Numerical Simulation And Interatomic Potential Development For Mechanical Behavior Of Metal Material At High Strain Rate

The mechanical properties of metal materials are closely related to factors such as their composition and microstructure.The failure behavior of materials is mainly due to the effects of dislocations,stacking faults,grain boundaries and twin boundaries.In this paper,the effects of microstructure and temperature on the mechanical properties and plastic deformation mechanism of TiAl alloys were studied at the atomic scale using molecular dynamics methods.Accurate atomic interaction potential is an important prerequisite to ensure the reasonable and reliable molecular dynamics simulation results.In order to further study the mechanics of materials,this article takes the rutile TiO₂ material as an example,and carries out exploratory research on the construction of potential at electronic scale.Based on the first-principle,the interatomic potential of the material was constructed.The results of existing literature research have verified the correctness of the constructed potential accordingly.Using LAMMPS software as a simulation platform,the effects of grain size and temperature on the mechanical properties and deformation mechanism of TiAl alloy under uniaxial tensile load were studied by molecular dynamics method.The results showed that,for a grain size of<8 nm,the yield stress of the nano-polycrystalline TiAl alloy increased with increasing grain size?inverse Hall-Petch relation?.Such a plastic deformation was mainly the result of the migration of grain boundaries?GB?and grain rotation.When the grain size exceeded 8 nm,the sensitivity of yield stress on the grain size decreased.The dislocation slip and the deformation twin in the interior of the grain gradually dominated the plastic deformation.With increasing grain size,the Young's modulus also increased.The temperature also influenced the Young's modulus.Increasing the temperature resulted in an increase of the distance between atoms,which decreased the bonding force between atoms,and thus decreased the Young's modulus.With increasing temperature,the dislocation density decreased and the time of dislocation emission on the GB delayed.At the same time,the effects of micro-defects such as twin boundaries and temperature changes on the mechanical properties and micro-deformation mechanisms of nano-polycrystalline TiAl alloys under tensile and compressive loading were also studied.An obvious tension-compression asymmetry in flow stress was found at a temperature of 300K.Increasing the Twin Boundary Spacing?TBS?resulted in an increase of 14.9%in the average flow stress of nano-polycrystalline TiAl alloy under compression compared to that under tension,whereas this value increased to 29.9%when the temperature increased to 600K.When TBS was gradually reduced,the flow stress first increased and then decreased.This was mainly because the change of TBS resulted in the transformation of the plastic deformation mechanism of nano-polycrystalline TiAl alloy.For a TBS of less than or equal to 2.16 nm,partial dislocations nucleated and emitted at the grain boundary and moved parallel to the twin boundary.For a TBS exceeding 2.16 nm,dislocations nucleated and emitted at the intersection of twin boundary and grain boundary,and intersected with the twin boundary eventually.The critical TBS value for this transition was also affected by temperature.The critical TBS value was 3.59 nm at 600 K,which is greater than the critical TBS 2.16 nm at 300 K.Finally,an interatomic potential for molecular dynamic?MD?simulation of rutile TiO₂crystals was developed based on Buckingham potentials.MD simulation was conducted using the developed potentials to obtain various physical parameters?e.g.,lattice constant,bulk modulus,shear modulus,and elastic modulus?of rutile TiO₂ crystals.Results based on the developed potentials were then compared with the experimental results and first principles calculations.The results indicated that the developed interatomic potentials can accurately calculate various physical parameters?e.g.,lattice constant,bulk modulus,shear modulus,and elastic modulus?of rutile TiO₂ crystals.Calculated based on the developed potentials,the melting point of rutile TiO₂ was highly consistent with the experimental values.This high consistency demonstrates the validity of the developed potentials.