Photonic doppler velocimetry for study of rapid penetration into sand

Quantitative description of the interaction of high-speed projectiles with soils is important for many engineering applications, and provides insights into high strain rate constitutive behavior. In this paper, a novel method known as photonic Doppler velocimetry (PDV), capable of producing time resolved velocity measurements, is adapted for the study of objects penetrating rapidly into sand. Fundamentals of PDV are described, and the applicability of the method is demonstrated by producing time-resolved velocity measurements of spherical projectiles penetrating Ottawa sand models at high velocities in the range of 300 m/s. Penetration tests demonstrate that PDV is capable of producing velocity measurements even after the penetrator has reached a depth well below the soil surface. Results of the tests confirmed that resistance to penetration increases as relative density of the sand deposit increases. Moreover, there appears to be a threshold penetration velocity in dense dry sand, below which resistance to penetration reduces considerably. A quantitative description of deceleration of penetrators in soils can be adequately provided for most of the penetration using a simple drag force model.