Space debris in Earth's orbit, especially small things that are untraceable and unavoidable, have been a growing concern. Experiments and satellites need to be as light as possible so numerical simulation can be used to enhance or improve the protection structure of the spacecraft, and reduce the harm of the space debris. 

For  the past 20 years, the Laboratory for Shock Wave and Detonation Physics Research in the China Academy of Engineering Physics (CAEP) has conducted research in hypervelocity launch technology.  In their project, they work on optimization of launcher configuration, physical design of the flier plate, material processing and experimental measurement technology, and also the experimental data of equation of state (EOS) for the material under ultra-high pressure.

Their project has led to better hypervelocity launch theory and experiment technology, and the development of the material science and the processing technology as well. The concrete achievements in this project are as follows:

Comparison of the flier velocity between experiment and numerical results is shown. The thickness of titanium flier is 0.5mm, and the impact velocity is 7.587km/s. Credit: ©Science China Press

1. The fluid dynamic codes–the Multi-Fluid Piecewise Parabolic Method (MFPPM) and Level Set Fluid in Cell (LSFC) have been developed, and the optimization of the launcher's configuration and physical design of the flier plate have been carried out by the MFPPM and LSFC codes. 

The code MFPPM, which can be applied to the multi-dimensional and multi-fluid dynamic simulation, has been validated in the simulation of Sandia's hypervelocity launcher, and widely used in the optimization of the hypervelocity launcher and physical design of the flier. However, the MFPPM does not consider the material strength due to its slight effect under the hypervelocity. Luckily, the LSFC proves to be a remedy for this shortcoming.

Evolving but being different from the HELP code, the LSFC takes the Level Set method to describe the material interface. Despite of its only first-order accuracy, the LSFC is able to handle adaptive meshing and parallel computing. Furthermore, it is compatible with various forms of multiphase equation of state, and easily deals with the fluid dynamic simulation including different constitutive models and strength models.

It also can be widely used to numerically simulate the transient dynamics processes such as process driven by detonation, the loading effect and the penetration in the flied of explosion and detonation shock dynamics. In addition, it is suitable for the numerical simulation of impact generated debris and structural protection in the hypervelocity impact process.

2. The DISAR/DPS testing and diagnostic technologies have been developed, and the simultaneous measurement of shock wave velocity and particle velocity has been realized, paving the way for the accurate measurement of EOS data by absolute method. In the previous study, our group has investigated the Hugoniot data of various metal materials under ultra-high loading pressure using the acquired quasi-isentropic loading technology, which provides precious and high-quality experimental data for the relative research in weapon physics.

The continuous successful applications further maturate loading technology of the three-stage light gas gun. In the past two years, we have launched aluminum, tantalum and platinum flier to velocity of 11km/s, 10.0km/s and 9.0km/s, respectively. Moreover, we successfully launch a tantalum flier to impact the platinum target in March 2014,in which the flier was accelerated to 10.4km/s and kept relatively flat, and the loading pressure in platinum target went up to 1060GPa.

This represented another successful launch at ultra-high pressure after the experiment with pressure up to 1018GPa in December 2013, in which the precious EOS data in the platinum target was obtained. Historical breakthroughs have thus been made in the two successful loading experiments performed on three-stage light gas gun with pressure up to 1TPa, and it turns out to be the first record to obtain the pressure with TPa magnitude loading by gas gun under the experiment condition in the world.

Article:"The gas gun launch advances in numerical simulation of hypervelocity impact", SCIENTIA SINICA Physica, Mechanica&Astronomica, 2014, Vol 44(5).Source: Science China Press