Abstract: The microscopic mechanism of metal film crack extension under impact loading was investigated. Molecular dynamics method was adopted to simulate Cu metal film， and the system kinetic energy， stress， strain and microstructure charts were obtained with surface cracks under impact loading. When the system stress shifted from compressive stress to tensile stress， the atoms on the crack got large kinetic energy， and atoms on crack tips began to sputter， then vacancies appeared in the crystal lattice. When tensile stress reached 364385MPa， lattice vacancies extended to blunt cuts， and the crack grew. The results show that the change of the system energy and stress causes bluntcut damage to the microcrack tips， which is the main reason of metal film crack extension under high speed impact loading.

Key words: impact loading, metal film, crack extension, molecular dynamics, bluntcut damage