Shielding hyper-velocity impact ( HVI) from space debris is of great concern in the de-sign of spacecraft, while strong nonlinearities in HVI process pose great challenges to traditional nu-merical methods. As one kind of recently developed meshfree methods, material point method ( MPM) can easily deal with extremely large deformation, fracture and fragmentation, and large number of contacts appearing in HVI process. Owing to the above advantages, MPM is very suitable for solving HVI problems. In recent years, the authors improved MPM theory in several aspects, de-veloped three-dimensional MPM software system MPM3D, and numerically investigated HVI process of space debris in detail. Numerical results agree well with experimental results. Typical phenomena including excavation, spalling, and debris cloud can be reproduced correctly. The energy absorption and shielding capability of foam material and honeycomb material can be easily studied based on models of material internal structure. The above simulations demonstrate that MPM and MPM3D software are powerful numerical tools for HVI problems.

The equation of state (EOS) plays an important role in high-velocity impact process since phase transformation, melting, and even vaporization may happen under such extreme loading conditions. It is desired to adopt an accurate EOS covering a large range of points in the phase space. This paper proposes a combined molecular dynamics and material point method approach to simulate the high-velocity impact process. The EOS data are first obtained from a series of molecular dynamics computations, and the parameters are fitted. Then the EOS parameters are adopted in the material point method simulation to model the impact process. Simulation results show that the fitted EOS can be very accurate compared to experimental results. The shape of the debris cloud obtained by our multiscale method agrees well with that of the experiments. An empirical equation is also proposed to predict the fraction of melting material in the high-velocity impact process.

Based on the characteristics of Material Point Method(MPM) in the simulation of hypervelocity impact and explosion problems,the extension on MPM and its application are introduced,including the application hypervelocity impact problems by using MPM,material point finite element method(MPFEM),hyprid MPFEM,an adaptive particle splitting scheme for MPM,contact algorithm based on local multiple background mesh,and parallel MPM algorithm.Based on the improvement,a 3D explicit parallel simulation software MPM3D is developed for impact and explosion problems.C + + is used to develop MPM3D and the graphical user interface PeneBlast is developed by Qt and VTK.MPM3D can run on different platforms such as Windows,Linux,Mac OS,and so on.Many examples about hypervelocity impact,penetration,explosion,slope failure and metal cutting verify the reliability and accuracy of MPM3D.MPM3D can be an effective design tool for spacecraft protection on space debris,conventional weapon development and protection,and so on.

In the smoothed molecular dynamics (SMD), the high frequency modes are eliminated from the motion of atoms to enlarge the time step significantly. In some situations, however, rearrangements or atoms disorder may occur. Hence, it is desirable to use MD in localized regions to capture the interesting high frequency motion, while use SMD elsewhere to save the computational cost. In this paper, an adaptive smoothed molecular dynamics (ASMD) is developed. During the simulation process, if the high frequency motions of atoms are dominant in a region, the background grid in the region is refined hierarchically until it is able to capture the high frequency motion of the atoms.

A parallel smoothed molecular dynamics (SMD) method is proposed. Parallel programs with SMD and SMD-MD coupling are developed for loading problems of a plate with a crack and a nano single crystal copper beam subjected to remote tensile. With traditional molecular dynamics, smoothed molecular dynamics method introduces fixed background mesh and solves motion equations. Critical time step in SMD is controlled by background grid size and could be enlarged to save simulation time. Results are in agreement with those of traditional molecular dynamics. Compared with traditional MD simulation, SMD and SMD-MD coupling methods save computing time.