The Effects of Dislocation Dipoles on the Failure Strength of Wrinkled Graphene from Atomistic Simulation

Round 1

Reviewer 1 Report

The manuscript contains interesting and useful results on the fracture and mechanical properties of rippled graphene containing dislocation dipoles and certainly deserves publication in Applied Sciences. In their study, the authors employed atomistic simulations. The methodology and the results are clearly presented. An issue always relevant in this type of work is how the results depend on the atomistic modeling. Thus, my only suggestion to the authors is to (at least partially) demonstrate that their main findings are reproduced by a different atomistic potential. Such a demonstration will add to the reliability of their findings. 

Author Response

We are very grateful for the great efforts and valuable suggestions made by the Reviewer. We have revised the manuscript accordingly. The detailed response to the comments of the Reviewer is provided below together with the description of the changes applied to the manuscript. We note that all changes to the manuscript are highlighted in red for the convenience of the reviewer.

 

Comment 1

The manuscript contains interesting and useful results on the fracture and mechanical properties of rippled graphene containing dislocation dipoles and certainly deserves publication in Applied Sciences. In their study, the authors employed atomistic simulations. The methodology and the results are clearly presented. An issue always relevant in this type of work is how the results depend on the atomistic modeling. Thus, my only suggestion to the authors is to (at least partially) demonstrate that their main findings are reproduced by a different atomistic potential. Such a demonstration will add to the reliability of their findings.

 

Reply:

We appreciate the comment. Surely, the used interatomic potential may crucially affect the obtained results. To date, different potentials were developed to study graphene behavior, for example, AIREBO, BOP, Tersoff, and Brenner. We agree that results can differ, thus we made additional calculations with Tersoff and Brenner potential. However, AIREBO and Brenner are very close, and AIREBO even can reproduce more different movements in the structure, thus we have added a new figure 4 where results for AIREBO and Tersoff are compared since the results are a bit different. As can be seen from new figure 3, at the initial stages of tension, the behavior is very close, but finally, the fracture mechanisms are different. We add some additional verification of the used potential to the text and also discuss these new results in the text (highlighted in red).

Reviewer 2 Report

This paper investigates the effects of dislocation dipole on the tensile mechanical properties of graphene based on molecular dynamics simulations. The authors presented the MD results of various graphene under tensile loading, which are clearly structured. However, the effects of defects on graphene’s properties have been widely studied before. The significance and novelty of this study are not really clear, which should be more highlighted. The detailed comments are given below, which should be fully addressed before the reconsideration.

1.     Page 2, Line 44, the two Refs are both listed as 32.

2.     Page 3, what is the viral stress?

3.     The tensile strength and Young’s modulus of pristine graphene are about 8 GPa and 16 GPa, respectively in your paper which are far lower than the universally accepted experimentally measured and theoretically predicted values (~130 GPa and ~1 TPa). Besides, the shapes of the stress-strain curves are questionable. What is the reason? More convincing explanation should be given.

4.     It seems that the dipole arm does not have obvious effects on the mechanical properties of graphene. So this discussion of the effect of dislocation dipole might be meaningless.

5.     Why are the wrinkles appeared in the graphene during the tensile process?

Author Response

We are very grateful for the great efforts and valuable suggestions made by the Reviewer. We have revised the manuscript accordingly. The detailed response to the comments of the Reviewer is provided below together with the description of the changes applied to the manuscript. We note that all changes to the manuscript are highlighted in red for the convenience of the reviewer.

Comment 1

Page 2, Line 44, the two Refs are both listed as 32.

 

Reply:

We thank the reviewer for such a careful reading. We fix this misprint.

 

Comment 2

Page 3, what is the viral stress?

 

Reply:

We thank the reviewer for such a careful reading. Again, it was a misprint. We mean that various components are calculated. The misprint is fixed.

 

Comment 3

The tensile strength and Young’s modulus of pristine graphene are about 8 GPa and 16 GPa, respectively in your paper which are far lower than the universally accepted experimentally measured and theoretically predicted values (~130 GPa and ~1 TPa). Besides, the shapes of the stress-strain curves are questionable. What is the reason? More convincing explanation should be given.

 

Reply:

We appreciate the comment. In the present work, crumpling of graphene is allowed with the aim to consider the effect of natural graphene rippling on fracture strength. It is known that the deformation energy in free-standing graphene can be easily released through the formation of out-of-plane wrinkles, which simultaneously soften graphene. The type of ripples considerably affects the elastic modulus and fracture strain and strength [34,35]: if there are small-amplitude corrugations of graphene, the fracture strength and elastic modulus are lower, but not so notably in comparison with the high-amplitude ripples. Thus, such low values are explained by the appearance of ripples which is in agreement with the literature. It is highlighted in the text in red color.

 

Comment 4

It seems that the dipole arm does not have obvious effects on the mechanical properties of graphene. So this discussion of the effect of dislocation dipole might be meaningless.

 

Reply:

We appreciate the comment. In fact, for fracture strength, it is really not meaningful, but still important since before this study we did not understand if it would be important or not. But the interesting point is that the dipole arm will affect the dislocation dynamics, which is known and, also, affect the wrinkling of graphene. Moreover, there is a connection between wrinkling and fracture strain and stress. Since we did not highlight that, we have added more discussion on this (colored in red).

 

Comment 5

Why are the wrinkles appeared in the graphene during the tensile process?

 

Reply:

We appreciate the comment. It was shown in [32,33] that at positive strain values along one direction and negative strain values along the other direction, graphene loses its stability, and ripples with different orientations appear. Here, when we stretch graphene along one direction simultaneously shrinkage is allowed along the normal direction, which results in positive stress along one axis (tension) and negative stress normal (compression). Thus, this scenario is known from the literature and in good agreement. Additional descriptions are added to the text.

Round 2

Reviewer 2 Report

The paper has been improved and can be accepted.

Author Response

We thank the reviewer for his positive decision. We additionally checked English and fixed misprints.