For the investigation of phenomena occurring when a body hits the surface of another body, which is generally bigger than the first one, the accelerator facilities of Fraunhofer EMI uniquely cover a very broad range of parameters with regard to impact masses and impact velocities. Depending on the task, the appropriate facility can be chosen – or several test facilities can be used complementary for solving a single problem.
Schematic setup of a laboratory accelerator
Fraunhofer EMI investigates impact processes under laboratory conditions. The schematic setup of an accelerator with a highly instrumented impact chamber attached to it is shown in the figure. Observing high-dynamic processes requires very high time resolution. As imaging procedures, flash X-ray technology, high-speed cameras and high-speed video cameras are used. For obtaining especially high impact velocities, two-stage laboratory accelerators are deployed. To this end, the chemical energy of a propellant is exploited in a first stage to compress a gas with very low molecular weight, like hydrogen or helium, by means of a piston running inside a pump tube and to finally build up a pressure of about 10,000 bars within the high-pressure section. In this dynamic process, a membrane bursts and the bottom surface of the projectile gets hit by the incoming flow. As very high flow velocities can be obtained for the light gas, this holds also true for the projectiles which can reach orbital velocities of near-earth satellites in space.
An impact experiment in process
Fraunhofer EMI uses laboratory accelerators to conduct impact experiments under laboratory conditions. By means of single-stage accelerators, velocities of up to three kilometers per second can be reached. Especially for velocities higher than three kilometers per second, Fraunhofer EMI uses two-stage accelerators. The animation shows the first stage of such a facility where the chemical energy of a propellant in the so-called pump tube accelerates a piston in order to put a gas of very low molecular weight, such as hydrogen or helium, under very high pressure. The highest pressure is gained at the end of the piston’s movement, with the piston being stopped by the tapering of the barrel diameter.
At the end of this section, a membrane yields to the built-up pressure and is perforated, and the bottom surface of the projectile which is to be accelerated gets hit by the incoming flow. The animation demonstrates how an aluminum sphere is accelerated this way, how its velocity is determined and how its impact on an inclined target is investigated.
Fraunhofer Institute for High-Speed Dynamics, Ernst-Mach-Institut, EMI