A Validated Computational Study of Lubricants under White Etching Crack Conditions Exposed to Electrical Fields

Round 1

Reviewer 1 Report

·          The work well done but have some  corrections needed to improve the quality of the presentation. I enlist them below:

 

   The abstract completely needs to be rewritten. The current abstract only describes the general purposes of the article. It should also include the article's main (1) impact and (2) significance of  Lubrication, Bearings, White Etching Cracks. Note that a good abstract should contain aim, methods, findings and recommendations.  In addition, it should cover five main elements, introduction, problem statement, methodology, contributions and results.

·         The text related to the literature analysis should be improved. Authors very often use "this study." One gets the impression that the authors are talking about his study, but the authors describe studies from the literature.

·         The methodology is not clearly described. The description of the applied method should be improved. The authors describe part of the matter of White Etching Cracks (WEC) .

·         What are the advantages and limitations of the model?

·          Why no future research is listed?

·         The actual data validation is missing.

·         Comparison results with the experimental data should be provided and discussed 

 

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

The paper proposes a method to predict the tendency of a lubricant to induce the formation o white etching layers due to electrical arching phenomena based on the ab-initio calculation of the dipole moments of the constituent molecules and their processing to extrapolate a unifying parameter.

The work has considerable fundamental interest as it proposes a novel and potentially very useful predictor; however, some aspects of the calculations and the experimental verification might be improved as follows:

- For non-specialists in chemistry, the PM3 method is not well-known. Could the authors provide a brief explanation and/or one or more references to explain its difference from the more "conventional" DFT method? Are there any specific assumptions and settings that underlie the calculations and that can be specified in the paper apart from the RMS 0.01 convergence criterion?

The indication of RMS 0.01 itself is not fully clear. Is it a room mean square error?

- The same can apply to the use of the atomic units to express the electric field. A reference can be given for non-specialists as the journal's readership might include e.g. engineers with limited knowledge of computational chemistry.

- For a better understanding of the dipole moment calculations in Figs. 2-16, it would be important to know what the x, y, z directions are with respect to each of the molecules in Figure 1. Their structural complexity indeed implies that their responses may vary along different directions, so it would be useful to know along which specific molecular orientation each individual response and interaction are computed. Maybe, the x,y,z axes could be plotted in Fig. 1 next to each molecule.

- Lines 184-186, 190-192 and 195-197 repeat identical text lines to introduce the three graphs in Figs. 2-4. Perhaps, it could be advisable to "condense" those lines in a single textual description of the figures, and maybe the three lines could be themselves plotted onto a single graph for easier comparability.

-  Line 218 states that the subsequent analyses concern systems containing a baseoil component. However, the ZnDDP - Ca-sulphonate systems shown in Figs. 11-16 do not include a baseoil (neither of these constituents is a baseoil).

- Perhaps the main limitation of the paper is the scarcity of direct verification. Table 2 does list references containing experimental results that correspond to some of the analysed combinations; however, for an easier appreciation of how well the predictor matches to those experimental results, is it possible to provide a quantitative or qualitative indication of those results?

- Some of the references lack relevant bibliographic information; for example, there are no volume and page numbers for refs. 1-3; on other cases, references to journal articles are formatted seemingly like they were references to books, like refs. 5, 7-9.

- There might be a few typos and/or unclear expressions:

l. 69: a matter tribo-plasma -> a matter of tribo-plasma

l. 81: the natural question arise -> the natural question arises

l. 90-91: the expression "get them accessed to" seems not fully clear in its context

l. 98: Route Mean Square -> Root Mean Square

l. 151: an external electrical field interfere -> an external electrical field interferes

l. 158: the goal of construct -> the goal of constructing

l. 163: when crossing take place -> when crossing takes place

l. 222: the second reference to Figure 11 is probably a mistype for Figure 12 instead

l. 261: all permutations of the components is -> all permutations of the components are

l. 272: As mostly lubricants are based on -> As most lubricants are based on

l. 277: with a tendency that WEC is more alike: the expression "more alike" is not clear in this context. Does it stand for "more likely"?

Author Response

Please see the attachment.

Author Response File: Author Response.docx