Evaluation of Damage Process of a Coating by Using Nonlinear Ultrasonic Method

Round 1

Reviewer 1 Report

Dear authors,

Please consider the suggested comments to improve the quality of the current version of the manuscript:

1. In the current version of the abstract, only the summary of the work is mentioned in a very broad view. Instead please include specific details of the research work presented in the manuscript. The abstract needs to be incorporated with the gist of the complete work in the manuscript.
2. Please include the details of the technical limitations of the current/previous studies performed by the peers in this specific research point: of damage process of the coating. Also, please include the details of acoustic nonlinear parameters that are used as the early damage index of the coating.
3. Please update the abstract with the experimental conditions, parameters considered, and scientific advancements made as the abstract of a scientific research paper should be precisely mentioning the specific research question that is answered, experimental conditions, operational parameters, results, and conclusions. The current version of the abstract is more as an introduction to the study & research performed rather than explaining the specific scientific advancements made.
4. In the abstract, kindly incorporate the specifications and the quantification of results to have the reader understand the magnitude of the results and to support the conclusion driven. For example, in lines 15-17, it was mentioned that The result shows that there is a significant increase in the nonlinearity parameters with the increasing tensile stress…. But the details and specifications of the results are not included in the current version of the abstract.
5. In the introduction, please include additional background about nondestructive coating methods and their effectiveness, with appropriate references.
6. In the introduction, please specify the need for the current work presented in the manuscript. Very importantly, please include the knowledge gaps existing in the current research work and prior studies performed in the field.
7. It is very important to provide the future scope of the research performed to make a strong impact on the readers on the research performed/Study proposed. In the last paragraph of the introduction, kindly include the details of the broader impacts on the study made and the results achieved.
8. Please update figures 3, 4, 5, and 7 with high-quality images in the manuscript.
9. In the results and discussion section, figure- 7 (a, b, c,& d) needs to be explained and discussed with the logical & scientific conclusions driven from the results (plots). Also, the arguments need to be supported by the ongoing research results with appropriate references.
10. In the results and discussion section, please include an additional quantitative comparison study between the relative measurements of non-linear parameters and stresses.
11. Please revise the manuscript with English grammar. There are many places that the manuscript needs to be improved with respect to English writing.

Author Response

Dear Reviewer：

Thank you for your comments. We have carefully considered and adopted the comments you proposed in the text and revised the paper, which greatly improved the quality of the submitted manuscript. Thank you again for your help in reviewing the manuscript. Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Dear Authors,

Based on the reading of your work in my opinion you obtain a valuable  paper in a topic related to evaluation of coating cracks by ultrasonic nonlinear method. I recognise the efforts Authors have put into this work. 

The article contains experimental tests of the coating under stress and assessment of its damage. The Authors correctly determined the need for development of diagnostic parameters that could determine the condition of the coating during operation, especially coatings subjected to external loads. The structure of the article is clear and logical. However, in my opinion the manuscript needs to be improved in some fields.

Evaluation of the paper general remarks:

• The Abstract section should present quantitative results and not only the most important qualitative results and/or generic considerations. Therefore, significant improvements are expected.
• In several places in the article, e.g. line 90, 94, 104, 106, 108, 110 and so on, the Authors use the personal form (e.g. "We assume that the general...". This is not correct in high-quality articles. It suggests modifying those parts of the article in which the personal form was used.
• What are the dimensions of Al2O3 coating applied on the steel? Please add this information to the article.
• How many samples were tested? What is the repeatability of the obtained results? The lack of this information in the text makes it difficult to assess the obtained research results.
• In the “4. Results and discussion” section, authors present their results but without any discussion supported by the literature. When the results are not discussed and conveniently supported by the open literature, questionable conclusions are obtained. Significant improvement in the description of the test results is required.
• In the last sentences in the section "4. Results and discussion", Authors wrote that nonlinear coefficients β’ can be used in evaluating the coat-ing bonding condition. There is one parameter that is useful for evaluation of adhesion between coating and substrate - it is reflection coefficient |r|. Also this parameter can be used for evaluation of the constitution and degradation process of the coating. What are the main differences between this two parameters? What are the advantages and disadvantages of these parameters and the scope of application in the assessment of adhesion of coatings to the substrate?
• Research articles should present the directions of further research. I suggest adding one paragraph in the conclusion.
• Please read the instructions on how to describe the references at the end of the article in the authors' guide and change it. Currently, the references at the end of the text are not in line with the journal requirements. For example, journal title and volume should be written by italic font. 

Specific, mainly editorial remarks and typos:

• line 31 - is "materials[1].", should be: materials [1],
• line 35 - is "Lescribaa et al.[2]", should be: Lescribaa et al. [2], the same remark (space missing) is for line 38 and 41,
• line 59 - is "degradations[18,19].", should be: degradations [18,19].,
• line 75 - is "by[20]", should be: by [20],
• line 125 - is "coefficient is defined as[22]", the space is missing also the number 22 is incorrect ?
• line 142 - the Figure 1 caption should be centered.
• line 160 - space is missing in Figure 4 caption: "...signal.(a) Time...",
• line 182 - is "in fig.5.", should be: in Fig. 5.,
• line 192 - is "fig-ure.6.", should be: Fig. 6,
• the authors wrote: "When the stretching stress is loaded to 260 MPa, the margins of the coating interface first produce the trans-versal cracks pointed by the red circles in Fig. 6 (b).". I can't find the red circle in Fig. 6b,
• line 211 - is "Fig. 7 show", should be Fig. 7 shows.

The article requires the above major changes. I hope, these suggestions can help to improve the quality of this paper.

I wish You all the best.

Author Response

Dear Reviewer,
Thank you for your affirmation of our research work. We have carefully considered and adopted the major changes you proposed in the text and revised the paper, which greatly improved the quality of the submitted manuscript. Thank you again for your help in reviewing the manuscript. Please see the attachment

Author Response File: Author Response.pdf

Reviewer 3 Report

Evaluation of damage process of a coating by using nonlinear ultrasonic method – Xu et al.

General comments: The article describes establishment of nonlinear parameters calibrated against tensile tests to be used as early stage parameters to detect damage in coating. The results are well presented and is of interest to the community. Specific comments are provided below.

Specific comments:

• Rewrite abstract; especially final few sentences in order to match well with scope of the paper.
• Page line 23: either use increasingly or extensively
• Section 3.3 indicates discrepancy between specimens which can also be caused due to surface preparation techniques. Were there any attempts to study the effect of surface preparation on these nonlinear parameters?
• It will aid the discussion if the derived parameters are tabulated.
• Figure 7 lacks clarity, they can be enlarged to read the axes labels.
• Request to fit a curve on Figure 7, especially on the second and third order nonlinear coefficient against stress values. This will aid in understanding the outliers using a fitted regression line.
• Rewrite Line 223.
• Expand Conclusions to discuss about the obtained nonlinear coefficients during tests.

Author Response

Dear Reviewer,

Thank you for your comments. We have carefully considered and adopted the comments you proposed in the text and revised the paper, which greatly improved the quality of the submitted manuscript. Thank you again for your help in reviewing the manuscript. Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Dear authors,
Thank you for updating the manuscript with recommended changes.

Reviewer 2 Report

Dear Authors,

thank you for considering my comments and improving the article.

Best regards

Reviewer