Mechanics of hypervelocity simultaneously launched distributed particles

Abstract

Understanding the complex physics of micrometeoroid/orbital debris (MMOD) cluster impacts to spacecraft structures and particulate impacts such as dust, ice, rain, etc. to hypersonic vehicles is essential to ensure safe space travel and hypersonic flight. Hypervelocity impacts resulting from simultaneously launched distributed particles (SLDPs) can be used to realistically replicate such environments. A method to controllably launch and perform in-situ characterization of SLDPs has been developed and implemented. A powder-driven, 12.7 mm smooth-bore two-stage light gas gun was used to launch collections of 0.79 mm and 1.98 mm diameter 2017-T4 aluminum particles to group velocities ranging from 2.4–5.4 km/s. Ultra-high-speed images recorded at 1 MHz were processed using custom-developed two-dimensional digital particle tracking algorithms to characterize the airborne SLDP clusters. In addition, the three-dimensional (3D) features of the SLDP clusters were quantified using impacts to 1.59 mm thick 6061-T6 aluminum plates. Target damage and interactions between adjacent particle impact sites were studied using a combination of numerical simulations and post-impact forensic analyses. Characteristic Elastic Plastic Impact Computation code simulations were used to estimate critical nearest neighbor distances between impact sites below which damage interactions occur and to subsequently probe plastic damage coalescence. For a given particle diameter, the critical nearest neighbor distance was roughly twice the in-plane radial distance from the impact axis to the location of 1% equivalent plastic strain. The plate-thickness-to-particle-diameter ratio was found to affect the plastic strain field more than the crater/perforation size. The predicted crater geometry agreed well with 3D optical profilometry measurements of target impact sites. The approach developed in this work can be readily applied to other particle/target geometries, materials, and impact scenarios, including MMOD cluster impacts and environmental effects on hypersonic vehicles.