13th International Conference on Fracture June 16–21, 2013, Beijing, China -5- Figure 1. Schematic representation of the model to study the behavior of a crack growth Figure 2. Crystallographic orientation of the studied initial crack Figure 3. Edge crack specimen used for the simulation Figure 4. A typical simulation cell with a pre-crack The temperatures in performed all simulations varies in the range of temperature keeping the iron in body-centered cubic crystal structure. The purpose of our research was to probe the influence of temperature on the crack growth behavior, thus the temperature of atoms in simulation was controlled to given value. The temperature of a group of atoms was reset by explicitly rescaling their velocities without performing time integration, unlike the NVT ensemble which performs Nose/Hoover thermostatting and time integration. It only modifies velocities that effect thermostatting. Therefor NVE ensemble using a separate time integration fix was utilized to actually update the positions of atoms using the modified velocities. 4. Results and discussions 4.1. Direct observations of dislocation slip bands The dislocation as a result of atomic movement simualtion results can be shown in graphic mode through developped postprocessing code and VMD. In a general standard display style the dislocation and slip band stripes are not very clear and it is not easy to distinguish them. In terms of Moire interferometry method, an appproach to obtain clearer image of slip band patterns generated by deformed material crystals was put out in this paper by means of adjusting the drawing method, lattice node scale, plot size and screen grid resolution. This approach was called stripe image adjusting technique here. Figure 5 and 6 are two examples after applying proposed stripe image adjusting technique. By utilizing this new method the emission of slip bands from pre-crack tips can be observed clearly and picturesquely with the response of cracks propagating under congstant
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