Multiscale Numerical Simulation Of Hypervelocity Impacts

More and more space debris are produced with the development of spaceflight. The high speed debris are a great threat to the cause of spaceflight. Hypervelocity impacts of space debris can result in melting or even evaporating. The complex phenomena can not be accurately described by the continuum mechanics. Here we attempt to model the phenomena with a multiscale method. The following progress is made.The material point method (MPM) is extended to model hypervelocity of macro-bodies. The discrete forms of the conservation equation of energy and the equation of state are given. In MPM, we modify the standard finite element interpolation functions which usually produce artificial forces on hierarchical background grids and that effectively reduce artificial forces on hierarchical background grids. We propose a new multiscale simulation method which seamlessly combines the conventional molecular dynamics (MD) with the continuum mechanics which is formulated under MPM. The seamlessness is validated by dynamic and static tests. The method is suitable for pair, triple and many-body potentials. The multiscale method proposed here is implemented to study the process of hypervelocity cluster impacts. For Cu cluster impacting an infinitely large Cu substrate, a reliable potential and a reasonable identification method of displaced atoms are adopted. Simulation results show that in the process of impact displaced atoms propagate anisotropically, and predominately along the interaction lines of slip planes. For Si-Si impacts, displaced atoms also, though less dramatic, propagate anisotropically. All above indicates that the underlying lattice structure plays an important role in the process of hypervelocity cluster impacts, leading to an anisotropic energy transportation process. Influence of cracks on hypervelocity impact is also addressed.