ABSTRACT:In this paper, we present a numerical method to simulate the hypervelocity launcher (HVL) experiment in which the two-stage light-gas gun impact launches flyers to hypervelocity. HVL is a complex process in numerical simulation, which includes multi-materials, multi-interfaces, huge distortion, high densities and severe shock wave problems, etc. A two-step Euler high-resolution finite volume scheme is used to solve the multi-fluid hydrodynamic equations. The first step is the Lagrange step in which the computation cells are distorted to follow the material motion, and the second step is the Remap step where the distorted cells are mapped back to the Euler meshes. Based on the Volume of Fluids model (VOF) and parabolic piecewise method (PPM), a shock wave physics code named multi-fluid parabolic piecewise method (MFPPM) is developed to simulate the experimental configuration of the hypervelocity launchers and the resolution of the algorithm is also tested. We emphasize the distinguished features of the code that aid in understanding the sensitivity of hypervelocity launcher calculations to the numerical methodology. The MFPPM code is verified and validated by simulating a series of hypervelocity launcher experiments implemented in Sandia National Laboratories. Good agreements are shown when comparing the numerical results with experimental data. Besides, in our National Key Laboratory for Shock Wave and Detonation Physics Research, two new models of the high/low density (Tantalum / Titanium) flyer plates HVL experiment are simulated by the code. Again, the numerical results and experimental data agree well with each other.

This article deduced a theoretical method to obtain the second order partial der ivatice of shear modulus with respect to pressure G″P from the theor y of electron structure for crystal materials.We obtained G″P0=-0.033GPa-1 for 93 tungsten alloy,and applied this result in the fini te strain theory of Birch-Murnaghan,when comparing the calculated results of G″ P0=-0.033GPa-1 with the results of G″P=0, we find the results of G″P=0 are greater than that of the results o f G″P≠0.The difference between them becomes greater when the pressu re increases. Therefore,we can conclude that G″P cannot be neglected at high pressures.

In the experimental researches of spacecraft shield structure, it is necessary to launch metal flyers with mass of gram-order to hypervelocity about 10 km/s. Researchers in Institute of Fluid Physics of CAEP have already made a breakthrough of this key technique on the two-stage light gas gun facility. Under laboratory conditions, a LY12 aluminum flyer with mass of gram-order can be driven and accelerated to 11.0 km/s, and Ta and Pt metal flyers with same mass magnitude and higher densities to 10.0 km/s and 9.0 km/s, respectively. Further development on experimental techniques to drive flyers to even higher velocity is expected. In this paper, numerical simulations based on MFPPM code with high order scheme for the process of driving flyers to hypervelocity through gas gun facility are performed. The calculation result of velocity profile of the flyer free surface agrees well with experimental data measured through DISAR. To simulate melting, gasification, plasma changing and other phenomena appearing in hypervelocity impacts, the elastic-plastic hydrodynamics code LSFC in Eulerian frame with independent intellectual property is also developed. Primary numerical simulation for the same problem is carried out. The results of two codes are in excellent agreement. In future work, LSFC code will be further developed to carry out numerical simulation analysis for hypervelocity impacts of space debris and design of shield structures. hypervelocity flyer, hypervelocity impacts, light gas gun facility, MFPPM, LSFC

This article describes a method which combines the static pressure experiment,dynamic experiment and theoretical calculation to obtain the parameters in the SCG constitutive model for tungsten alloy under high pressures. By using the constitutive model we obtained in numerical simulation that the calculated profiles of particle velocity are in accordance with the experimental results. We also conducted some other simulations by using different constitutive models and compared them with experimental results. The results show that the constitutive model we obtained was the best.

This article put forward a method to calculate the temperature coefficient for shear modulus(G′T) by means of theoreticial calculation and dynamic experiments. Firstly,introduce a calculation data G(PS), then combine with dynamic experimental data G(PH) to obtain G′T. Taking tungsten alloy as an example, the results show that G′T varies with pressure and temperature at the beginning, but at high pressure and high temperature, it is almost a constant of -004Gpa/℃ for tungsten alloy. This also verifies the assumption in Steinberg constitutive model that G′ T should be a constant. When we applied this constant to calculate the corrected shear modulus under shock compression, the calculated results are in accordance with the experimental data.