Effectiveness of Nanotechnology Treatments in Composite Aircraft Applications

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Introduction

1. The background of “nanotechnology” in the Introduction section (page 1) is redundancy. On the other hand, the background of the research in the paper is not clear enough. For example, what kind of nanotechnological treatments were applied in the previous literature? How does nanotechnological treatment affect the mechanical properties of the material? What is the gap between the literature and this paper? The novelty of the work should be emphasized.

2. Over half of the literature is not up-to-date (over 5 years). The number of citations should be improved, and more relative research should be referred to.

Major body of the manuscript

3. On page 3, Figure 2 and Table 1. The dimension of the specimen is confusing and not clear. The total length of A+B*2+R*2 is not equal to L. In addition, where is the end of L? What is the distance between L and D?

4. On page 3, line 80. “The dimensions of each specimen can be deduced from Figure 2 and Table 2.” Should it be Table 1?

5. On page 4, there is no explanation for Figure 3. What do “Raw 2024-T3", "Primer”, and “Nanotech” stand for? What is the difference among these specimens? The experiment should be clearly explained. It is also suggested to name all the specimens within the same series, such as S1, S2, S3.

6. What nanotechnology was used to treat the specimens? Is it based on the standard procedure or an in-house study? The process should also be included in the paper.

7. For figures 5-7, does MF 000 always be the reference specimen? If so, what is the cycle of failure under load type 2 and 3?

8. On page 5-7, why under load type 1, the specimen treated with nanotechnologies (MCF007) has a very similar behavior to the specimen of the same category not subjected to corrosion process (MCS10), but under load type 2 and 3, the difference is significantly increased?

9. In Figure 9, the scale is not consistent (20, 50, 200 μm). Specimens should be compared under the same set-up parameters, at least at the same magnification.

10. On page 9, line 215-216, the authors state that “at the same magnification, the corroded specimen, MCF 008, has the same number of holes and imperfections as the uncorroded one, MCS 216". However, on Figure 11, it is obvious that the specimens are not under the same magnifications, and the scale is not the same. The number of holes would not be the same, and therefore, the relative explanations and discussion should be questioned in this case. The same situation occurs in Figure 12.

11. The whole discussion section lacks scientific rigour. The paper just indicated the phenomenon, but not the reason for it. Is there any reference that could support the findings? The discussion section should be rewritten.

12. There are “Author Contributions, Funding, Acknowledgments, Conflicts of Interest” sections that are incomplete. It looks like a template without any contents.

Comments on the Quality of English Language

Moderate editing of English language required

Author Response

Answer to Reviewers:

The authors would like to thank the reviewers for their constructive comments and suggestions which helped improve the quality of the manuscript. The article has been revised accordingly to the reviews, and details of the changes are reported next. We hope that in this revised form the paper will meet the reviewers’ expectations and address their concerns/questions.

In green, the answers to the reviewers and the changes made to the manuscript are reported.

 

REVIEWER 1:

 

Introduction

1. The background of “nanotechnology” in the Introduction section (page 1) is redundancy. On the other hand, the background of the research in the paper is not clear enough. For example, what kind of nanotechnological treatments were applied in the previous literature? How does nanotechnological treatment affect the mechanical properties of the material? What is the gap between the literature and this paper? The novelty of the work should be emphasized.

Thank you for your valuable feedback and insightful questions regarding the Introduction section of our paper.

The literature concerning the use of nanotechnologies to enhance the performance of aerospace materials is certainly lacking in experimental evidence and procedures that quantitatively define their real effectiveness.

In the revised version we will highlight the gap between the existing literature and our paper by emphasizing the unique contribution and novelty of our work that mainly concern:

• experimental data on the fatigue life of aluminum alloy metallic samples treated with nanotechnologies and subjected to corrosion, demonstrating their effectiveness in fatigue extension also compared with standard Primer treatments.
• Definition of a completely new procedure for the quantitative evaluation of the improvement in cleanability characteristics when nanotechnology treatment is applied to various surfaces made of composite/metallic materials.

A recent (2024) review paper highlighting various Nanotechnology treatments to enhance fiber polymer composite performances is also introduced:

Rashid, Adib and Haque, Mahima and Islam, S.M. and Labib, K.M., Nanotechnology-enhanced fiber-reinforced polymer composites: Recent advancements on processing techniques and applications, 2024 Vol . 10 Heliyon Journal, 10.1016/j.heliyon.2024.e24692

2. Over half of the literature is not up-to-date (over 5 years). The number of citations should be improved, and more relative research should be referred to.

An interesting recent (2024) review paper has been introduced in the introduction:

He Zhu, Jingfei Li, “Advancements in corrosion protection for aerospace aluminum alloys through surface treatment” International Journal of Electrochemical Science, Volume 19, Issue 2, 2024,100487, ISSN 1452-3981, https://doi.org/10.1016/j.ijoes.2024.100487.

This review explores advancements in corrosion protection techniques for aerospace aluminum alloys, highlighting the transition from conventional methods such as chromate conversion coatings and anodizing to more sustainable and efficient alternatives. Recent developments encompass a spectrum of innovations, including rare earth element-based coatings, organic-inorganic hybrids, advanced polymer solutions, and the integration of nanotechnology.

Major body of the manuscript

3. On page 3, Figure 2 and Table 1. The dimension of the specimen is confusing and not clear. The total length of A+B*2+R*2 is not equal to L. In addition, where is the end of L? What is the distance between L and D?

We added C dimension, which was present in the table1 but not in the figure2. R indicates the radius, but the arc is not 90°, so it doesn't become 2R.

4. On page 3, line 80. “The dimensions of each specimen can be deduced from Figure 2 and Table 2.” Should it be Table 1?

Yes it is correct – modified in the new version

5. On page 4, there is no explanation for Figure 3. What do “Raw 2024-T3", "Primer”, and “Nanotech” stand for? What is the difference among these specimens? The experiment should be clearly explained. It is also suggested to name all the specimens within the same series, such as S1, S2, S3.

In the legend of the figure, the meaning of “Raw 2024-T3”, "Primer", "Nanotech" is clarified. The nomenclature of the specimens has not been changed because that would mean altering all the technical reports of the tests. Let's hope that this is clear enough.

6. What nanotechnology was used to treat the specimens? Is it based on the standard procedure or an in-house study? The process should also be included in the paper.

The process used for the treatment of the specimens was the spray coating, a widely recognized industrial method which involves the application of suspensions of diverse nanoparticles to cover a range of materials with varying shapes. Nanoparticles contained within atomized droplets are applied onto surfaces, resulting in a nanostructured coating once the liquid solvent evaporates. Spray coating offers several advantages over alternative methods, such as minimal liquid wastage, precise control over film thickness and surface roughness, and the ability to use a wide array of fluids with different viscosities. Its simplicity makes spray coating easily adaptable to large computer-controlled production systems.

A sentence in the revised text has been added as well as two new references:

Del Secco, B.; Trabucco, S.; Ravegnani, F.; Koivisto, A.; Zanoni, I.; Blosi, M.; Ortelli, S.; Altin, M.; Bartolini, G.; Costa, A.; et al. Particles Emission from an Industrial Spray Coating Process Using Nano-Materials. Nanomaterials 2022, 12, 313. https://doi.org/10.3390/nano12030313.

Girotto, C.; Rand, B.; Steudel, S.; Genoe, J.; Heremans, P. Nanoparticle-based, spray-coated silver top contacts for efficient polymer solar cells. Organic Electronics 2009, 10, 735–740. https://doi.org/10.1016/j.orgel.2009.03.006.

7. For figures 5-7, does MF 000 always be the reference specimen? If so, what is the cycle of failure under load type 2 and 3?

MF000 is the reference for untreated and uncorroded test specimen. Only in the case of Load Type 1, a fatigue test was conducted, which showed comparable values to those of MIL-HDBK5 for the same material (MF000-MIL). For Load Types 2 and 3, the values from MIL-HDBK5 have been included as a reference and indicated as MF000-MIL. The graphs have been modified by introducing the MIL-HDBK5 reference for all the Load Types. Figures 5, 6, and 7 graphs have been modified accordingly.

8. On page 5-7, why under load type 1, the specimen treated with nanotechnologies (MCF007) has a very similar behavior to the specimen of the same category not subjected to corrosion process (MCS10), but under load type 2 and 3, the difference is significantly increased?

This effect has also been observed in other papers discussing post-corrosion fatigue, particularly SN curves are also altered in their slope due to corrosion effects.

 

In all specimens subjected to corrosive immersion, a greater effect of corrosion was observed at lower loads (Load type 2 and 3), confirming not only an increase in the stress concentration factor (kt) but also a change in the slope, as indicated also in the following paper added in the reference list.

Yang, H-H and Wang, Y-L and Wang, Xi-Shu and Pan, Pan and Jia, D-W; Synergistic effect of environmental media and stress on the fatigue fracture behaviour of aluminium alloys. Vol 39 Journal of Fatigue & Fracture of Engineering Materials & Structures, doi = 10.1111/ffe.12457

Citation has been added in the revised version.

9. In Figure 9, the scale is not consistent (20, 50, 200 μm). Specimens should be compared under the same set-up parameters, at least at the same magnification.

The magnification scale used to compare the three specimens with different protective coatings is consistent and set at 100 micrometers. The first three photographs in Figure 9 (those positioned at the top) serve as exemplars and depict the type of damage intended to be highlighted: incisions and holes, imperfections resulting from the manufacturing process of the metal sheet from which the specimens were derived, exacerbated aesthetically by the corrosive and fatigue processes. The subsequent three photographs, positioned at the bottom, have varying magnifications, as the aim was simply to clearly illustrate the phenomenon of slip bands caused by the fatigue process: these images do not serve a comparative purpose but rather emphasize the presence of the same aesthetic characteristic in all three analyzed specimens.

10. On page 9, line 215-216, the authors state that “at the same magnification, the corroded specimen, MCF 008, has the same number of holes and imperfections as the uncorroded one, MCS 216". However, on Figure 11, it is obvious that the specimens are not under the same magnifications, and the scale is not the same. The number of holes would not be the same, and therefore, the relative explanations and discussion should be questioned in this case. The same situation occurs in Figure 12.

The reviewer's comment refers to the operational characteristic "Mag" of the microscope, without considering that the scale of representation in the two images of Figure 11 is the same, indeed set at 100 micrometers for both. The observation regarding the number of imperfections found in the two specimens is purely indicative and constrained by the quality and quantity of the collected images. This did not pose a limitation because aesthetic considerations were not a central part of the research but rather an ancillary aspect.

11. The whole discussion section lacks scientific rigour. The paper just indicated the phenomenon, but not the reason for it. Is there any reference that could support the findings? The discussion section should be rewritten.

The authors are further investigating the mechanism underlying the improvement of fatigue resistance in metallic materials when treated with silicate-based nanoparticles. At present, we can state that the initial cracks were noted to originate from pitting damage at numerous locations, as highlighted also in (Fonte 25), where a detailed narrative of the entire damage evolution process in corrosion-nucleated fatigue is provided.

Fonte25: Walde, K. and Hillberry, B.M., Initiation and shape development of corrosion-nucleated fatigue cracking, International Journal of Fatigue, 2007, Vol 29 pp1269-1281. 10.1016/j.ijfatigue.2006.10.010

A similar conclusion was derived in (Fonte26) where all the pre-corroded Al 2024-T4 specimens under investigation fractured from cracks associated with pitting. Results indicated that quantities such as pit surface area and surrounding pit proximity are as important as pit depth in determining when and where a crack will form. Same material of present work (Al2024-T3) was analyzed in (Fonte 27) and also in this case pit-to-crack transition was successfully observed using digital video techniques.

Fonte 26: Song, Haipeng and Liu, Changchun and Zhang, Hao and Leen, Sean “A DIC-Based Study on Fatigue Damage Evolution in Pre-Corroded Aluminum Alloy 2024-T4”; Materials 2018, Vol.11; 10.3390/ma11112243

Fonte 27: Jones, Kimberli and Hoeppner, David, “Prior corrosion and fatigue of 2024-T3 aluminum alloy” Corrosion Science - CORROS SCI Vol.48 2006 pp 3109-3122. 10.1016/j.corsci.2005.11.008

Since a reduction in the number and size of corrosion pits has been observed in specimens treated with nanotechnologies, this could correlate with the extension of fatigue life detected by experimental tests.

12. There are “Author Contributions, Funding, Acknowledgments, Conflicts of Interest” sections that are incomplete. It looks like a template without any contents.

Modified in the revised version.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Comments for author File: Comments.pdf

Comments on the Quality of English Language

The manuscript requires restructuring for clarity, particularly the absence of a dedicated results and discussion section.

Authors are encouraged to elaborate on the mechanisms through which silicate-based nanoparticles influence corrosion and fatigue behavior.

These suggestions aim to enhance the coherence and depth of the manuscript.

Author Response

Answer to Reviewers:

 The authors would like to thank the reviewers for their constructive comments and suggestions which helped improve the quality of the manuscript. The article has been revised accordingly to the reviews, and details of the changes are reported next. We hope that in this revised form the paper will meet the reviewers’ expectations and address their concerns/questions.

In green, the answers to the reviewers and the changes made to the manuscript are reported.

REVIEWER 2:

 The manuscript requires restructuring for clarity, particularly the absence of a dedicated results and discussion section.

Authors are encouraged to elaborate on the mechanisms through which silicate-based nanoparticles influence corrosion and fatigue behavior.

These suggestions aim to enhance the coherence and depth of the manuscript.

Thank you for your valuable feedback that was helpful to improve the quality of the paper. We hope that the revised version will meet the reviewer expectations.

1- The paper's format should be modified to adhere to a scientific paper format rather than resembling a report.

Authors followed MDPI instructions for scientific articles.

2- Line 106: Two measurements of the ph of the. It appears there may have been a typographical error.

ph modified in pH in the new version

3- Table 2: The term "load type" typically refers to the specific kind or category of load being applied or measured in a given context. In a table, it could specify whether the load being referenced is, for example, a mechanical load, an electrical load, a thermal load, etc. Clarifying the meaning of "load type" in the table would provide context for interpreting the data associated with each load entry.

Type indicates the type of fatigue cycle considered, as clarified in Table 2.

4- Fig 9: SEM images require adjustments to brightness and contrast, particularly in regions A and B, which appear excessively dark.

Figure 9 is not a SEM image. The SEM images provided are the best compromise between image clarity and legibility of the written text.

5- Fig 3, 13 and 14 The labels should be properly applied for clarity and accuracy.

Figure 3 has been modified introducing label description.

In figure 13 link to Table 4 has been added for labels definition

Figure 14 labels are linked to text description in the revised version.

6- Line 311

Comment is not clear to the authors.

7- In the conclusion, please specify the name of the treatment rather than simply referring to the last type of load, such as "primer treatment" and so on.

Comment is not clear to the authors.

8- Line: 324, Aluminum alloy: typo mistake

Modified in aluminium.

9- The manuscript needs proper structuring, lacking both a results and discussion section. Additionally, authors should provide detailed explanations on the impact of silicate-based nanoparticles on corrosion and fatigue behavior.

The authors are further investigating the mechanism underlying the improvement of fatigue resistance in metallic materials when treated with silicate-based nanoparticles. At present, we can state that the initial cracks were noted to originate from pitting damage at numerous locations, as highlighted also in (Fonte 25), where a detailed narrative of the entire damage evolution process in corrosion-nucleated fatigue is provided.

Fonte25: Walde, K. and Hillberry, B.M., Initiation and shape development of corrosion-nucleated fatigue cracking, International Journal of Fatigue, 2007, Vol 29 pp1269-1281. 10.1016/j.ijfatigue.2006.10.010

A similar conclusion was derived in (Fonte26) where all the pre-corroded Al 2024-T4 specimens under investigation fractured from cracks associated with pitting. Results indicated that quantities such as pit surface area and surrounding pit proximity are as important as pit depth in determining when and where a crack will form. Same material of present work (Al2024-T3) was analyzed in (Fonte 27) and also in this case pit-to-crack transition was successfully observed using digital video techniques.

Fonte 26: Song, Haipeng and Liu, Changchun and Zhang, Hao and Leen, Sean “A DIC-Based Study on Fatigue Damage Evolution in Pre-Corroded Aluminum Alloy 2024-T4”; Materials 2018, Vol.11; 10.3390/ma11112243

Fonte 27: Jones, Kimberli and Hoeppner, David, “Prior corrosion and fatigue of 2024-T3 aluminum alloy” Corrosion Science - CORROS SCI Vol.48 2006 pp 3109-3122. 10.1016/j.corsci.2005.11.008

Since a reduction in the number and size of corrosion pits has been observed in specimens treated with nanotechnologies, this could correlate with the extension of fatigue life detected by experimental tests.

 

 

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

1.       The reference in the paper is showing as [??]. There is no bibliography for the references at the end of the paper. Please fix in the content and the bibliography.

 

2.       There are some confusing issues for figure numbers (such as page 12, “Figure ??-A”). Please carefully review the manuscript and fix it.

Comments on the Quality of English Language

minor revision

Author Response

In the new version I have tried to recompile the tex file to fix the problems

Reviewer 2 Report

Comments and Suggestions for Authors

can be published in the current format

Author Response

Thanks for appreciating the changes made