Molecular Dynamics Simulations Of Fatigue Deformation In Polycrystalline Ti

Metal in the manufacture and use of the process will inevitably occur fatigue deformation,and with the fatigue time,the material will be destroyed and failure.Therefore,the evolution of microstructures in the process of fatigue deformation have a great significance to the production and use of materials.At the microcosmic level of material research,molecular dynamics simulation is an important tool in computer simulation.According to this method,the fatigue process of the polycrystalline titanium model without cracks and crack is simulated in this paper.In this paper,the research status of molecular dynamics simulation method in the material science has been summarized.The methods and principles of molecular dynamics simulation are introduced,and the key factors and methods of each process are discussed in detail.Fatigue deformation process is studied by strain loading method,no crack and crack model.For the no crack model,the tensile behavior of the polycrystalline is studied first to obtain the basic mechanical properties of the titanium polycrystalline.Then,under the fatigue load,the fatigue behavior of the material is observed and analyzed by drawing the true stress and strain map of the material and the atomic pattern of the special moment.According to the energy change map,the whole fatigue deformation process is described in detail.And studied the effect of grain size on fatigue deformation process.The results show that the internal dislocation of the grains leads to plastic deformation of the structure and the dislocation occurs in the grains at the grain boundary,and then moves to the grain boundary opposite the grain and disappears gradually;The grain boundary is the source of dislocations,movement and annihilation,grain coarsened;And when the grain size is 5 nm and 8 nm the fatigue deformation is dominated by dislocation nucleation,movement and annihilation;When the grain size is 10 nm,the fatigue deformation is dominated by the grain boundary movement.For the crack model,the fatigue process of some special moments is described in detail,and the fatigue deformation behavior is further explained by the energy change map.The effects of crack length,temperature and strain rate on the fatigue deformation process were discussed.The results show that with the increase of crack length,the internal energy of the system increases,the system becomes more unstable and is more prone to deformation.The crack tip has a small range of yield,the crack around the elastic area constraints its plastic deformation make the crack closed trend;With the increase of temperature,the elastic modulus of the material becomes larger,the stress in the system becomes smaller,and the plastic deformation is more likely to occur in the system.When the temperature is 1000 K,the grain is fused into one in the system,and the dislocation within the system is evenly distributed on the crack surface and the surface.With the increase of strain rate,the yield stress and yield strain of polycrystalline titanium also increase,and the total energy and energy change in the system is larger.