Comparison of fracture behavior of defective armchair and zigzag graphene nanoribbons

Abstract

Molecular dynamics simulations of armchair graphene nanoribbons and zigzag graphene nanoribbons with different sizes were performed at room temperature. Double vacancy defects were introduced in each graphene nanoribbon at its center or at its edge. The effect of defect on the mechanical behavior was studied by comparing the stress-strain response and the fracture toughness of each pair of pristine and defective graphene nanoribbon. Results show that the effect of vacancies in zigzag graphene nanoribbon is more profound than in armchair graphene nanoribbon. Also, the effect of double vacancy defect on the ultimate failure stress is greater in zigzag graphene nanoribbons than in armchair graphene nanoribbon due to bond orientation with respect to loading direction. Strength reduction can be as high as 17.5% in armchair graphene nanoribbon with no significant difference between single and double vacancies, while for zigzag graphene nanoribbon, the strength reduction is up to 30% for single vacancy and 43% for double vacancy defects. It is observed that for zigzag graphene nanoribbon with double vacancy at the edge, the direction of the failure plane is oriented at AE30 with respect to the loading direction while it is always perpendicular to the direction of loading in armchair graphene nanoribbon. Results have been verified through studying the fracture toughness parameters in each case as well.

Atomistic Modelling of Size-Dependent Mechanical Properties and Fracture of Pristine and Defective Cove-Edged Graphene Nanoribbons

“…Therefore, the red broken lines illustrate the broken bonds of the system, but they do not represent the actual bond lengths. Such representations are commonly used in molecular simulations to illustrate failure patterns, etc., e.g., [ 22 , 46 ]. It is observed that the defects SW1 ( Figure 10 a) and 5555-6-7777 ( Figure 10 c) have a horizontal plane of symmetry and two pentagons at the front of the defects.…”

“…One of the most common defects in the GNR [ 53 ] is caused by atomic vacancies. Several studies [ 22 , 36 , 54 ] have examined the effects of vacancies, such as divacancy (DV) and other vacancy configurations, on the mechanical and electronic properties of GNR along the ar and zz directions. In this section, we extended the single DV defect study presented in the preceding section to examine the mechanical response of a defective CGNR containing a single DV defect with different orientations and multiple DV defects.…”

“…All molecular dynamics (MD) simulations are carried out at temperature of 1 K with temperature controlled by the Nose-Hoover thermostat. This thermostat has been widely used for carbon systems and is known to yield stable and efficient computations [ 20 , 21 , 22 , 24 , 37 , 40 , 44 ]. The timestep was 0.5 fs and a uniaxial tension was applied after the system was relaxed at zero pressure through isothermal–isobaric ensemble (NPT).…”

“…The armchair ( ar ) and zigzag ( zz ) edges are the most investigated types by both theoretical and experimental approaches. Several studies using molecular dynamics (MD) simulations [ 20 , 21 , 22 , 23 , 24 ], atomic-scale finite element method [ 25 ] and experimental measurements [ 26 , 27 ] have been used to investigate the mechanical properties of GNR along the ar and zz directions. A study of the electronic properties of zigzag graphene nanoribbons with constructed edges representing pentagonal and heptagonal defects has been presented by Pincak et al [ 28 ], whereas the effects of edge vacancies on the electronic properties of zigzag nanoribbons have been addressed by Smotlacha and Pincak [ 29 ].…”

“…Several studies [ 20 , 22 ] using MD simulations have been used to study the mechanical properties and the fracture patterns of the defective ar and oz. GNR (AGNR and ZGNR, respectively).…”