stainless steel or brass 5 mm thick, I 5 mm diameter, mounted on the fi·ont of a polycarbonate sabot as shown in Fig.2. The impact velocities investigated ranged from 150 to I 400 m/s. The target was made up of quartz sands with a grain diameter of between 0. I and I mm and a density of2.65x i0 kg/m. Grain size distribution was shown in Fig.3 , and the grain size using in this experiment was 300500 f.lill. The quartz sands were placed in three kinds of containers (see Fig.4 and Table I ). In the case of conta iner B and C, the packing density was I .49I .56x I 0 kg/m, implying a porosity of 40-43 %. Behavior of the ejecta and the projectile during initial penetration was visualized with high space and time resolutions using high-speed camera (MEMRECAM GX-8, NAC Image Technology Inc.) with 1,000 or 20,000 fps and ultra high-speed camera (ULTRA Cam HS-106E, NAC Image Technology Inc.) with 200,000 fps.