Tensile Properties And Fracture Behaviors Of Low-dimentional Nanomaterials: A Molecular Dynamics Study

In this thesis,we have performed MD simulations systematically to investigate the mechanical and fracture behaviors of monolayer phosphorene(MP)with and without grain boundary,we also have explored the effects of body defects on the elastic and plastic properties of Cu nanowires in different orientations under tension,respectively.(1)In order to study the effect of grain boundary on the mechanical behavior and fracture mechanism of the MP under tensile forces,five different grain boundaries of MP were studied.As a contrast,the fracture mechanism of MP without grain boundaries stretched in different directions has also been studied.Our findings show that although the bonds in zigzag direction are stronger than those in armchair direction for MP,the fracture mostly occurs on the bond in zigzag direction as stretched randomly.And both the fracture strength and stain depend on the stretching direction,i.e.the fracture strength increases while the fracture strain decreases when the tensile direction is close to the zigzag direction.In the case of MPGB,the crack formed at the GB and propagated perpendicular to the stretching direction under parallel tension to the GB,while it spreads along the GB under perpendicular tension to the GB.Moreover,the existence of GB results in a decrease in the Young's modulus and the fracture strain,whereas has a little influence on the largest fracture strength.Our calculations also indicate that all of the Young's modulus,the fracture strength and strain decrease with increasing temperature.As for the strain rate effect,it has little influence on the fracture behavior.(2)Using the MD method,we have studied the influences of body defects on the deformation of nanowires in <100>,<110> and <111> orientations under tension,respectively.To avoid the size effect from the body effect,the radius of the body defect is changed from 1.8 to 10.83 ?.We found that the existence of body defect leads to a decrease of the mechanical properties of Cu nanowires in the elastic stage,but the Young' moduli of the three oriented nanowires change slightly with the radius of body defects,illustrating that body defects have little influence on the elastic properties of nanowires.In the plastic deformation stage,most of the body defects lead to a decrease of the plastic properties of <100> oriented nanowires,whereas the body defects in <110> and <111> oriented nanowires present opposite effects,they lead to an improvement in the plastic properties of both <110> and <111> oriented nanowires.Hence,it is clear that body defects not only can weaken the plastic properties of Cu nanowires,but also can improve their plastic properties,it depends on the orientations of nanowires.