MOLECULAR-DYNAMICS SIMULATION ON LASER-ABLATION OF FCC METAL

Considering the principle of minimum potential energy and thermal expa nsion, atomic array model of fee metal is constructed al room temperat ure through molecular dynamics, where 12,000 atoms are arranged in 60 atoms per layer in the direction of width and 200 layers in the direct ion of depth. It is confirmed that velocity of atoms at room temperatu re has a Maxwell distribution. A simple model of laser absorption of c rystal and a method to estimate stress state of atoms are proposed. Ap plying molecular dynamics, atomic behavior of copper, aluminum and lea d during laser ablation is simulated. Variation of atomic array and st ress state of atoms during and after laser irradiation are shown visua lly. Main conclusions obtained are summarized as follows: (1) Thermal shock wave travels to interior of material with laser irradiation. Esp ecially, when surface vapors explosively, large compressed-field occur s due to its reaction. (2) Propagation velocity of thermal shock wave is equal to elastic wave velocity. (3) Particles scatter in pieces as relatively fine cluster when power density is higher. On the other han d, the vicinity of surface bounds out forming relatively large lumps w hen power density is lower. (4) Degree of these phenomena varies with material and depends on the well depth of pair potential.