Hypervelocity impact response and protection for the track steels of rocket sled system via light-gas gun experiments

Hypervelocity rocket sled systems are critical for testing advanced military technologies, yet track damage at speeds exceeding Mach 5 remains a significant challenge for system reliability and performance. In this study, we investigated the hypervelocity impact response and protection for high-strength U71Mn or bainitic steel used in rocket sled tracks. Flyer plate impact experiments using a two-stage light-gas gun were conducted to study the hypervelocity collision response, followed by the microstructural characterization via optical microscope, scanning electron microscopy equipped with electron backscatter diffraction to reveal underlying damage mechanisms. Then, the calibrated thermal-mechanical coupled finite element simulations using the Johnson-Cook constitutive model and Mie-Grüneisen equation of state were carried out. Results indicated that bainitic steel exhibits superior impact resistance with predominantly smooth scratch-dominated damage due to its higher ductility. In contrast, U71Mn suffered significant material spallation and crack propagation arising from brittle fracture mechanisms. Zinc-rich epoxy primer coatings effectively mitigated stress concentration and temperature rise in the substrate at impacting velocities below 2.4 km/s, so as to suppress the microstructural damage such as adiabatic shear bands and dynamic recrystallization. However, coating protection diminished at ultra-high-speed impacts due to the coating failure. Dimensional analysis established quantitative relationships of the gouge damage size to projectile mass, impact velocity, and material yield strength. This study provides in-depth insights into damage mechanisms in hypervelocity rail systems, demonstrating that bainitic steel combined with protective coatings can significantly enhance impact resistance and system reliability, offering valuable guidance for the design and optimization of hypervelocity testing platforms.