Plastic deformation mechanism transition of Ti/Ni nanolaminate with pre-existing crack:Molecular dynamics study

Tensile behaviors of Ti/Ni nanolaminate with model-I crack are investigated by molecular dynamics simulations.The Ti/Ni nanolaminates with center crack either in Ti layer or in Ni layer under different loading directions are utilized to systematically study the mechanical performance of the cracked material.The results indicate that pre-existing crack dramatically changes the plastic deformation mechanism of the Ti/Ni nanolaminate.Unlike the initial plastic deformation originating from the interface or weak Ti layer of the crack-free samples,the plastic behavior of cracked Ti/Ni nanolaminate first occurs at the crack tip due to the local stress concentration.Subsequent plastic deformation is dominated by the interaction between the crack and interface.The Ti/Ni interface not only impedes the movement of the initial plastic deformation carriers(dislocation,slip band,and deformation twinning)from the crack tip,but also promotes the movement of interfacial dislocations in the tension process.Microstructure evolution analysis further confirms that the plastic deformation mechanism transition is ascribed to the orientation-dependent tensile behavior at the crack tip,which is intrinsically attributed to the anisotropy of the certain crystal structure and loading direction of the cracked Ti/Ni nanolaminate.In addition,by analyzing the effects of different plastic deformation carriers on crack propagation in specific crystal,it can be discovered that the interfacial dislocations moving towards the crack tip can further promote the crack growth.

Molecular dynamics study of coupled layer thickness and strain rate effect on tensile behaviors of Ti/Ni multilayered nanowires

Novel properties and applications of multilayered nanowires(MNWs)urge researchers to understand their mechanical behaviors comprehensively.Using the molecular dynamic simulation,tensile behaviors of Ti/Ni MNWs are investigated under a series of layer thickness values(1.31,2.34,and 7.17 nm)and strain rates(1.0×10^(8)s^(-1)≤ε≤5.0×10^(10)s^(-1)).The results demonstrate that deformation mechanisms of isopachous Ti/Ni MNWs are determined by the layer thickness and strain rate.Four distinct strain rate regions in the tensile process can be discovered,which are small,intermediate,critical,and large strain rate regions.As the strain rate increases,the initial plastic behaviors transform from interface shear(the shortest sample)and grain reorientation(the longest sample)in small strain rate region to amorphization of crystalline structures(all samples)in large strain rate region.Microstructure evolutions reveal that the disparate tensile behaviors are ascribed to the atomic fractions of different structures in small strain rate region,and only related to collapse of crystalline atoms in high strain rate region.A layer thickness-strain rate-dependent mechanism diagram is given to illustrate the couple effect on the plastic deformation mechanisms of the isopachous nanowires.The results also indicate that the modulation ratio significantly affects the tensile properties of unequal Ti/Ni MNWs,but barely affect the plastic deformation mechanisms of the materials.The observations from this work will promote theoretical researches and practical applications of Ti/Ni MNWs.

Influence of Defects and Crystallographic Orientation on Mechanical Behavior of Nanocrystalline Aluminium

Simulation of molecular dynamics using Embedded Atom Method(EAM) potentials is performed to investigate the mechanical properties of single crystal Al along various crystallographic orientations under tensile loading.The specimens are provided with one or two embedded circular voids to analyze the damage evolution by void growth and coalescence.The simulation result shows that the Young's modulus,yielding stress and ultimate stress decrease with the emergence of the voids.Besides,the simulations show that the single-crystal Al in different crystallographic orientations behaves differently in elongation deformations.The single-crystal Al with 100 crystallographic orientations has greater ductility than other orientated specimens.The incipient plastic deformation and the stress-strain curves are presented and discussed for further understanding of the mechanical properties of single-crystal Al.