13th International Conference on Fracture June 16–21, 2013, Beijing, China -3- Table1. EAM potential parameters of titanium Re(Å) fe ρe α β A B µ κ 2.933872 1.863200 25.56513 8.775431 4.680230 0.373601 0.570968 1.0 0.5 The potential function usually is empirical, and it is also controversial in MD simulation. The melting point of α-Ti was obtained by LAMMPS in order to verify the EAM/alloy potential. The atomic structure of α-Ti is shown in Fig.1. The initial configuration of the simulated system was composed of 8×8×5 HCP-Ti cellular, a total of 1280 atoms, the time step was 0.01ps, using three-dimensional periodic boundary conditions, let the system in the 2.5K relaxation 500000 steps, and then use the Nose-Hover method to keep the pressure around zero, and then elevated system temperature from T=2.5K to 2500K. During the simulation, the thermodynamic results were output every 1000 steps, as shown in Fig.2 and Fig.3 respectively. The average atomic volume almost linear increases with the temperature and simulation time in the heating process. But it suddenly jumps 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- Ti is about 1951K, and simulation value is 1943K near a phase transition. The error between them is about 0.41%. Such deviation derived from the melting point between the MD simulation and the actual sample were relatively consistent, which was related with using three-dimensional periodic boundary conditions in simulation system, the limited number of particles and the accuracy of interaction potential. The EAM/alloy potential function parameters, which were evaluated by melting point test were shown in Table1. Figure 2. The mean volume of single atom changing with temperature during heating process. Figure 3. The mean volume of single atom changing with modeling time during heating process. 3 Specimen setup Due to anisotropic characteristic of α-Ti, it is very meaningful for comprehending failure mechanism of material on different conditions of loading. The MD models with different loading directions used for conducting fracture studies were shown in Fig.4 and 5. The MD model in Fig.4 showed that the loading direction was[0110], while it was [0001]in Fig.5. The dimensions in the x-y plane are 200Å×204Å with thickness in the z-direction
RkJQdWJsaXNoZXIy MjM0NDE=