13th International Conference on Fracture June 16–21, 2013, Beijing, China -2- growth in metals is considerablt complicated than current model postulation. The fracture mode of steels appears as ideal cleavage under low temperatures condition. The currently most widespread model for brittle crack growth in metals proposed by Rice and Thomson is that the high stress concentrations at the crack tip causes bond breaking in the cleavage plane and promotes dislocation emission from the crack tip. A successfully emitted dislocation will slightly blunts the crack tip. At very low temperatures the nucleation and/or removal of dislocations near the crack tip is suppressed, while at higher temperatures this constraint is relieved as a result of the thermally activated nucleation of dislocations. All these phenomena initiate at the atomic scale and form macroscopic consequences. As continuous advances on microscopic physics science and high speed development of computer technology, the molecular dynamics method is widely applied to analyze crack propagation mechanisms[3-14]. Utilizing molecular dynamics method not only a great deal of valuable micro-behaviors can be got but also the macro-properties of a material can be reproduced[15]. The behavior of crack growth in metals depends strongly on the structure evolution of the crack tip, load type and temperature. But at present it is still a lack of research on the influence of temperature on crack growth. The aim of our research was focus on the effect of temperature on crack growth in α-Fe by using numerical simulations. For this purpose large scale molecular dynamics was applied to study the mechanisms of a crack growth under different temperature. Molecular simulations can reveal some crack propagation behavior in atomistic scale and offer a better understanding about crack growth. It even enhances an accurate evaluation method on crack growth and fracture behaviors at extreme temperature. In present paper a model with constant rate of straining load in tension mode I and free surfaces was considered. Symetrical strain proportional to an atomic position in some dimension is imposed to all atoms. Periodicity along the thickness dimension z was applied. Here atomistic simulations were applied to model the process of crack growth in steels under different temperature. The embedded atom method (EAM) potentials belonging to many-body interatomic potentials[1], which provide an essentially better description of the inter-atomic interactions and free surfaces, were employed to get accuracy results. The simulation parameters such as box geometry, timestep, loading rate were determined after performing parameter sensitivity analysis. The computation is implemented by utilizing large-scale atomic/ molecular massively parallel simulator (LAMMPS)[16], Visual Molecular Dynamics (VMD) [17] and developped programs in Python. The simulation results demonstrated that with a crack growing the phenomena involving crack tip passivation, crack opening distance increment, dislocation emission, dislocation slip, plasticity deformation, voids formation and voids coalescence have been appeared and can be observed. Slip bands formation at the crack tips and ligament region and their development with incremental strain and temperature were demonstrated during crack growth. The crack growing with same initial state behaves differently under different temperature. It means that the crack growth trace and fracture configuration are realted with temperature. The dynamic radial distribution function and corresponding number density integral for variable time and temperature were calculated to explorer the relationship between the crack growth and temperature. In this paper, the profile evolution of the crack tip for crack propagation system (0 0 1)[010] in α-Fe at low and high temperatures was investigated. It is expected to probe whether crack growth properties have relationship with some parameters referring to radial distribution function in α-Fe during crack propagation at different temperatures. Some phenomenological descriptions on temperature-dependent relations allowing to predicting crack growth were proposed. The crack growth process, radial distribution function, atomic stresses in a bcc iron single crystal were analyzed utilizing molecular simulations with LAMMPS. Edge crack specimens under tentional strain loading were selected as simulation models. Limited by volume of the paper, here we only provide some key results. Other contents will be reported elsewhere. 2. Crack growth and temperatrue
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