Atomistic computer simulation of fracture process at nanoscale

Fracture of materials and structures is a classic problem in the discipline of solid mechanics. Traditional continuum mechanics has successfully solved many important problems and contributed much to engineering, while some problems still remain, such as microscopic fracture process, which requires us to go deep into the atomistic scale, nanomechanics. In this paper, our Work of atomistic computer simulation of fracture process at, nanoscale has been presented, as well as some selective work of others has been reviewed. To facilitate the numerical simulation at nanoscale, a new units system has been developed, including length, time, mass, and other derived physical qualities. Molecular dynamics simulations have been conducted to investigate the I-type brittle crack propagation and fracture process of single crystalline silver using two-dimensional triangular lattice model. The velocity Verlet algorithm is implemented to integrate the equations of motion. The Sutton-Chen potential is used to represent atomic interactions in our simulation. The behaviors of bifurcation and post-bifurcation have been demonstrated by atomic images. These characteristics. have been experimentally observed, however continuum fracture theories can not provide reasonable explanation to them. The traditional fracture mechanics predicts that the crack surface is mirror-like smooth, while a roughening transition is found in our atomistic simulation. Deeper insights into the fracture process can be obtained with multi-scale model to couple different energy, length and. time scales. The most important of all is that the couple model must be seamless. This problem has not been completely solved yet. Some promising models and methodologies have been presented. One is quasi-continuum method. The basic idea is that one can consider an inhomogeneously deformed body as a continuum, for which the kinematics can be described entirely in terms of displacement field, while atomistic analysis is employed to determine the total energy of the body. Another method of seamless coupling of quantum to statistical to continuum mechanics is using handshaking region between two different length scales. This method combines tight-binding (TB), molecular dynamics (MD) and finite element (FE) techniques. Its unifying theme is that a Hamiltonian is defined throughout the entire system. The third method is coarse-grained molecular dynamics (CGMD), where the FE/MD coupling is based on a derivation of the physical. scaling properties of the system.