Use of SPH and Lagrangian meshing technique to assess damage area in bumper shields impacted by hypervelocity space debris
Space debris are objects in Earth’s orbit consisting of fragments of spent rocket stages, non-functional satellites, and parts like fasteners, paint chips and other waste materials in the lower earth orbits (LEO) (200 – 2000 km/s) traveling at hypervelocity with maximum speeds of 16 km/s. These objects can cause considerable damage to spacecraft structure, the Space Shuttle and the International Space Station which are orbiting around the earth at altitudes of 300 to 500 km/s in the LEO. Damage occurs when the debris traveling at hypervelocity impact (HVI) the spacecraft structure. Hence there is necessity to not only develop spacecraft with good shielding, but also develop a means of spacecraft pressure wall repair. A NASA EPSCoR grant for designing a portable friction stir welder to repair the hypervelocity impact damage caused was the driving force for this thesis topic. A detailed understanding of the extent of damage to the spacecraft shielding system was necessary to understand repair requirements expected for the design of a space-bound Friction Stir Welder. A spacecraft shielding system can consist of a double bumper shielding system placed ahead of the pressure wall. The current goal of this study was to determine the damage area of the pressure wall, using the new grid less Smoothed Particle Hydrodynamics (SPH) meshing techniques and the regular Lagrangian meshing technique. The approach was to model and validate the damage area due to the HVI against existing test data, and to conduct a parametric study for various impactor shapes, velocities and impact scenarios. The software tools used for modeling were PATRAN for the Lagrangian models and LS-Prepost for SPH modeling. The simulation was analyzed in LS-DYNA, a non-linear finite element dynamic analyzer. Simulations were initially conducted using a spherical projectile; later parametric studies were conducted with varied impactor shapes. The materials for the plate and impactor were alloys of Al (6061-T6, l100-O, 2024-T4). It was observed that the model developed using SPH meshing technique generated the debris cloud as in the actual impact scenario, unlike the Lagrangian meshing technique which had problems with mesh tangles. Hence the SPH technique provided a potential means of predicting pressure wall damage due to HVI.