Reverse Ballistic Equation of State for a Quenched and Tempered Low Carbon Steel

The objective of this experimental series was to determine the shock Hugoniot of Rolled Homogeneous Armor (RHA) steel, specifically MIL-DTL 12560, which meets the United States Department of Defense specifications. RHA steels are crucial in military vehicles and personnel armor, frequently subjected to dynamic loading from ballistic impacts, explosive shock waves, and shaped charge jets. Understanding their performance and failure mechanisms under such conditions is paramount for ensuring the safety of individuals relying upon this material for protection.

Three reverse ballistic experiments were conducted at Sandia National Laboratories' Shock Thermodynamic Applied Research (STAR) facility using a 4" bore single-stage dual-diaphragm Light Gas Gun (LGG). Photonic Doppler Velocimetry (PDV) served as the primary data acquisition method. The RHA steel, mounted as a flyer on a sabot, impacted targets comprised of nine "standard" materials, yielding twenty-seven shock Hugoniot points across the three shots.

The target samples, measuring 12 mm in diameter and 2 mm in thickness, allowed for normal loading relative to the shock direction before radial release, ensuring uniaxial strain conditions during Hugoniot plateau measurements. This experimental setup enabled the charting of a significant portion of RHA's thermodynamic state space from 0-19 GPa, including the observation of an α to ε phase transition in the iron substrate around 13 GPa.

The resulting shock Hugoniot line, representing the locus of achieved thermodynamic states, provides valuable insights into RHA's behavior under extreme conditions. Future experiments are planned to explore spallation effects with varying temperature, strain rate, and phase changes. Further reverse ballistic and spallation experiments are desired to enhance the accuracy and resolution of the Shock Hugoniot data of material.