13th International Conference on Fracture June 16–21, 2013, Beijing, China -3- the temperature and simulation time in the heating process, which turn upsuddenly increases when the temperature reaches a certain value. This phenomenon indicated that the system had undergone some kind of phase transition. The melting point of α-Fe is about 1873K, and simulations in the 1990K near a phase transition, increased by 6.2% than its equilibrium melting point. Such deviation derived from the melting point between the MD simulation and the actual sample were relatively common, which was related with using three-dimensional periodic boundary conditions in simulation system, the limited number of particles and the accuracy of interaction potential. 1990 11 11.5 12 12.5 13 13.5 14 14.5 0 500 1000 1500 2000 2500 3000 Volume per atom (Å^3) Temperature (K) 11 11.5 12 12.5 13 13.5 14 14.5 0 1000 2000 3000 4000 5000 6000 7000 Volume per atom (Å^3) Time (ps) Figure 1. The mean volume of single atom changing with temperature during heating process Figure 2. The mean volume of single atom changing with modeling time during heating process In the simulation, the system contains two elements, i.e., Fe and C .The Fe/C alloy EAM/FS potential function parameters[13], which were evaluated by melting point testing were adopted in this work. 2.2. Specimen setup The MD model used for conducting fracture studies is shown in Fig. 3. The dimensions in the x-y plane are 200Å×192Å with thickness in the z-direction equaling 8.82Å.The total atoms of the model were 31978. The x y z coordinate system represents the lattice directions [0 1 0], [1 0 0] and [0 0 1] respectively. In the model free boundary conditions were used in the x- and y-directions, while it was periodic boundary in the z-direction. As shown in Fig. 3, the simulation domain is divided into three regions. Atoms that are in regions 1 and 3 are boundary atoms through which tensile load are applied. A crack of length 100Å was generated at the interface of Fe3C and α-Fe. During MD simulations of tensile crack propagation, the system is uniformly stretched (by moving each atom a distance corresponding to a uniform normal strain increment) in the Y-direction at each time step[2]. And the duration was less than 0.001ps, which made it relax freely till the valley of energy status. Molecular dynamics simulation time step was given with t=0.001ps. Integral calculation on system movement equation through Verlet techniques was applied during simulation. The simulation process: applying NVE system tracking and in every time step, maintain the temperature (300K, 473K and 673K) constantly through re-calibration of the speed of atoms. Firstly perform static relaxation to bring the system to the minimum energy status, and applying 3.128Å/ps strain rate in y direction. A systematic analysis on the effect of strain rate was not conducted in this study.
RkJQdWJsaXNoZXIy MjM0NDE=