Molecular dynamics simulations were performed to study the diffusion behavior of hydrogen atoms in body-centered cubic(bcc) tungsten(W). The energy distribution of a single hydrogen atom in the (001) plane of tungsten lattice was computed. The values of diffusion barriers agree well with other theoretical and experimental results. The interaction between an H atom and a vacancy was simulated, which shows evidence of strong binding effect. The temperature effect on the diffusion behavior of hydrogen atoms was investigated. The critical temperature for an H atom to diffuse in bulk W with and without vacancies were calculated to be 950 K and 450 K, respectively, which is supported by several experimental results. In addition, the diffusion coefficient of hydrogen atoms in tungsten was evaluated and analyzed.
In this paper the macroscopic damping model for dynamical behavior of the structures with random polycrystalline configurations at micro–nano scales is established.First, the global motion equation of a crystal is decomposed into a set of motion equations with independent single degree of freedom(SDOF) along normal discrete modes, and then damping behavior is introduced into each SDOF motion.Through the interpolation of discrete modes, the continuous representation of damping effects for the crystal is obtained.Second, from energy conservation law the expression of the damping coefficient is derived, and the approximate formula of damping coefficient is given. Next, the continuous damping coefficient for polycrystalline cluster is expressed,the continuous dynamical equation with damping term is obtained, and then the concrete damping coefficients for a polycrystalline Cu sample are shown. Finally, by using statistical two-scale homogenization method, the macroscopic homogenized dynamical equation containing damping term for the structures with random polycrystalline configurations at micro–nano scales is set up.
